102 files changed, 2540 insertions, 729 deletions

diff --git a/crates/assists/Cargo.toml b/crates/assists/Cargo.toml
index 264125651..108f656e9 100644
--- a/crates/assists/Cargo.toml
+++ b/crates/assists/Cargo.toml
@@ -18,7 +18,6 @@ stdx = { path = "../stdx", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
 text_edit = { path = "../text_edit", version = "0.0.0" }
 profile = { path = "../profile", version = "0.0.0" }
-base_db = { path = "../base_db", version = "0.0.0" }
 ide_db = { path = "../ide_db", version = "0.0.0" }
 hir = { path = "../hir", version = "0.0.0" }
 test_utils = { path = "../test_utils", version = "0.0.0" }
diff --git a/crates/assists/src/assist_context.rs b/crates/assists/src/assist_context.rs
index bf520069e..d11fee196 100644
--- a/crates/assists/src/assist_context.rs
+++ b/crates/assists/src/assist_context.rs
@@ -3,8 +3,8 @@
 use std::mem;
 
 use algo::find_covering_element;
-use base_db::{FileId, FileRange};
 use hir::Semantics;
+use ide_db::base_db::{FileId, FileRange};
 use ide_db::{
     label::Label,
     source_change::{SourceChange, SourceFileEdit},
diff --git a/crates/assists/src/handlers/add_missing_impl_members.rs b/crates/assists/src/handlers/add_missing_impl_members.rs
index 4c400f287..b82fb30ad 100644
--- a/crates/assists/src/handlers/add_missing_impl_members.rs
+++ b/crates/assists/src/handlers/add_missing_impl_members.rs
@@ -1,4 +1,5 @@
 use hir::HasSource;
+use ide_db::traits::{get_missing_assoc_items, resolve_target_trait};
 use syntax::{
     ast::{
         self,
@@ -11,7 +12,7 @@ use syntax::{
 use crate::{
     assist_context::{AssistContext, Assists},
     ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
-    utils::{get_missing_assoc_items, render_snippet, resolve_target_trait, Cursor},
+    utils::{render_snippet, Cursor},
     AssistId, AssistKind,
 };
 
diff --git a/crates/assists/src/handlers/extract_struct_from_enum_variant.rs b/crates/assists/src/handlers/extract_struct_from_enum_variant.rs
index 7f4f80b23..48433feb9 100644
--- a/crates/assists/src/handlers/extract_struct_from_enum_variant.rs
+++ b/crates/assists/src/handlers/extract_struct_from_enum_variant.rs
@@ -1,5 +1,5 @@
-use base_db::FileId;
 use hir::{EnumVariant, Module, ModuleDef, Name};
+use ide_db::base_db::FileId;
 use ide_db::{defs::Definition, search::Reference, RootDatabase};
 use itertools::Itertools;
 use rustc_hash::FxHashSet;
diff --git a/crates/assists/src/handlers/fix_visibility.rs b/crates/assists/src/handlers/fix_visibility.rs
index 66f74150c..c86720787 100644
--- a/crates/assists/src/handlers/fix_visibility.rs
+++ b/crates/assists/src/handlers/fix_visibility.rs
@@ -1,5 +1,5 @@
-use base_db::FileId;
 use hir::{db::HirDatabase, HasSource, HasVisibility, PathResolution};
+use ide_db::base_db::FileId;
 use syntax::{
     ast::{self, VisibilityOwner},
     AstNode, TextRange, TextSize,
diff --git a/crates/assists/src/handlers/generate_function.rs b/crates/assists/src/handlers/generate_function.rs
index d23f4293b..758188a42 100644
--- a/crates/assists/src/handlers/generate_function.rs
+++ b/crates/assists/src/handlers/generate_function.rs
@@ -1,5 +1,5 @@
-use base_db::FileId;
 use hir::HirDisplay;
+use ide_db::base_db::FileId;
 use rustc_hash::{FxHashMap, FxHashSet};
 use syntax::{
     ast::{
diff --git a/crates/assists/src/handlers/remove_dbg.rs b/crates/assists/src/handlers/remove_dbg.rs
index e10616779..9731344b8 100644
--- a/crates/assists/src/handlers/remove_dbg.rs
+++ b/crates/assists/src/handlers/remove_dbg.rs
@@ -93,8 +93,9 @@ fn needs_parentheses_around_macro_contents(macro_contents: Vec<SyntaxElement>) -
     if macro_contents.len() < 2 {
         return false;
     }
+    let mut macro_contents = macro_contents.into_iter().peekable();
     let mut unpaired_brackets_in_contents = Vec::new();
-    for element in macro_contents {
+    while let Some(element) = macro_contents.next() {
         match element.kind() {
             T!['('] | T!['['] | T!['{'] => unpaired_brackets_in_contents.push(element),
             T![')'] => {
@@ -118,8 +119,14 @@ fn needs_parentheses_around_macro_contents(macro_contents: Vec<SyntaxElement>) -
             symbol_kind => {
                 let symbol_not_in_bracket = unpaired_brackets_in_contents.is_empty();
                 if symbol_not_in_bracket
-                    && symbol_kind != SyntaxKind::COLON
-                    && symbol_kind.is_punct()
+                    && symbol_kind != SyntaxKind::COLON // paths
+                    && (symbol_kind != SyntaxKind::DOT // field/method access
+                        || macro_contents // range expressions consist of two SyntaxKind::Dot in macro invocations
+                            .peek()
+                            .map(|element| element.kind() == SyntaxKind::DOT)
+                            .unwrap_or(false))
+                    && symbol_kind != SyntaxKind::QUESTION // try operator
+                    && (symbol_kind.is_punct() || symbol_kind == SyntaxKind::AS_KW)
                 {
                     return true;
                 }
@@ -243,6 +250,25 @@ fn main() {
     }
 
     #[test]
+    fn test_remove_dbg_method_chaining() {
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(foo().bar()).baz();"#,
+            r#"let res = foo().bar().baz();"#,
+        );
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(foo.bar()).baz();"#,
+            r#"let res = foo.bar().baz();"#,
+        );
+    }
+
+    #[test]
+    fn test_remove_dbg_field_chaining() {
+        check_assist(remove_dbg, r#"let res = <|>dbg!(foo.bar).baz;"#, r#"let res = foo.bar.baz;"#);
+    }
+
+    #[test]
     fn test_remove_dbg_from_inside_fn() {
         check_assist_target(
             remove_dbg,
@@ -280,4 +306,59 @@ fn main() {
 }"#,
         );
     }
+
+    #[test]
+    fn test_remove_dbg_try_expr() {
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(result?).foo();"#,
+            r#"let res = result?.foo();"#,
+        );
+    }
+
+    #[test]
+    fn test_remove_dbg_await_expr() {
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(fut.await).foo();"#,
+            r#"let res = fut.await.foo();"#,
+        );
+    }
+
+    #[test]
+    fn test_remove_dbg_as_cast() {
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(3 as usize).foo();"#,
+            r#"let res = (3 as usize).foo();"#,
+        );
+    }
+
+    #[test]
+    fn test_remove_dbg_index_expr() {
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(array[3]).foo();"#,
+            r#"let res = array[3].foo();"#,
+        );
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(tuple.3).foo();"#,
+            r#"let res = tuple.3.foo();"#,
+        );
+    }
+
+    #[test]
+    fn test_remove_dbg_range_expr() {
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(foo..bar).foo();"#,
+            r#"let res = (foo..bar).foo();"#,
+        );
+        check_assist(
+            remove_dbg,
+            r#"let res = <|>dbg!(foo..=bar).foo();"#,
+            r#"let res = (foo..=bar).foo();"#,
+        );
+    }
 }
diff --git a/crates/assists/src/handlers/replace_if_let_with_match.rs b/crates/assists/src/handlers/replace_if_let_with_match.rs
index 79097621e..9a49c48c1 100644
--- a/crates/assists/src/handlers/replace_if_let_with_match.rs
+++ b/crates/assists/src/handlers/replace_if_let_with_match.rs
@@ -7,10 +7,8 @@ use syntax::{
     AstNode,
 };
 
-use crate::{
-    utils::{unwrap_trivial_block, TryEnum},
-    AssistContext, AssistId, AssistKind, Assists,
-};
+use crate::{utils::unwrap_trivial_block, AssistContext, AssistId, AssistKind, Assists};
+use ide_db::ty_filter::TryEnum;
 
 // Assist: replace_if_let_with_match
 //
diff --git a/crates/assists/src/handlers/replace_let_with_if_let.rs b/crates/assists/src/handlers/replace_let_with_if_let.rs
index ed6d0c29b..a5bcbda24 100644
--- a/crates/assists/src/handlers/replace_let_with_if_let.rs
+++ b/crates/assists/src/handlers/replace_let_with_if_let.rs
@@ -9,7 +9,8 @@ use syntax::{
     AstNode, T,
 };
 
-use crate::{utils::TryEnum, AssistContext, AssistId, AssistKind, Assists};
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+use ide_db::ty_filter::TryEnum;
 
 // Assist: replace_let_with_if_let
 //
diff --git a/crates/assists/src/handlers/replace_unwrap_with_match.rs b/crates/assists/src/handlers/replace_unwrap_with_match.rs
index 4043c219c..f547066f0 100644
--- a/crates/assists/src/handlers/replace_unwrap_with_match.rs
+++ b/crates/assists/src/handlers/replace_unwrap_with_match.rs
@@ -10,9 +10,10 @@ use syntax::{
 };
 
 use crate::{
-    utils::{render_snippet, Cursor, TryEnum},
+    utils::{render_snippet, Cursor},
     AssistContext, AssistId, AssistKind, Assists,
 };
+use ide_db::ty_filter::TryEnum;
 
 // Assist: replace_unwrap_with_match
 //
diff --git a/crates/assists/src/lib.rs b/crates/assists/src/lib.rs
index 8a664f654..70a651e10 100644
--- a/crates/assists/src/lib.rs
+++ b/crates/assists/src/lib.rs
@@ -17,8 +17,8 @@ mod tests;
 pub mod utils;
 pub mod ast_transform;
 
-use base_db::FileRange;
 use hir::Semantics;
+use ide_db::base_db::FileRange;
 use ide_db::{label::Label, source_change::SourceChange, RootDatabase};
 use syntax::TextRange;
 
diff --git a/crates/assists/src/tests.rs b/crates/assists/src/tests.rs
index 2b687decf..849d85e76 100644
--- a/crates/assists/src/tests.rs
+++ b/crates/assists/src/tests.rs
@@ -1,7 +1,7 @@
 mod generated;
 
-use base_db::{fixture::WithFixture, FileId, FileRange, SourceDatabaseExt};
 use hir::Semantics;
+use ide_db::base_db::{fixture::WithFixture, FileId, FileRange, SourceDatabaseExt};
 use ide_db::RootDatabase;
 use syntax::TextRange;
 use test_utils::{assert_eq_text, extract_offset, extract_range};
diff --git a/crates/assists/src/utils.rs b/crates/assists/src/utils.rs
index 1a6b48b45..56f925ee6 100644
--- a/crates/assists/src/utils.rs
+++ b/crates/assists/src/utils.rs
@@ -2,14 +2,13 @@
 pub(crate) mod insert_use;
 pub(crate) mod import_assets;
 
-use std::{iter, ops};
+use std::ops;
 
-use hir::{Adt, Crate, Enum, Module, ScopeDef, Semantics, Trait, Type};
+use hir::{Crate, Enum, Module, ScopeDef, Semantics, Trait};
 use ide_db::RootDatabase;
 use itertools::Itertools;
-use rustc_hash::FxHashSet;
 use syntax::{
-    ast::{self, make, ArgListOwner, NameOwner},
+    ast::{self, make, ArgListOwner},
     AstNode, Direction,
     SyntaxKind::*,
     SyntaxNode, TextSize, T,
@@ -115,72 +114,6 @@ pub(crate) fn render_snippet(_cap: SnippetCap, node: &SyntaxNode, cursor: Cursor
     }
 }
 
-pub fn get_missing_assoc_items(
-    sema: &Semantics<RootDatabase>,
-    impl_def: &ast::Impl,
-) -> Vec<hir::AssocItem> {
-    // Names must be unique between constants and functions. However, type aliases
-    // may share the same name as a function or constant.
-    let mut impl_fns_consts = FxHashSet::default();
-    let mut impl_type = FxHashSet::default();
-
-    if let Some(item_list) = impl_def.assoc_item_list() {
-        for item in item_list.assoc_items() {
-            match item {
-                ast::AssocItem::Fn(f) => {
-                    if let Some(n) = f.name() {
-                        impl_fns_consts.insert(n.syntax().to_string());
-                    }
-                }
-
-                ast::AssocItem::TypeAlias(t) => {
-                    if let Some(n) = t.name() {
-                        impl_type.insert(n.syntax().to_string());
-                    }
-                }
-
-                ast::AssocItem::Const(c) => {
-                    if let Some(n) = c.name() {
-                        impl_fns_consts.insert(n.syntax().to_string());
-                    }
-                }
-                ast::AssocItem::MacroCall(_) => (),
-            }
-        }
-    }
-
-    resolve_target_trait(sema, impl_def).map_or(vec![], |target_trait| {
-        target_trait
-            .items(sema.db)
-            .iter()
-            .filter(|i| match i {
-                hir::AssocItem::Function(f) => {
-                    !impl_fns_consts.contains(&f.name(sema.db).to_string())
-                }
-                hir::AssocItem::TypeAlias(t) => !impl_type.contains(&t.name(sema.db).to_string()),
-                hir::AssocItem::Const(c) => c
-                    .name(sema.db)
-                    .map(|n| !impl_fns_consts.contains(&n.to_string()))
-                    .unwrap_or_default(),
-            })
-            .cloned()
-            .collect()
-    })
-}
-
-pub(crate) fn resolve_target_trait(
-    sema: &Semantics<RootDatabase>,
-    impl_def: &ast::Impl,
-) -> Option<hir::Trait> {
-    let ast_path =
-        impl_def.trait_().map(|it| it.syntax().clone()).and_then(ast::PathType::cast)?.path()?;
-
-    match sema.resolve_path(&ast_path) {
-        Some(hir::PathResolution::Def(hir::ModuleDef::Trait(def))) => Some(def),
-        _ => None,
-    }
-}
-
 pub(crate) fn vis_offset(node: &SyntaxNode) -> TextSize {
     node.children_with_tokens()
         .find(|it| !matches!(it.kind(), WHITESPACE | COMMENT | ATTR))
@@ -223,54 +156,6 @@ fn invert_special_case(expr: &ast::Expr) -> Option<ast::Expr> {
     }
 }
 
-#[derive(Clone, Copy)]
-pub enum TryEnum {
-    Result,
-    Option,
-}
-
-impl TryEnum {
-    const ALL: [TryEnum; 2] = [TryEnum::Option, TryEnum::Result];
-
-    pub fn from_ty(sema: &Semantics<RootDatabase>, ty: &Type) -> Option<TryEnum> {
-        let enum_ = match ty.as_adt() {
-            Some(Adt::Enum(it)) => it,
-            _ => return None,
-        };
-        TryEnum::ALL.iter().find_map(|&var| {
-            if &enum_.name(sema.db).to_string() == var.type_name() {
-                return Some(var);
-            }
-            None
-        })
-    }
-
-    pub(crate) fn happy_case(self) -> &'static str {
-        match self {
-            TryEnum::Result => "Ok",
-            TryEnum::Option => "Some",
-        }
-    }
-
-    pub(crate) fn sad_pattern(self) -> ast::Pat {
-        match self {
-            TryEnum::Result => make::tuple_struct_pat(
-                make::path_unqualified(make::path_segment(make::name_ref("Err"))),
-                iter::once(make::wildcard_pat().into()),
-            )
-            .into(),
-            TryEnum::Option => make::ident_pat(make::name("None")).into(),
-        }
-    }
-
-    fn type_name(self) -> &'static str {
-        match self {
-            TryEnum::Result => "Result",
-            TryEnum::Option => "Option",
-        }
-    }
-}
-
 /// Helps with finding well-know things inside the standard library. This is
 /// somewhat similar to the known paths infra inside hir, but it different; We
 /// want to make sure that IDE specific paths don't become interesting inside
diff --git a/crates/assists/src/utils/insert_use.rs b/crates/assists/src/utils/insert_use.rs
index 409985b3b..033fbcedc 100644
--- a/crates/assists/src/utils/insert_use.rs
+++ b/crates/assists/src/utils/insert_use.rs
@@ -14,6 +14,7 @@ use syntax::{
     },
     InsertPosition, SyntaxElement, SyntaxNode,
 };
+use test_utils::mark;
 
 #[derive(Debug)]
 pub enum ImportScope {
@@ -109,6 +110,12 @@ pub(crate) fn insert_use(
     // so look for the place we have to insert to
     let (insert_position, add_blank) = find_insert_position(scope, path);
 
+    let indent = if let ident_level @ 1..=usize::MAX = scope.indent_level().0 as usize {
+        Some(make::tokens::whitespace(&" ".repeat(4 * ident_level)).into())
+    } else {
+        None
+    };
+
     let to_insert: Vec<SyntaxElement> = {
         let mut buf = Vec::new();
 
@@ -120,9 +127,13 @@ pub(crate) fn insert_use(
             _ => (),
         }
 
-        if let ident_level @ 1..=usize::MAX = scope.indent_level().0 as usize {
-            buf.push(make::tokens::whitespace(&" ".repeat(4 * ident_level)).into());
+        if add_blank.has_before() {
+            if let Some(indent) = indent.clone() {
+                mark::hit!(insert_use_indent_before);
+                buf.push(indent);
+            }
         }
+
         buf.push(use_item.syntax().clone().into());
 
         match add_blank {
@@ -133,6 +144,16 @@ pub(crate) fn insert_use(
             _ => (),
         }
 
+        // only add indentation *after* our stuff if there's another node directly after it
+        if add_blank.has_after() && matches!(insert_position, InsertPosition::Before(_)) {
+            if let Some(indent) = indent {
+                mark::hit!(insert_use_indent_after);
+                buf.push(indent);
+            }
+        } else if add_blank.has_after() && matches!(insert_position, InsertPosition::After(_)) {
+            mark::hit!(insert_use_no_indent_after);
+        }
+
         buf
     };
 
@@ -470,6 +491,15 @@ enum AddBlankLine {
     AfterTwice,
 }
 
+impl AddBlankLine {
+    fn has_before(&self) -> bool {
+        matches!(self, AddBlankLine::Before | AddBlankLine::BeforeTwice | AddBlankLine::Around)
+    }
+    fn has_after(&self) -> bool {
+        matches!(self, AddBlankLine::After | AddBlankLine::AfterTwice | AddBlankLine::Around)
+    }
+}
+
 fn find_insert_position(
     scope: &ImportScope,
     insert_path: ast::Path,
@@ -562,6 +592,21 @@ use std::bar::G;",
     }
 
     #[test]
+    fn insert_start_indent() {
+        mark::check!(insert_use_indent_after);
+        check_none(
+            "std::bar::AA",
+            r"
+    use std::bar::B;
+    use std::bar::D;",
+            r"
+    use std::bar::AA;
+    use std::bar::B;
+    use std::bar::D;",
+        )
+    }
+
+    #[test]
     fn insert_middle() {
         check_none(
             "std::bar::EE",
@@ -580,6 +625,24 @@ use std::bar::G;",
     }
 
     #[test]
+    fn insert_middle_indent() {
+        check_none(
+            "std::bar::EE",
+            r"
+    use std::bar::A;
+    use std::bar::D;
+    use std::bar::F;
+    use std::bar::G;",
+            r"
+    use std::bar::A;
+    use std::bar::D;
+    use std::bar::EE;
+    use std::bar::F;
+    use std::bar::G;",
+        )
+    }
+
+    #[test]
     fn insert_end() {
         check_none(
             "std::bar::ZZ",
@@ -598,6 +661,25 @@ use std::bar::ZZ;",
     }
 
     #[test]
+    fn insert_end_indent() {
+        mark::check!(insert_use_indent_before);
+        check_none(
+            "std::bar::ZZ",
+            r"
+    use std::bar::A;
+    use std::bar::D;
+    use std::bar::F;
+    use std::bar::G;",
+            r"
+    use std::bar::A;
+    use std::bar::D;
+    use std::bar::F;
+    use std::bar::G;
+    use std::bar::ZZ;",
+        )
+    }
+
+    #[test]
     fn insert_middle_nested() {
         check_none(
             "std::bar::EE",
@@ -620,18 +702,18 @@ use std::bar::G;",
         check_none(
             "foo::bar::GG",
             r"
-use std::bar::A;
-use std::bar::D;
+    use std::bar::A;
+    use std::bar::D;
 
-use foo::bar::F;
-use foo::bar::H;",
+    use foo::bar::F;
+    use foo::bar::H;",
             r"
-use std::bar::A;
-use std::bar::D;
+    use std::bar::A;
+    use std::bar::D;
 
-use foo::bar::F;
-use foo::bar::GG;
-use foo::bar::H;",
+    use foo::bar::F;
+    use foo::bar::GG;
+    use foo::bar::H;",
         )
     }
 
@@ -640,22 +722,22 @@ use foo::bar::H;",
         check_none(
             "foo::bar::GG",
             r"
-use foo::bar::A;
-use foo::bar::D;
+    use foo::bar::A;
+    use foo::bar::D;
 
-use std;
+    use std;
 
-use foo::bar::F;
-use foo::bar::H;",
+    use foo::bar::F;
+    use foo::bar::H;",
             r"
-use foo::bar::A;
-use foo::bar::D;
-use foo::bar::GG;
+    use foo::bar::A;
+    use foo::bar::D;
+    use foo::bar::GG;
 
-use std;
+    use std;
 
-use foo::bar::F;
-use foo::bar::H;",
+    use foo::bar::F;
+    use foo::bar::H;",
         )
     }
 
@@ -664,13 +746,13 @@ use foo::bar::H;",
         check_none(
             "std::fmt",
             r"
-use foo::bar::A;
-use foo::bar::D;",
+    use foo::bar::A;
+    use foo::bar::D;",
             r"
-use std::fmt;
+    use std::fmt;
 
-use foo::bar::A;
-use foo::bar::D;",
+    use foo::bar::A;
+    use foo::bar::D;",
         )
     }
 
@@ -714,6 +796,20 @@ fn main() {}",
     }
 
     #[test]
+    fn insert_empty_module() {
+        mark::check!(insert_use_no_indent_after);
+        check(
+            "foo::bar",
+            "mod x {}",
+            r"{
+    use foo::bar;
+}",
+            None,
+            true,
+        )
+    }
+
+    #[test]
     fn insert_after_inner_attr() {
         check_full(
             "foo::bar",
@@ -991,11 +1087,13 @@ use foo::bar::baz::Qux;",
         ra_fixture_before: &str,
         ra_fixture_after: &str,
         mb: Option<MergeBehaviour>,
+        module: bool,
     ) {
-        let file = super::ImportScope::from(
-            ast::SourceFile::parse(ra_fixture_before).tree().syntax().clone(),
-        )
-        .unwrap();
+        let mut syntax = ast::SourceFile::parse(ra_fixture_before).tree().syntax().clone();
+        if module {
+            syntax = syntax.descendants().find_map(ast::Module::cast).unwrap().syntax().clone();
+        }
+        let file = super::ImportScope::from(syntax).unwrap();
         let path = ast::SourceFile::parse(&format!("use {};", path))
             .tree()
             .syntax()
@@ -1008,15 +1106,15 @@ use foo::bar::baz::Qux;",
     }
 
     fn check_full(path: &str, ra_fixture_before: &str, ra_fixture_after: &str) {
-        check(path, ra_fixture_before, ra_fixture_after, Some(MergeBehaviour::Full))
+        check(path, ra_fixture_before, ra_fixture_after, Some(MergeBehaviour::Full), false)
     }
 
     fn check_last(path: &str, ra_fixture_before: &str, ra_fixture_after: &str) {
-        check(path, ra_fixture_before, ra_fixture_after, Some(MergeBehaviour::Last))
+        check(path, ra_fixture_before, ra_fixture_after, Some(MergeBehaviour::Last), false)
     }
 
     fn check_none(path: &str, ra_fixture_before: &str, ra_fixture_after: &str) {
-        check(path, ra_fixture_before, ra_fixture_after, None)
+        check(path, ra_fixture_before, ra_fixture_after, None, false)
     }
 
     fn check_merge_only_fail(ra_fixture0: &str, ra_fixture1: &str, mb: MergeBehaviour) {
diff --git a/crates/call_info/Cargo.toml b/crates/call_info/Cargo.toml
deleted file mode 100644
index 98c0bd6db..000000000
--- a/crates/call_info/Cargo.toml
+++ /dev/null
@@ -1,26 +0,0 @@
-[package]
-name = "call_info"
-version = "0.0.0"
-description = "TBD"
-license = "MIT OR Apache-2.0"
-authors = ["rust-analyzer developers"]
-edition = "2018"
-
-[lib]
-doctest = false
-
-[dependencies]
-either = "1.5.3"
-
-stdx = { path = "../stdx", version = "0.0.0" }
-syntax = { path = "../syntax", version = "0.0.0" }
-base_db = { path = "../base_db", version = "0.0.0" }
-ide_db = { path = "../ide_db", version = "0.0.0" }
-test_utils = { path = "../test_utils", version = "0.0.0" }
-
-# call_info crate should depend only on the top-level `hir` package. if you need
-# something from some `hir_xxx` subpackage, reexport the API via `hir`.
-hir = { path = "../hir", version = "0.0.0" }
-
-[dev-dependencies]
-expect-test = "1.0"
diff --git a/crates/cfg/Cargo.toml b/crates/cfg/Cargo.toml
index a6785ee8e..c68e391c1 100644
--- a/crates/cfg/Cargo.toml
+++ b/crates/cfg/Cargo.toml
@@ -17,3 +17,4 @@ tt = { path = "../tt", version = "0.0.0" }
 [dev-dependencies]
 mbe = { path = "../mbe" }
 syntax = { path = "../syntax" }
+expect-test = "1.0"
diff --git a/crates/cfg/src/cfg_expr.rs b/crates/cfg/src/cfg_expr.rs
index 336fe25bc..42327f1e1 100644
--- a/crates/cfg/src/cfg_expr.rs
+++ b/crates/cfg/src/cfg_expr.rs
@@ -2,30 +2,77 @@
 //!
 //! See: https://doc.rust-lang.org/reference/conditional-compilation.html#conditional-compilation
 
-use std::slice::Iter as SliceIter;
+use std::{fmt, slice::Iter as SliceIter};
 
 use tt::SmolStr;
 
+/// A simple configuration value passed in from the outside.
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Ord, PartialOrd)]
+pub enum CfgAtom {
+    /// eg. `#[cfg(test)]`
+    Flag(SmolStr),
+    /// eg. `#[cfg(target_os = "linux")]`
+    ///
+    /// Note that a key can have multiple values that are all considered "active" at the same time.
+    /// For example, `#[cfg(target_feature = "sse")]` and `#[cfg(target_feature = "sse2")]`.
+    KeyValue { key: SmolStr, value: SmolStr },
+}
+
+impl CfgAtom {
+    /// Returns `true` when the atom comes from the target specification.
+    ///
+    /// If this returns `true`, then changing this atom requires changing the compilation target. If
+    /// it returns `false`, the atom might come from a build script or the build system.
+    pub fn is_target_defined(&self) -> bool {
+        match self {
+            CfgAtom::Flag(flag) => matches!(&**flag, "unix" | "windows"),
+            CfgAtom::KeyValue { key, value: _ } => matches!(
+                &**key,
+                "target_arch"
+                    | "target_os"
+                    | "target_env"
+                    | "target_family"
+                    | "target_endian"
+                    | "target_pointer_width"
+                    | "target_vendor" // NOTE: `target_feature` is left out since it can be configured via `-Ctarget-feature`
+            ),
+        }
+    }
+}
+
+impl fmt::Display for CfgAtom {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            CfgAtom::Flag(name) => write!(f, "{}", name),
+            CfgAtom::KeyValue { key, value } => write!(f, "{} = {:?}", key, value),
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum CfgExpr {
     Invalid,
-    Atom(SmolStr),
-    KeyValue { key: SmolStr, value: SmolStr },
+    Atom(CfgAtom),
     All(Vec<CfgExpr>),
     Any(Vec<CfgExpr>),
     Not(Box<CfgExpr>),
 }
 
+impl From<CfgAtom> for CfgExpr {
+    fn from(atom: CfgAtom) -> Self {
+        CfgExpr::Atom(atom)
+    }
+}
+
 impl CfgExpr {
     pub fn parse(tt: &tt::Subtree) -> CfgExpr {
         next_cfg_expr(&mut tt.token_trees.iter()).unwrap_or(CfgExpr::Invalid)
     }
     /// Fold the cfg by querying all basic `Atom` and `KeyValue` predicates.
-    pub fn fold(&self, query: &dyn Fn(&SmolStr, Option<&SmolStr>) -> bool) -> Option<bool> {
+    pub fn fold(&self, query: &dyn Fn(&CfgAtom) -> bool) -> Option<bool> {
         match self {
             CfgExpr::Invalid => None,
-            CfgExpr::Atom(name) => Some(query(name, None)),
-            CfgExpr::KeyValue { key, value } => Some(query(key, Some(value))),
+            CfgExpr::Atom(atom) => Some(query(atom)),
             CfgExpr::All(preds) => {
                 preds.iter().try_fold(true, |s, pred| Some(s && pred.fold(query)?))
             }
@@ -54,7 +101,7 @@ fn next_cfg_expr(it: &mut SliceIter<tt::TokenTree>) -> Option<CfgExpr> {
                     // FIXME: escape? raw string?
                     let value =
                         SmolStr::new(literal.text.trim_start_matches('"').trim_end_matches('"'));
-                    CfgExpr::KeyValue { key: name, value }
+                    CfgAtom::KeyValue { key: name, value }.into()
                 }
                 _ => return Some(CfgExpr::Invalid),
             }
@@ -70,7 +117,7 @@ fn next_cfg_expr(it: &mut SliceIter<tt::TokenTree>) -> Option<CfgExpr> {
                 _ => CfgExpr::Invalid,
             }
         }
-        _ => CfgExpr::Atom(name),
+        _ => CfgAtom::Flag(name).into(),
     };
 
     // Eat comma separator
@@ -81,53 +128,3 @@ fn next_cfg_expr(it: &mut SliceIter<tt::TokenTree>) -> Option<CfgExpr> {
     }
     Some(ret)
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    use mbe::ast_to_token_tree;
-    use syntax::ast::{self, AstNode};
-
-    fn assert_parse_result(input: &str, expected: CfgExpr) {
-        let (tt, _) = {
-            let source_file = ast::SourceFile::parse(input).ok().unwrap();
-            let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
-            ast_to_token_tree(&tt).unwrap()
-        };
-        let cfg = CfgExpr::parse(&tt);
-        assert_eq!(cfg, expected);
-    }
-
-    #[test]
-    fn test_cfg_expr_parser() {
-        assert_parse_result("#![cfg(foo)]", CfgExpr::Atom("foo".into()));
-        assert_parse_result("#![cfg(foo,)]", CfgExpr::Atom("foo".into()));
-        assert_parse_result(
-            "#![cfg(not(foo))]",
-            CfgExpr::Not(Box::new(CfgExpr::Atom("foo".into()))),
-        );
-        assert_parse_result("#![cfg(foo(bar))]", CfgExpr::Invalid);
-
-        // Only take the first
-        assert_parse_result(r#"#![cfg(foo, bar = "baz")]"#, CfgExpr::Atom("foo".into()));
-
-        assert_parse_result(
-            r#"#![cfg(all(foo, bar = "baz"))]"#,
-            CfgExpr::All(vec![
-                CfgExpr::Atom("foo".into()),
-                CfgExpr::KeyValue { key: "bar".into(), value: "baz".into() },
-            ]),
-        );
-
-        assert_parse_result(
-            r#"#![cfg(any(not(), all(), , bar = "baz",))]"#,
-            CfgExpr::Any(vec![
-                CfgExpr::Not(Box::new(CfgExpr::Invalid)),
-                CfgExpr::All(vec![]),
-                CfgExpr::Invalid,
-                CfgExpr::KeyValue { key: "bar".into(), value: "baz".into() },
-            ]),
-        );
-    }
-}
diff --git a/crates/cfg/src/dnf.rs b/crates/cfg/src/dnf.rs
new file mode 100644
index 000000000..580c9a9a2
--- /dev/null
+++ b/crates/cfg/src/dnf.rs
@@ -0,0 +1,320 @@
+//! Disjunctive Normal Form construction.
+//!
+//! Algorithm from <https://www.cs.drexel.edu/~jjohnson/2015-16/fall/CS270/Lectures/3/dnf.pdf>,
+//! which would have been much easier to read if it used pattern matching. It's also missing the
+//! entire "distribute ANDs over ORs" part, which is not trivial. Oh well.
+//!
+//! This is currently both messy and inefficient. Feel free to improve, there are unit tests.
+
+use std::fmt;
+
+use rustc_hash::FxHashSet;
+
+use crate::{CfgAtom, CfgDiff, CfgExpr, CfgOptions, InactiveReason};
+
+/// A `#[cfg]` directive in Disjunctive Normal Form (DNF).
+pub struct DnfExpr {
+    conjunctions: Vec<Conjunction>,
+}
+
+struct Conjunction {
+    literals: Vec<Literal>,
+}
+
+struct Literal {
+    negate: bool,
+    var: Option<CfgAtom>, // None = Invalid
+}
+
+impl DnfExpr {
+    pub fn new(expr: CfgExpr) -> Self {
+        let builder = Builder { expr: DnfExpr { conjunctions: Vec::new() } };
+
+        builder.lower(expr.clone())
+    }
+
+    /// Computes a list of present or absent atoms in `opts` that cause this expression to evaluate
+    /// to `false`.
+    ///
+    /// Note that flipping a subset of these atoms might be sufficient to make the whole expression
+    /// evaluate to `true`. For that, see `compute_enable_hints`.
+    ///
+    /// Returns `None` when `self` is already true, or contains errors.
+    pub fn why_inactive(&self, opts: &CfgOptions) -> Option<InactiveReason> {
+        let mut res = InactiveReason { enabled: Vec::new(), disabled: Vec::new() };
+
+        for conj in &self.conjunctions {
+            let mut conj_is_true = true;
+            for lit in &conj.literals {
+                let atom = lit.var.as_ref()?;
+                let enabled = opts.enabled.contains(atom);
+                if lit.negate == enabled {
+                    // Literal is false, but needs to be true for this conjunction.
+                    conj_is_true = false;
+
+                    if enabled {
+                        res.enabled.push(atom.clone());
+                    } else {
+                        res.disabled.push(atom.clone());
+                    }
+                }
+            }
+
+            if conj_is_true {
+                // This expression is not actually inactive.
+                return None;
+            }
+        }
+
+        res.enabled.sort_unstable();
+        res.enabled.dedup();
+        res.disabled.sort_unstable();
+        res.disabled.dedup();
+        Some(res)
+    }
+
+    /// Returns `CfgDiff` objects that would enable this directive if applied to `opts`.
+    pub fn compute_enable_hints<'a>(
+        &'a self,
+        opts: &'a CfgOptions,
+    ) -> impl Iterator<Item = CfgDiff> + 'a {
+        // A cfg is enabled if any of `self.conjunctions` evaluate to `true`.
+
+        self.conjunctions.iter().filter_map(move |conj| {
+            let mut enable = FxHashSet::default();
+            let mut disable = FxHashSet::default();
+            for lit in &conj.literals {
+                let atom = lit.var.as_ref()?;
+                let enabled = opts.enabled.contains(atom);
+                if lit.negate && enabled {
+                    disable.insert(atom.clone());
+                }
+                if !lit.negate && !enabled {
+                    enable.insert(atom.clone());
+                }
+            }
+
+            // Check that this actually makes `conj` true.
+            for lit in &conj.literals {
+                let atom = lit.var.as_ref()?;
+                let enabled = enable.contains(atom)
+                    || (opts.enabled.contains(atom) && !disable.contains(atom));
+                if enabled == lit.negate {
+                    return None;
+                }
+            }
+
+            if enable.is_empty() && disable.is_empty() {
+                return None;
+            }
+
+            let mut diff = CfgDiff {
+                enable: enable.into_iter().collect(),
+                disable: disable.into_iter().collect(),
+            };
+
+            // Undo the FxHashMap randomization for consistent output.
+            diff.enable.sort_unstable();
+            diff.disable.sort_unstable();
+
+            Some(diff)
+        })
+    }
+}
+
+impl fmt::Display for DnfExpr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.conjunctions.len() != 1 {
+            write!(f, "any(")?;
+        }
+        for (i, conj) in self.conjunctions.iter().enumerate() {
+            if i != 0 {
+                f.write_str(", ")?;
+            }
+
+            write!(f, "{}", conj)?;
+        }
+        if self.conjunctions.len() != 1 {
+            write!(f, ")")?;
+        }
+
+        Ok(())
+    }
+}
+
+impl Conjunction {
+    fn new(parts: Vec<CfgExpr>) -> Self {
+        let mut literals = Vec::new();
+        for part in parts {
+            match part {
+                CfgExpr::Invalid | CfgExpr::Atom(_) | CfgExpr::Not(_) => {
+                    literals.push(Literal::new(part));
+                }
+                CfgExpr::All(conj) => {
+                    // Flatten.
+                    literals.extend(Conjunction::new(conj).literals);
+                }
+                CfgExpr::Any(_) => unreachable!("disjunction in conjunction"),
+            }
+        }
+
+        Self { literals }
+    }
+}
+
+impl fmt::Display for Conjunction {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.literals.len() != 1 {
+            write!(f, "all(")?;
+        }
+        for (i, lit) in self.literals.iter().enumerate() {
+            if i != 0 {
+                f.write_str(", ")?;
+            }
+
+            write!(f, "{}", lit)?;
+        }
+        if self.literals.len() != 1 {
+            write!(f, ")")?;
+        }
+
+        Ok(())
+    }
+}
+
+impl Literal {
+    fn new(expr: CfgExpr) -> Self {
+        match expr {
+            CfgExpr::Invalid => Self { negate: false, var: None },
+            CfgExpr::Atom(atom) => Self { negate: false, var: Some(atom) },
+            CfgExpr::Not(expr) => match *expr {
+                CfgExpr::Invalid => Self { negate: true, var: None },
+                CfgExpr::Atom(atom) => Self { negate: true, var: Some(atom) },
+                _ => unreachable!("non-atom {:?}", expr),
+            },
+            CfgExpr::Any(_) | CfgExpr::All(_) => unreachable!("non-literal {:?}", expr),
+        }
+    }
+}
+
+impl fmt::Display for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.negate {
+            write!(f, "not(")?;
+        }
+
+        match &self.var {
+            Some(var) => write!(f, "{}", var)?,
+            None => f.write_str("<invalid>")?,
+        }
+
+        if self.negate {
+            write!(f, ")")?;
+        }
+
+        Ok(())
+    }
+}
+
+struct Builder {
+    expr: DnfExpr,
+}
+
+impl Builder {
+    fn lower(mut self, expr: CfgExpr) -> DnfExpr {
+        let expr = make_nnf(expr);
+        let expr = make_dnf(expr);
+
+        match expr {
+            CfgExpr::Invalid | CfgExpr::Atom(_) | CfgExpr::Not(_) => {
+                self.expr.conjunctions.push(Conjunction::new(vec![expr]));
+            }
+            CfgExpr::All(conj) => {
+                self.expr.conjunctions.push(Conjunction::new(conj));
+            }
+            CfgExpr::Any(mut disj) => {
+                disj.reverse();
+                while let Some(conj) = disj.pop() {
+                    match conj {
+                        CfgExpr::Invalid | CfgExpr::Atom(_) | CfgExpr::All(_) | CfgExpr::Not(_) => {
+                            self.expr.conjunctions.push(Conjunction::new(vec![conj]));
+                        }
+                        CfgExpr::Any(inner_disj) => {
+                            // Flatten.
+                            disj.extend(inner_disj.into_iter().rev());
+                        }
+                    }
+                }
+            }
+        }
+
+        self.expr
+    }
+}
+
+fn make_dnf(expr: CfgExpr) -> CfgExpr {
+    match expr {
+        CfgExpr::Invalid | CfgExpr::Atom(_) | CfgExpr::Not(_) => expr,
+        CfgExpr::Any(e) => CfgExpr::Any(e.into_iter().map(|expr| make_dnf(expr)).collect()),
+        CfgExpr::All(e) => {
+            let e = e.into_iter().map(|expr| make_nnf(expr)).collect::<Vec<_>>();
+
+            CfgExpr::Any(distribute_conj(&e))
+        }
+    }
+}
+
+/// Turns a conjunction of expressions into a disjunction of expressions.
+fn distribute_conj(conj: &[CfgExpr]) -> Vec<CfgExpr> {
+    fn go(out: &mut Vec<CfgExpr>, with: &mut Vec<CfgExpr>, rest: &[CfgExpr]) {
+        match rest {
+            [head, tail @ ..] => match head {
+                CfgExpr::Any(disj) => {
+                    for part in disj {
+                        with.push(part.clone());
+                        go(out, with, tail);
+                        with.pop();
+                    }
+                }
+                _ => {
+                    with.push(head.clone());
+                    go(out, with, tail);
+                    with.pop();
+                }
+            },
+            _ => {
+                // Turn accumulated parts into a new conjunction.
+                out.push(CfgExpr::All(with.clone()));
+            }
+        }
+    }
+
+    let mut out = Vec::new();
+    let mut with = Vec::new();
+
+    go(&mut out, &mut with, conj);
+
+    out
+}
+
+fn make_nnf(expr: CfgExpr) -> CfgExpr {
+    match expr {
+        CfgExpr::Invalid | CfgExpr::Atom(_) => expr,
+        CfgExpr::Any(expr) => CfgExpr::Any(expr.into_iter().map(|expr| make_nnf(expr)).collect()),
+        CfgExpr::All(expr) => CfgExpr::All(expr.into_iter().map(|expr| make_nnf(expr)).collect()),
+        CfgExpr::Not(operand) => match *operand {
+            CfgExpr::Invalid | CfgExpr::Atom(_) => CfgExpr::Not(operand.clone()), // Original negated expr
+            CfgExpr::Not(expr) => {
+                // Remove double negation.
+                make_nnf(*expr)
+            }
+            // Convert negated conjunction/disjunction using DeMorgan's Law.
+            CfgExpr::Any(inner) => CfgExpr::All(
+                inner.into_iter().map(|expr| make_nnf(CfgExpr::Not(Box::new(expr)))).collect(),
+            ),
+            CfgExpr::All(inner) => CfgExpr::Any(
+                inner.into_iter().map(|expr| make_nnf(CfgExpr::Not(Box::new(expr)))).collect(),
+            ),
+        },
+    }
+}
diff --git a/crates/cfg/src/lib.rs b/crates/cfg/src/lib.rs
index a9d50e698..d0e08cf5f 100644
--- a/crates/cfg/src/lib.rs
+++ b/crates/cfg/src/lib.rs
@@ -1,11 +1,17 @@
 //! cfg defines conditional compiling options, `cfg` attibute parser and evaluator
 
 mod cfg_expr;
+mod dnf;
+#[cfg(test)]
+mod tests;
+
+use std::fmt;
 
 use rustc_hash::FxHashSet;
 use tt::SmolStr;
 
-pub use cfg_expr::CfgExpr;
+pub use cfg_expr::{CfgAtom, CfgExpr};
+pub use dnf::DnfExpr;
 
 /// Configuration options used for conditional compilition on items with `cfg` attributes.
 /// We have two kind of options in different namespaces: atomic options like `unix`, and
@@ -19,33 +25,131 @@ pub use cfg_expr::CfgExpr;
 /// See: https://doc.rust-lang.org/reference/conditional-compilation.html#set-configuration-options
 #[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub struct CfgOptions {
-    atoms: FxHashSet<SmolStr>,
-    key_values: FxHashSet<(SmolStr, SmolStr)>,
+    enabled: FxHashSet<CfgAtom>,
 }
 
 impl CfgOptions {
     pub fn check(&self, cfg: &CfgExpr) -> Option<bool> {
-        cfg.fold(&|key, value| match value {
-            None => self.atoms.contains(key),
-            Some(value) => self.key_values.contains(&(key.clone(), value.clone())),
-        })
+        cfg.fold(&|atom| self.enabled.contains(atom))
     }
 
     pub fn insert_atom(&mut self, key: SmolStr) {
-        self.atoms.insert(key);
+        self.enabled.insert(CfgAtom::Flag(key));
     }
 
     pub fn insert_key_value(&mut self, key: SmolStr, value: SmolStr) {
-        self.key_values.insert((key, value));
+        self.enabled.insert(CfgAtom::KeyValue { key, value });
     }
 
     pub fn append(&mut self, other: &CfgOptions) {
-        for atom in &other.atoms {
-            self.atoms.insert(atom.clone());
+        for atom in &other.enabled {
+            self.enabled.insert(atom.clone());
+        }
+    }
+
+    pub fn apply_diff(&mut self, diff: CfgDiff) {
+        for atom in diff.enable {
+            self.enabled.insert(atom);
         }
 
-        for (key, value) in &other.key_values {
-            self.key_values.insert((key.clone(), value.clone()));
+        for atom in diff.disable {
+            self.enabled.remove(&atom);
+        }
+    }
+}
+
+pub struct CfgDiff {
+    // Invariants: No duplicates, no atom that's both in `enable` and `disable`.
+    enable: Vec<CfgAtom>,
+    disable: Vec<CfgAtom>,
+}
+
+impl CfgDiff {
+    /// Returns the total number of atoms changed by this diff.
+    pub fn len(&self) -> usize {
+        self.enable.len() + self.disable.len()
+    }
+}
+
+impl fmt::Display for CfgDiff {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if !self.enable.is_empty() {
+            f.write_str("enable ")?;
+            for (i, atom) in self.enable.iter().enumerate() {
+                let sep = match i {
+                    0 => "",
+                    _ if i == self.enable.len() - 1 => " and ",
+                    _ => ", ",
+                };
+                f.write_str(sep)?;
+
+                write!(f, "{}", atom)?;
+            }
+
+            if !self.disable.is_empty() {
+                f.write_str("; ")?;
+            }
         }
+
+        if !self.disable.is_empty() {
+            f.write_str("disable ")?;
+            for (i, atom) in self.disable.iter().enumerate() {
+                let sep = match i {
+                    0 => "",
+                    _ if i == self.enable.len() - 1 => " and ",
+                    _ => ", ",
+                };
+                f.write_str(sep)?;
+
+                write!(f, "{}", atom)?;
+            }
+        }
+
+        Ok(())
+    }
+}
+
+pub struct InactiveReason {
+    enabled: Vec<CfgAtom>,
+    disabled: Vec<CfgAtom>,
+}
+
+impl fmt::Display for InactiveReason {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if !self.enabled.is_empty() {
+            for (i, atom) in self.enabled.iter().enumerate() {
+                let sep = match i {
+                    0 => "",
+                    _ if i == self.enabled.len() - 1 => " and ",
+                    _ => ", ",
+                };
+                f.write_str(sep)?;
+
+                write!(f, "{}", atom)?;
+            }
+            let is_are = if self.enabled.len() == 1 { "is" } else { "are" };
+            write!(f, " {} enabled", is_are)?;
+
+            if !self.disabled.is_empty() {
+                f.write_str(" and ")?;
+            }
+        }
+
+        if !self.disabled.is_empty() {
+            for (i, atom) in self.disabled.iter().enumerate() {
+                let sep = match i {
+                    0 => "",
+                    _ if i == self.disabled.len() - 1 => " and ",
+                    _ => ", ",
+                };
+                f.write_str(sep)?;
+
+                write!(f, "{}", atom)?;
+            }
+            let is_are = if self.disabled.len() == 1 { "is" } else { "are" };
+            write!(f, " {} disabled", is_are)?;
+        }
+
+        Ok(())
     }
 }
diff --git a/crates/cfg/src/tests.rs b/crates/cfg/src/tests.rs
new file mode 100644
index 000000000..bd0f9ec48
--- /dev/null
+++ b/crates/cfg/src/tests.rs
@@ -0,0 +1,193 @@
+use expect_test::{expect, Expect};
+use mbe::ast_to_token_tree;
+use syntax::{ast, AstNode};
+
+use crate::{CfgAtom, CfgExpr, CfgOptions, DnfExpr};
+
+fn assert_parse_result(input: &str, expected: CfgExpr) {
+    let (tt, _) = {
+        let source_file = ast::SourceFile::parse(input).ok().unwrap();
+        let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
+        ast_to_token_tree(&tt).unwrap()
+    };
+    let cfg = CfgExpr::parse(&tt);
+    assert_eq!(cfg, expected);
+}
+
+fn check_dnf(input: &str, expect: Expect) {
+    let (tt, _) = {
+        let source_file = ast::SourceFile::parse(input).ok().unwrap();
+        let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
+        ast_to_token_tree(&tt).unwrap()
+    };
+    let cfg = CfgExpr::parse(&tt);
+    let actual = format!("#![cfg({})]", DnfExpr::new(cfg));
+    expect.assert_eq(&actual);
+}
+
+fn check_why_inactive(input: &str, opts: &CfgOptions, expect: Expect) {
+    let (tt, _) = {
+        let source_file = ast::SourceFile::parse(input).ok().unwrap();
+        let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
+        ast_to_token_tree(&tt).unwrap()
+    };
+    let cfg = CfgExpr::parse(&tt);
+    let dnf = DnfExpr::new(cfg);
+    let why_inactive = dnf.why_inactive(opts).unwrap().to_string();
+    expect.assert_eq(&why_inactive);
+}
+
+#[track_caller]
+fn check_enable_hints(input: &str, opts: &CfgOptions, expected_hints: &[&str]) {
+    let (tt, _) = {
+        let source_file = ast::SourceFile::parse(input).ok().unwrap();
+        let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
+        ast_to_token_tree(&tt).unwrap()
+    };
+    let cfg = CfgExpr::parse(&tt);
+    let dnf = DnfExpr::new(cfg);
+    let hints = dnf.compute_enable_hints(opts).map(|diff| diff.to_string()).collect::<Vec<_>>();
+    assert_eq!(hints, expected_hints);
+}
+
+#[test]
+fn test_cfg_expr_parser() {
+    assert_parse_result("#![cfg(foo)]", CfgAtom::Flag("foo".into()).into());
+    assert_parse_result("#![cfg(foo,)]", CfgAtom::Flag("foo".into()).into());
+    assert_parse_result(
+        "#![cfg(not(foo))]",
+        CfgExpr::Not(Box::new(CfgAtom::Flag("foo".into()).into())),
+    );
+    assert_parse_result("#![cfg(foo(bar))]", CfgExpr::Invalid);
+
+    // Only take the first
+    assert_parse_result(r#"#![cfg(foo, bar = "baz")]"#, CfgAtom::Flag("foo".into()).into());
+
+    assert_parse_result(
+        r#"#![cfg(all(foo, bar = "baz"))]"#,
+        CfgExpr::All(vec![
+            CfgAtom::Flag("foo".into()).into(),
+            CfgAtom::KeyValue { key: "bar".into(), value: "baz".into() }.into(),
+        ]),
+    );
+
+    assert_parse_result(
+        r#"#![cfg(any(not(), all(), , bar = "baz",))]"#,
+        CfgExpr::Any(vec![
+            CfgExpr::Not(Box::new(CfgExpr::Invalid)),
+            CfgExpr::All(vec![]),
+            CfgExpr::Invalid,
+            CfgAtom::KeyValue { key: "bar".into(), value: "baz".into() }.into(),
+        ]),
+    );
+}
+
+#[test]
+fn smoke() {
+    check_dnf("#![cfg(test)]", expect![[r#"#![cfg(test)]"#]]);
+    check_dnf("#![cfg(not(test))]", expect![[r#"#![cfg(not(test))]"#]]);
+    check_dnf("#![cfg(not(not(test)))]", expect![[r#"#![cfg(test)]"#]]);
+
+    check_dnf("#![cfg(all(a, b))]", expect![[r#"#![cfg(all(a, b))]"#]]);
+    check_dnf("#![cfg(any(a, b))]", expect![[r#"#![cfg(any(a, b))]"#]]);
+
+    check_dnf("#![cfg(not(a))]", expect![[r#"#![cfg(not(a))]"#]]);
+}
+
+#[test]
+fn distribute() {
+    check_dnf("#![cfg(all(any(a, b), c))]", expect![[r#"#![cfg(any(all(a, c), all(b, c)))]"#]]);
+    check_dnf("#![cfg(all(c, any(a, b)))]", expect![[r#"#![cfg(any(all(c, a), all(c, b)))]"#]]);
+    check_dnf(
+        "#![cfg(all(any(a, b), any(c, d)))]",
+        expect![[r#"#![cfg(any(all(a, c), all(a, d), all(b, c), all(b, d)))]"#]],
+    );
+
+    check_dnf(
+        "#![cfg(all(any(a, b, c), any(d, e, f), g))]",
+        expect![[
+            r#"#![cfg(any(all(a, d, g), all(a, e, g), all(a, f, g), all(b, d, g), all(b, e, g), all(b, f, g), all(c, d, g), all(c, e, g), all(c, f, g)))]"#
+        ]],
+    );
+}
+
+#[test]
+fn demorgan() {
+    check_dnf("#![cfg(not(all(a, b)))]", expect![[r#"#![cfg(any(not(a), not(b)))]"#]]);
+    check_dnf("#![cfg(not(any(a, b)))]", expect![[r#"#![cfg(all(not(a), not(b)))]"#]]);
+
+    check_dnf("#![cfg(not(all(not(a), b)))]", expect![[r#"#![cfg(any(a, not(b)))]"#]]);
+    check_dnf("#![cfg(not(any(a, not(b))))]", expect![[r#"#![cfg(all(not(a), b))]"#]]);
+}
+
+#[test]
+fn nested() {
+    check_dnf("#![cfg(all(any(a), not(all(any(b)))))]", expect![[r#"#![cfg(all(a, not(b)))]"#]]);
+
+    check_dnf("#![cfg(any(any(a, b)))]", expect![[r#"#![cfg(any(a, b))]"#]]);
+    check_dnf("#![cfg(not(any(any(a, b))))]", expect![[r#"#![cfg(all(not(a), not(b)))]"#]]);
+    check_dnf("#![cfg(all(all(a, b)))]", expect![[r#"#![cfg(all(a, b))]"#]]);
+    check_dnf("#![cfg(not(all(all(a, b))))]", expect![[r#"#![cfg(any(not(a), not(b)))]"#]]);
+}
+
+#[test]
+fn hints() {
+    let mut opts = CfgOptions::default();
+
+    check_enable_hints("#![cfg(test)]", &opts, &["enable test"]);
+    check_enable_hints("#![cfg(not(test))]", &opts, &[]);
+
+    check_enable_hints("#![cfg(any(a, b))]", &opts, &["enable a", "enable b"]);
+    check_enable_hints("#![cfg(any(b, a))]", &opts, &["enable b", "enable a"]);
+
+    check_enable_hints("#![cfg(all(a, b))]", &opts, &["enable a and b"]);
+
+    opts.insert_atom("test".into());
+
+    check_enable_hints("#![cfg(test)]", &opts, &[]);
+    check_enable_hints("#![cfg(not(test))]", &opts, &["disable test"]);
+}
+
+/// Tests that we don't suggest hints for cfgs that express an inconsistent formula.
+#[test]
+fn hints_impossible() {
+    let mut opts = CfgOptions::default();
+
+    check_enable_hints("#![cfg(all(test, not(test)))]", &opts, &[]);
+
+    opts.insert_atom("test".into());
+
+    check_enable_hints("#![cfg(all(test, not(test)))]", &opts, &[]);
+}
+
+#[test]
+fn why_inactive() {
+    let mut opts = CfgOptions::default();
+    opts.insert_atom("test".into());
+    opts.insert_atom("test2".into());
+
+    check_why_inactive("#![cfg(a)]", &opts, expect![["a is disabled"]]);
+    check_why_inactive("#![cfg(not(test))]", &opts, expect![["test is enabled"]]);
+
+    check_why_inactive(
+        "#![cfg(all(not(test), not(test2)))]",
+        &opts,
+        expect![["test and test2 are enabled"]],
+    );
+    check_why_inactive("#![cfg(all(a, b))]", &opts, expect![["a and b are disabled"]]);
+    check_why_inactive(
+        "#![cfg(all(not(test), a))]",
+        &opts,
+        expect![["test is enabled and a is disabled"]],
+    );
+    check_why_inactive(
+        "#![cfg(all(not(test), test2, a))]",
+        &opts,
+        expect![["test is enabled and a is disabled"]],
+    );
+    check_why_inactive(
+        "#![cfg(all(not(test), not(test2), a))]",
+        &opts,
+        expect![["test and test2 are enabled and a is disabled"]],
+    );
+}
diff --git a/crates/completion/Cargo.toml b/crates/completion/Cargo.toml
index 25192456a..b79ee33f7 100644
--- a/crates/completion/Cargo.toml
+++ b/crates/completion/Cargo.toml
@@ -21,8 +21,6 @@ base_db = { path = "../base_db", version = "0.0.0" }
 ide_db = { path = "../ide_db", version = "0.0.0" }
 profile = { path = "../profile", version = "0.0.0" }
 test_utils = { path = "../test_utils", version = "0.0.0" }
-assists = { path = "../assists", version = "0.0.0" }
-call_info = { path = "../call_info", version = "0.0.0" }
 
 # completions crate should depend only on the top-level `hir` package. if you need
 # something from some `hir_xxx` subpackage, reexport the API via `hir`.
diff --git a/crates/completion/src/complete_mod.rs b/crates/completion/src/complete_mod.rs
index 35a57aba3..385911afa 100644
--- a/crates/completion/src/complete_mod.rs
+++ b/crates/completion/src/complete_mod.rs
@@ -1,7 +1,7 @@
 //! Completes mod declarations.
 
-use base_db::{SourceDatabaseExt, VfsPath};
 use hir::{Module, ModuleSource};
+use ide_db::base_db::{SourceDatabaseExt, VfsPath};
 use ide_db::RootDatabase;
 use rustc_hash::FxHashSet;
 
diff --git a/crates/completion/src/complete_postfix.rs b/crates/completion/src/complete_postfix.rs
index 700573cf2..2622f12ab 100644
--- a/crates/completion/src/complete_postfix.rs
+++ b/crates/completion/src/complete_postfix.rs
@@ -2,7 +2,7 @@
 
 mod format_like;
 
-use assists::utils::TryEnum;
+use ide_db::ty_filter::TryEnum;
 use syntax::{
     ast::{self, AstNode, AstToken},
     TextRange, TextSize,
diff --git a/crates/completion/src/complete_trait_impl.rs b/crates/completion/src/complete_trait_impl.rs
index c06af99e2..a14be9c73 100644
--- a/crates/completion/src/complete_trait_impl.rs
+++ b/crates/completion/src/complete_trait_impl.rs
@@ -31,8 +31,8 @@
 //! }
 //! ```
 
-use assists::utils::get_missing_assoc_items;
 use hir::{self, HasAttrs, HasSource};
+use ide_db::traits::get_missing_assoc_items;
 use syntax::{
     ast::{self, edit, Impl},
     display::function_declaration,
diff --git a/crates/completion/src/completion_context.rs b/crates/completion/src/completion_context.rs
index e4f86d0e0..dca304a8f 100644
--- a/crates/completion/src/completion_context.rs
+++ b/crates/completion/src/completion_context.rs
@@ -1,9 +1,8 @@
 //! See `CompletionContext` structure.
 
-use base_db::{FilePosition, SourceDatabase};
-use call_info::ActiveParameter;
 use hir::{Local, ScopeDef, Semantics, SemanticsScope, Type};
-use ide_db::RootDatabase;
+use ide_db::base_db::{FilePosition, SourceDatabase};
+use ide_db::{call_info::ActiveParameter, RootDatabase};
 use syntax::{
     algo::{find_covering_element, find_node_at_offset},
     ast, match_ast, AstNode, NodeOrToken,
diff --git a/crates/completion/src/lib.rs b/crates/completion/src/lib.rs
index 0a60ea7f2..b72fd249d 100644
--- a/crates/completion/src/lib.rs
+++ b/crates/completion/src/lib.rs
@@ -23,7 +23,7 @@ mod complete_macro_in_item_position;
 mod complete_trait_impl;
 mod complete_mod;
 
-use base_db::FilePosition;
+use ide_db::base_db::FilePosition;
 use ide_db::RootDatabase;
 
 use crate::{
diff --git a/crates/completion/src/presentation.rs b/crates/completion/src/presentation.rs
index 2a19281cf..0a6f5a1ea 100644
--- a/crates/completion/src/presentation.rs
+++ b/crates/completion/src/presentation.rs
@@ -304,9 +304,14 @@ impl Completions {
     ) {
         let is_deprecated = is_deprecated(variant, ctx.db);
         let name = local_name.unwrap_or_else(|| variant.name(ctx.db).to_string());
-        let qualified_name = match &path {
-            Some(it) => it.to_string(),
-            None => name.to_string(),
+        let (qualified_name, short_qualified_name) = match &path {
+            Some(path) => {
+                let full = path.to_string();
+                let short =
+                    path.segments[path.segments.len().saturating_sub(2)..].iter().join("::");
+                (full, short)
+            }
+            None => (name.to_string(), name.to_string()),
         };
         let detail_types = variant
             .fields(ctx.db)
@@ -335,14 +340,12 @@ impl Completions {
         .set_deprecated(is_deprecated)
         .detail(detail);
 
-        if path.is_some() {
-            res = res.lookup_by(name);
-        }
-
         if variant_kind == StructKind::Tuple {
             mark::hit!(inserts_parens_for_tuple_enums);
             let params = Params::Anonymous(variant.fields(ctx.db).len());
-            res = res.add_call_parens(ctx, qualified_name, params)
+            res = res.add_call_parens(ctx, short_qualified_name, params)
+        } else if path.is_some() {
+            res = res.lookup_by(short_qualified_name);
         }
 
         res.add_to(self);
@@ -607,6 +610,57 @@ fn main() { Foo::Fo<|> }
     }
 
     #[test]
+    fn lookup_enums_by_two_qualifiers() {
+        check(
+            r#"
+mod m {
+    pub enum Spam { Foo, Bar(i32) }
+}
+fn main() { let _: m::Spam = S<|> }
+"#,
+            expect![[r#"
+                [
+                    CompletionItem {
+                        label: "Spam::Bar(…)",
+                        source_range: 75..76,
+                        delete: 75..76,
+                        insert: "Spam::Bar($0)",
+                        kind: EnumVariant,
+                        lookup: "Spam::Bar",
+                        detail: "(i32)",
+                        trigger_call_info: true,
+                    },
+                    CompletionItem {
+                        label: "m",
+                        source_range: 75..76,
+                        delete: 75..76,
+                        insert: "m",
+                        kind: Module,
+                    },
+                    CompletionItem {
+                        label: "m::Spam::Foo",
+                        source_range: 75..76,
+                        delete: 75..76,
+                        insert: "m::Spam::Foo",
+                        kind: EnumVariant,
+                        lookup: "Spam::Foo",
+                        detail: "()",
+                    },
+                    CompletionItem {
+                        label: "main()",
+                        source_range: 75..76,
+                        delete: 75..76,
+                        insert: "main()$0",
+                        kind: Function,
+                        lookup: "main",
+                        detail: "fn main()",
+                    },
+                ]
+            "#]],
+        )
+    }
+
+    #[test]
     fn sets_deprecated_flag_in_completion_items() {
         check(
             r#"
diff --git a/crates/completion/src/test_utils.rs b/crates/completion/src/test_utils.rs
index f2cf2561f..b02556797 100644
--- a/crates/completion/src/test_utils.rs
+++ b/crates/completion/src/test_utils.rs
@@ -1,7 +1,7 @@
 //! Runs completion for testing purposes.
 
-use base_db::{fixture::ChangeFixture, FileLoader, FilePosition};
 use hir::Semantics;
+use ide_db::base_db::{fixture::ChangeFixture, FileLoader, FilePosition};
 use ide_db::RootDatabase;
 use itertools::Itertools;
 use stdx::{format_to, trim_indent};
diff --git a/crates/hir/src/code_model.rs b/crates/hir/src/code_model.rs
index 7f169ccd2..63c1a8ebf 100644
--- a/crates/hir/src/code_model.rs
+++ b/crates/hir/src/code_model.rs
@@ -31,8 +31,7 @@ use hir_ty::{
     autoderef,
     display::{HirDisplayError, HirFormatter},
     method_resolution,
-    traits::Solution,
-    traits::SolutionVariables,
+    traits::{FnTrait, Solution, SolutionVariables},
     ApplicationTy, BoundVar, CallableDefId, Canonical, DebruijnIndex, FnSig, GenericPredicate,
     InEnvironment, Obligation, ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment, Ty,
     TyDefId, TyKind, TypeCtor,
@@ -781,6 +780,7 @@ impl Function {
     }
 
     pub fn diagnostics(self, db: &dyn HirDatabase, sink: &mut DiagnosticSink) {
+        hir_def::diagnostics::validate_body(db.upcast(), self.id.into(), sink);
         hir_ty::diagnostics::validate_module_item(db, self.id.into(), sink);
         hir_ty::diagnostics::validate_body(db, self.id.into(), sink);
     }
@@ -1385,6 +1385,28 @@ impl Type {
         )
     }
 
+    /// Checks that particular type `ty` implements `std::ops::FnOnce`.
+    ///
+    /// This function can be used to check if a particular type is callable, since FnOnce is a
+    /// supertrait of Fn and FnMut, so all callable types implements at least FnOnce.
+    pub fn impls_fnonce(&self, db: &dyn HirDatabase) -> bool {
+        let krate = self.krate;
+
+        let fnonce_trait = match FnTrait::FnOnce.get_id(db, krate) {
+            Some(it) => it,
+            None => return false,
+        };
+
+        let canonical_ty = Canonical { value: self.ty.value.clone(), kinds: Arc::new([]) };
+        method_resolution::implements_trait(
+            &canonical_ty,
+            db,
+            self.ty.environment.clone(),
+            krate,
+            fnonce_trait,
+        )
+    }
+
     pub fn impls_trait(&self, db: &dyn HirDatabase, trait_: Trait, args: &[Type]) -> bool {
         let trait_ref = hir_ty::TraitRef {
             trait_: trait_.id,
diff --git a/crates/hir_def/src/attr.rs b/crates/hir_def/src/attr.rs
index dea552a60..b2ce7ca3c 100644
--- a/crates/hir_def/src/attr.rs
+++ b/crates/hir_def/src/attr.rs
@@ -125,12 +125,20 @@ impl Attrs {
         AttrQuery { attrs: self, key }
     }
 
-    pub fn cfg(&self) -> impl Iterator<Item = CfgExpr> + '_ {
+    pub fn cfg(&self) -> Option<CfgExpr> {
         // FIXME: handle cfg_attr :-)
-        self.by_key("cfg").tt_values().map(CfgExpr::parse)
+        let mut cfgs = self.by_key("cfg").tt_values().map(CfgExpr::parse).collect::<Vec<_>>();
+        match cfgs.len() {
+            0 => None,
+            1 => Some(cfgs.pop().unwrap()),
+            _ => Some(CfgExpr::All(cfgs)),
+        }
     }
     pub(crate) fn is_cfg_enabled(&self, cfg_options: &CfgOptions) -> bool {
-        self.cfg().all(|cfg| cfg_options.check(&cfg) != Some(false))
+        match self.cfg() {
+            None => true,
+            Some(cfg) => cfg_options.check(&cfg) != Some(false),
+        }
     }
 }
 
diff --git a/crates/hir_def/src/body.rs b/crates/hir_def/src/body.rs
index d51036e4f..d10b1af01 100644
--- a/crates/hir_def/src/body.rs
+++ b/crates/hir_def/src/body.rs
@@ -1,6 +1,9 @@
 //! Defines `Body`: a lowered representation of bodies of functions, statics and
 //! consts.
 mod lower;
+mod diagnostics;
+#[cfg(test)]
+mod tests;
 pub mod scope;
 
 use std::{mem, ops::Index, sync::Arc};
@@ -10,7 +13,10 @@ use base_db::CrateId;
 use cfg::CfgOptions;
 use drop_bomb::DropBomb;
 use either::Either;
-use hir_expand::{ast_id_map::AstIdMap, hygiene::Hygiene, AstId, HirFileId, InFile, MacroDefId};
+use hir_expand::{
+    ast_id_map::AstIdMap, diagnostics::DiagnosticSink, hygiene::Hygiene, AstId, HirFileId, InFile,
+    MacroDefId,
+};
 use rustc_hash::FxHashMap;
 use syntax::{ast, AstNode, AstPtr};
 use test_utils::mark;
@@ -150,8 +156,12 @@ impl Expander {
         InFile { file_id: self.current_file_id, value }
     }
 
-    pub(crate) fn is_cfg_enabled(&self, owner: &dyn ast::AttrsOwner) -> bool {
-        self.cfg_expander.is_cfg_enabled(owner)
+    pub(crate) fn parse_attrs(&self, owner: &dyn ast::AttrsOwner) -> Attrs {
+        self.cfg_expander.parse_attrs(owner)
+    }
+
+    pub(crate) fn cfg_options(&self) -> &CfgOptions {
+        &self.cfg_expander.cfg_options
     }
 
     fn parse_path(&mut self, path: ast::Path) -> Option<Path> {
@@ -219,6 +229,10 @@ pub struct BodySourceMap {
     pat_map_back: ArenaMap<PatId, Result<PatSource, SyntheticSyntax>>,
     field_map: FxHashMap<(ExprId, usize), InFile<AstPtr<ast::RecordExprField>>>,
     expansions: FxHashMap<InFile<AstPtr<ast::MacroCall>>, HirFileId>,
+
+    /// Diagnostics accumulated during body lowering. These contain `AstPtr`s and so are stored in
+    /// the source map (since they're just as volatile).
+    diagnostics: Vec<diagnostics::BodyDiagnostic>,
 }
 
 #[derive(Default, Debug, Eq, PartialEq, Clone, Copy)]
@@ -318,45 +332,10 @@ impl BodySourceMap {
     pub fn field_syntax(&self, expr: ExprId, field: usize) -> InFile<AstPtr<ast::RecordExprField>> {
         self.field_map[&(expr, field)].clone()
     }
-}
-
-#[cfg(test)]
-mod tests {
-    use base_db::{fixture::WithFixture, SourceDatabase};
-    use test_utils::mark;
 
-    use crate::ModuleDefId;
-
-    use super::*;
-
-    fn lower(ra_fixture: &str) -> Arc<Body> {
-        let (db, file_id) = crate::test_db::TestDB::with_single_file(ra_fixture);
-
-        let krate = db.crate_graph().iter().next().unwrap();
-        let def_map = db.crate_def_map(krate);
-        let module = def_map.modules_for_file(file_id).next().unwrap();
-        let module = &def_map[module];
-        let fn_def = match module.scope.declarations().next().unwrap() {
-            ModuleDefId::FunctionId(it) => it,
-            _ => panic!(),
-        };
-
-        db.body(fn_def.into())
-    }
-
-    #[test]
-    fn your_stack_belongs_to_me() {
-        mark::check!(your_stack_belongs_to_me);
-        lower(
-            "
-macro_rules! n_nuple {
-    ($e:tt) => ();
-    ($($rest:tt)*) => {{
-        (n_nuple!($($rest)*)None,)
-    }};
-}
-fn main() { n_nuple!(1,2,3); }
-",
-        );
+    pub(crate) fn add_diagnostics(&self, _db: &dyn DefDatabase, sink: &mut DiagnosticSink<'_>) {
+        for diag in &self.diagnostics {
+            diag.add_to(sink);
+        }
     }
 }
diff --git a/crates/hir_def/src/body/diagnostics.rs b/crates/hir_def/src/body/diagnostics.rs
new file mode 100644
index 000000000..cfa47d189
--- /dev/null
+++ b/crates/hir_def/src/body/diagnostics.rs
@@ -0,0 +1,20 @@
+//! Diagnostics emitted during body lowering.
+
+use hir_expand::diagnostics::DiagnosticSink;
+
+use crate::diagnostics::InactiveCode;
+
+#[derive(Debug, Eq, PartialEq)]
+pub enum BodyDiagnostic {
+    InactiveCode(InactiveCode),
+}
+
+impl BodyDiagnostic {
+    pub fn add_to(&self, sink: &mut DiagnosticSink<'_>) {
+        match self {
+            BodyDiagnostic::InactiveCode(diag) => {
+                sink.push(diag.clone());
+            }
+        }
+    }
+}
diff --git a/crates/hir_def/src/body/lower.rs b/crates/hir_def/src/body/lower.rs
index 01e72690a..ddc267b83 100644
--- a/crates/hir_def/src/body/lower.rs
+++ b/crates/hir_def/src/body/lower.rs
@@ -16,7 +16,7 @@ use syntax::{
         self, ArgListOwner, ArrayExprKind, AstChildren, LiteralKind, LoopBodyOwner, NameOwner,
         SlicePatComponents,
     },
-    AstNode, AstPtr,
+    AstNode, AstPtr, SyntaxNodePtr,
 };
 use test_utils::mark;
 
@@ -25,6 +25,7 @@ use crate::{
     body::{Body, BodySourceMap, Expander, PatPtr, SyntheticSyntax},
     builtin_type::{BuiltinFloat, BuiltinInt},
     db::DefDatabase,
+    diagnostics::InactiveCode,
     expr::{
         dummy_expr_id, ArithOp, Array, BinaryOp, BindingAnnotation, CmpOp, Expr, ExprId, Literal,
         LogicOp, MatchArm, Ordering, Pat, PatId, RecordFieldPat, RecordLitField, Statement,
@@ -37,7 +38,7 @@ use crate::{
     StaticLoc, StructLoc, TraitLoc, TypeAliasLoc, UnionLoc,
 };
 
-use super::{ExprSource, PatSource};
+use super::{diagnostics::BodyDiagnostic, ExprSource, PatSource};
 
 pub(crate) struct LowerCtx {
     hygiene: Hygiene,
@@ -176,7 +177,7 @@ impl ExprCollector<'_> {
 
     fn collect_expr(&mut self, expr: ast::Expr) -> ExprId {
         let syntax_ptr = AstPtr::new(&expr);
-        if !self.expander.is_cfg_enabled(&expr) {
+        if self.check_cfg(&expr).is_none() {
             return self.missing_expr();
         }
 
@@ -354,13 +355,15 @@ impl ExprCollector<'_> {
                 let arms = if let Some(match_arm_list) = e.match_arm_list() {
                     match_arm_list
                         .arms()
-                        .map(|arm| MatchArm {
-                            pat: self.collect_pat_opt(arm.pat()),
-                            expr: self.collect_expr_opt(arm.expr()),
-                            guard: arm
-                                .guard()
-                                .and_then(|guard| guard.expr())
-                                .map(|e| self.collect_expr(e)),
+                        .filter_map(|arm| {
+                            self.check_cfg(&arm).map(|()| MatchArm {
+                                pat: self.collect_pat_opt(arm.pat()),
+                                expr: self.collect_expr_opt(arm.expr()),
+                                guard: arm
+                                    .guard()
+                                    .and_then(|guard| guard.expr())
+                                    .map(|e| self.collect_expr(e)),
+                            })
                         })
                         .collect()
                 } else {
@@ -406,9 +409,8 @@ impl ExprCollector<'_> {
                         .fields()
                         .inspect(|field| field_ptrs.push(AstPtr::new(field)))
                         .filter_map(|field| {
-                            if !self.expander.is_cfg_enabled(&field) {
-                                return None;
-                            }
+                            self.check_cfg(&field)?;
+
                             let name = field.field_name()?.as_name();
 
                             Some(RecordLitField {
@@ -620,15 +622,23 @@ impl ExprCollector<'_> {
             .filter_map(|s| {
                 let stmt = match s {
                     ast::Stmt::LetStmt(stmt) => {
+                        self.check_cfg(&stmt)?;
+
                         let pat = self.collect_pat_opt(stmt.pat());
                         let type_ref = stmt.ty().map(|it| TypeRef::from_ast(&self.ctx(), it));
                         let initializer = stmt.initializer().map(|e| self.collect_expr(e));
                         Statement::Let { pat, type_ref, initializer }
                     }
                     ast::Stmt::ExprStmt(stmt) => {
+                        self.check_cfg(&stmt)?;
+
                         Statement::Expr(self.collect_expr_opt(stmt.expr()))
                     }
-                    ast::Stmt::Item(_) => return None,
+                    ast::Stmt::Item(item) => {
+                        self.check_cfg(&item)?;
+
+                        return None;
+                    }
                 };
                 Some(stmt)
             })
@@ -872,6 +882,28 @@ impl ExprCollector<'_> {
 
         (args, ellipsis)
     }
+
+    /// Returns `None` (and emits diagnostics) when `owner` if `#[cfg]`d out, and `Some(())` when
+    /// not.
+    fn check_cfg(&mut self, owner: &dyn ast::AttrsOwner) -> Option<()> {
+        match self.expander.parse_attrs(owner).cfg() {
+            Some(cfg) => {
+                if self.expander.cfg_options().check(&cfg) != Some(false) {
+                    return Some(());
+                }
+
+                self.source_map.diagnostics.push(BodyDiagnostic::InactiveCode(InactiveCode {
+                    file: self.expander.current_file_id,
+                    node: SyntaxNodePtr::new(owner.syntax()),
+                    cfg,
+                    opts: self.expander.cfg_options().clone(),
+                }));
+
+                None
+            }
+            None => Some(()),
+        }
+    }
 }
 
 impl From<ast::BinOp> for BinaryOp {
diff --git a/crates/hir_def/src/body/tests.rs b/crates/hir_def/src/body/tests.rs
new file mode 100644
index 000000000..f07df5cee
--- /dev/null
+++ b/crates/hir_def/src/body/tests.rs
@@ -0,0 +1,75 @@
+use base_db::{fixture::WithFixture, SourceDatabase};
+use test_utils::mark;
+
+use crate::{test_db::TestDB, ModuleDefId};
+
+use super::*;
+
+fn lower(ra_fixture: &str) -> Arc<Body> {
+    let (db, file_id) = crate::test_db::TestDB::with_single_file(ra_fixture);
+
+    let krate = db.crate_graph().iter().next().unwrap();
+    let def_map = db.crate_def_map(krate);
+    let module = def_map.modules_for_file(file_id).next().unwrap();
+    let module = &def_map[module];
+    let fn_def = match module.scope.declarations().next().unwrap() {
+        ModuleDefId::FunctionId(it) => it,
+        _ => panic!(),
+    };
+
+    db.body(fn_def.into())
+}
+
+fn check_diagnostics(ra_fixture: &str) {
+    let db: TestDB = TestDB::with_files(ra_fixture);
+    db.check_diagnostics();
+}
+
+#[test]
+fn your_stack_belongs_to_me() {
+    mark::check!(your_stack_belongs_to_me);
+    lower(
+        "
+macro_rules! n_nuple {
+    ($e:tt) => ();
+    ($($rest:tt)*) => {{
+        (n_nuple!($($rest)*)None,)
+    }};
+}
+fn main() { n_nuple!(1,2,3); }
+",
+    );
+}
+
+#[test]
+fn cfg_diagnostics() {
+    check_diagnostics(
+        r"
+fn f() {
+    // The three g̶e̶n̶d̶e̶r̶s̶ statements:
+
+    #[cfg(a)] fn f() {}  // Item statement
+  //^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    #[cfg(a)] {}         // Expression statement
+  //^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    #[cfg(a)] let x = 0; // let statement
+  //^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+
+    abc(#[cfg(a)] 0);
+      //^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    let x = Struct {
+        #[cfg(a)] f: 0,
+      //^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    };
+    match () {
+        () => (),
+        #[cfg(a)] () => (),
+      //^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    }
+
+    #[cfg(a)] 0          // Trailing expression of block
+  //^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+}
+    ",
+    );
+}
diff --git a/crates/hir_def/src/diagnostics.rs b/crates/hir_def/src/diagnostics.rs
index c9c08b01f..b221b290c 100644
--- a/crates/hir_def/src/diagnostics.rs
+++ b/crates/hir_def/src/diagnostics.rs
@@ -1,11 +1,19 @@
 //! Diagnostics produced by `hir_def`.
 
 use std::any::Any;
+use stdx::format_to;
 
-use hir_expand::diagnostics::{Diagnostic, DiagnosticCode};
+use cfg::{CfgExpr, CfgOptions, DnfExpr};
+use hir_expand::diagnostics::{Diagnostic, DiagnosticCode, DiagnosticSink};
+use hir_expand::{HirFileId, InFile};
 use syntax::{ast, AstPtr, SyntaxNodePtr};
 
-use hir_expand::{HirFileId, InFile};
+use crate::{db::DefDatabase, DefWithBodyId};
+
+pub fn validate_body(db: &dyn DefDatabase, owner: DefWithBodyId, sink: &mut DiagnosticSink<'_>) {
+    let source_map = db.body_with_source_map(owner).1;
+    source_map.add_diagnostics(db, sink);
+}
 
 // Diagnostic: unresolved-module
 //
@@ -87,13 +95,15 @@ impl Diagnostic for UnresolvedImport {
     }
 }
 
-// Diagnostic: unconfigured-code
+// Diagnostic: inactive-code
 //
 // This diagnostic is shown for code with inactive `#[cfg]` attributes.
-#[derive(Debug)]
+#[derive(Debug, Clone, Eq, PartialEq)]
 pub struct InactiveCode {
     pub file: HirFileId,
     pub node: SyntaxNodePtr,
+    pub cfg: CfgExpr,
+    pub opts: CfgOptions,
 }
 
 impl Diagnostic for InactiveCode {
@@ -101,8 +111,14 @@ impl Diagnostic for InactiveCode {
         DiagnosticCode("inactive-code")
     }
     fn message(&self) -> String {
-        // FIXME: say *why* it is configured out
-        "code is inactive due to #[cfg] directives".to_string()
+        let inactive = DnfExpr::new(self.cfg.clone()).why_inactive(&self.opts);
+        let mut buf = "code is inactive due to #[cfg] directives".to_string();
+
+        if let Some(inactive) = inactive {
+            format_to!(buf, ": {}", inactive);
+        }
+
+        buf
     }
     fn display_source(&self) -> InFile<SyntaxNodePtr> {
         InFile::new(self.file, self.node.clone())
diff --git a/crates/hir_def/src/nameres.rs b/crates/hir_def/src/nameres.rs
index 01a28aeeb..eb41d324e 100644
--- a/crates/hir_def/src/nameres.rs
+++ b/crates/hir_def/src/nameres.rs
@@ -283,6 +283,7 @@ pub enum ModuleSource {
 }
 
 mod diagnostics {
+    use cfg::{CfgExpr, CfgOptions};
     use hir_expand::diagnostics::DiagnosticSink;
     use hir_expand::hygiene::Hygiene;
     use hir_expand::InFile;
@@ -299,7 +300,7 @@ mod diagnostics {
 
         UnresolvedImport { ast: AstId<ast::Use>, index: usize },
 
-        UnconfiguredCode { ast: InFile<SyntaxNodePtr> },
+        UnconfiguredCode { ast: InFile<SyntaxNodePtr>, cfg: CfgExpr, opts: CfgOptions },
     }
 
     #[derive(Debug, PartialEq, Eq)]
@@ -341,8 +342,10 @@ mod diagnostics {
         pub(super) fn unconfigured_code(
             container: LocalModuleId,
             ast: InFile<SyntaxNodePtr>,
+            cfg: CfgExpr,
+            opts: CfgOptions,
         ) -> Self {
-            Self { in_module: container, kind: DiagnosticKind::UnconfiguredCode { ast } }
+            Self { in_module: container, kind: DiagnosticKind::UnconfiguredCode { ast, cfg, opts } }
         }
 
         pub(super) fn add_to(
@@ -395,8 +398,13 @@ mod diagnostics {
                     }
                 }
 
-                DiagnosticKind::UnconfiguredCode { ast } => {
-                    sink.push(InactiveCode { file: ast.file_id, node: ast.value.clone() });
+                DiagnosticKind::UnconfiguredCode { ast, cfg, opts } => {
+                    sink.push(InactiveCode {
+                        file: ast.file_id,
+                        node: ast.value.clone(),
+                        cfg: cfg.clone(),
+                        opts: opts.clone(),
+                    });
                 }
             }
         }
diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index bff8edb62..f30172d90 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -6,7 +6,7 @@
 use std::iter;
 
 use base_db::{CrateId, FileId, ProcMacroId};
-use cfg::CfgOptions;
+use cfg::{CfgExpr, CfgOptions};
 use hir_expand::InFile;
 use hir_expand::{
     ast_id_map::FileAstId,
@@ -900,7 +900,8 @@ impl ModCollector<'_, '_> {
         // `#[macro_use] extern crate` is hoisted to imports macros before collecting
         // any other items.
         for item in items {
-            if self.is_cfg_enabled(self.item_tree.attrs((*item).into())) {
+            let attrs = self.item_tree.attrs((*item).into());
+            if attrs.cfg().map_or(true, |cfg| self.is_cfg_enabled(&cfg)) {
                 if let ModItem::ExternCrate(id) = item {
                     let import = self.item_tree[*id].clone();
                     if import.is_macro_use {
@@ -912,9 +913,11 @@ impl ModCollector<'_, '_> {
 
         for &item in items {
             let attrs = self.item_tree.attrs(item.into());
-            if !self.is_cfg_enabled(attrs) {
-                self.emit_unconfigured_diagnostic(item);
-                continue;
+            if let Some(cfg) = attrs.cfg() {
+                if !self.is_cfg_enabled(&cfg) {
+                    self.emit_unconfigured_diagnostic(item, &cfg);
+                    continue;
+                }
             }
             let module =
                 ModuleId { krate: self.def_collector.def_map.krate, local_id: self.module_id };
@@ -1321,20 +1324,22 @@ impl ModCollector<'_, '_> {
         }
     }
 
-    fn is_cfg_enabled(&self, attrs: &Attrs) -> bool {
-        attrs.is_cfg_enabled(self.def_collector.cfg_options)
+    fn is_cfg_enabled(&self, cfg: &CfgExpr) -> bool {
+        self.def_collector.cfg_options.check(cfg) != Some(false)
     }
 
-    fn emit_unconfigured_diagnostic(&mut self, item: ModItem) {
+    fn emit_unconfigured_diagnostic(&mut self, item: ModItem, cfg: &CfgExpr) {
         let ast_id = item.ast_id(self.item_tree);
         let id_map = self.def_collector.db.ast_id_map(self.file_id);
         let syntax_ptr = id_map.get(ast_id).syntax_node_ptr();
 
         let ast_node = InFile::new(self.file_id, syntax_ptr);
-        self.def_collector
-            .def_map
-            .diagnostics
-            .push(DefDiagnostic::unconfigured_code(self.module_id, ast_node));
+        self.def_collector.def_map.diagnostics.push(DefDiagnostic::unconfigured_code(
+            self.module_id,
+            ast_node,
+            cfg.clone(),
+            self.def_collector.cfg_options.clone(),
+        ));
     }
 }
 
diff --git a/crates/hir_def/src/nameres/tests/diagnostics.rs b/crates/hir_def/src/nameres/tests/diagnostics.rs
index 576b813d2..1a7b98831 100644
--- a/crates/hir_def/src/nameres/tests/diagnostics.rs
+++ b/crates/hir_def/src/nameres/tests/diagnostics.rs
@@ -1,42 +1,10 @@
 use base_db::fixture::WithFixture;
-use base_db::FileId;
-use base_db::SourceDatabaseExt;
-use hir_expand::db::AstDatabase;
-use rustc_hash::FxHashMap;
-use syntax::TextRange;
-use syntax::TextSize;
 
 use crate::test_db::TestDB;
 
 fn check_diagnostics(ra_fixture: &str) {
     let db: TestDB = TestDB::with_files(ra_fixture);
-    let annotations = db.extract_annotations();
-    assert!(!annotations.is_empty());
-
-    let mut actual: FxHashMap<FileId, Vec<(TextRange, String)>> = FxHashMap::default();
-    db.diagnostics(|d| {
-        let src = d.display_source();
-        let root = db.parse_or_expand(src.file_id).unwrap();
-        // FIXME: macros...
-        let file_id = src.file_id.original_file(&db);
-        let range = src.value.to_node(&root).text_range();
-        let message = d.message().to_owned();
-        actual.entry(file_id).or_default().push((range, message));
-    });
-
-    for (file_id, diags) in actual.iter_mut() {
-        diags.sort_by_key(|it| it.0.start());
-        let text = db.file_text(*file_id);
-        // For multiline spans, place them on line start
-        for (range, content) in diags {
-            if text[*range].contains('\n') {
-                *range = TextRange::new(range.start(), range.start() + TextSize::from(1));
-                *content = format!("... {}", content);
-            }
-        }
-    }
-
-    assert_eq!(annotations, actual);
+    db.check_diagnostics();
 }
 
 #[test]
@@ -129,3 +97,25 @@ fn unresolved_module() {
         ",
     );
 }
+
+#[test]
+fn inactive_item() {
+    // Additional tests in `cfg` crate. This only tests disabled cfgs.
+
+    check_diagnostics(
+        r#"
+        //- /lib.rs
+          #[cfg(no)] pub fn f() {}
+        //^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: no is disabled
+
+          #[cfg(no)] #[cfg(no2)] mod m;
+        //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: no and no2 are disabled
+
+          #[cfg(all(not(a), b))] enum E {}
+        //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: b is disabled
+
+          #[cfg(feature = "std")] use std;
+        //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: feature = "std" is disabled
+        "#,
+    );
+}
diff --git a/crates/hir_def/src/test_db.rs b/crates/hir_def/src/test_db.rs
index fb1d3c974..2b36c824a 100644
--- a/crates/hir_def/src/test_db.rs
+++ b/crates/hir_def/src/test_db.rs
@@ -12,10 +12,10 @@ use hir_expand::diagnostics::Diagnostic;
 use hir_expand::diagnostics::DiagnosticSinkBuilder;
 use rustc_hash::FxHashMap;
 use rustc_hash::FxHashSet;
-use syntax::TextRange;
+use syntax::{TextRange, TextSize};
 use test_utils::extract_annotations;
 
-use crate::db::DefDatabase;
+use crate::{db::DefDatabase, ModuleDefId};
 
 #[salsa::database(
     base_db::SourceDatabaseExtStorage,
@@ -135,9 +135,47 @@ impl TestDB {
             let crate_def_map = self.crate_def_map(krate);
 
             let mut sink = DiagnosticSinkBuilder::new().build(&mut cb);
-            for (module_id, _) in crate_def_map.modules.iter() {
+            for (module_id, module) in crate_def_map.modules.iter() {
                 crate_def_map.add_diagnostics(self, module_id, &mut sink);
+
+                for decl in module.scope.declarations() {
+                    if let ModuleDefId::FunctionId(it) = decl {
+                        let source_map = self.body_with_source_map(it.into()).1;
+                        source_map.add_diagnostics(self, &mut sink);
+                    }
+                }
             }
         }
     }
+
+    pub fn check_diagnostics(&self) {
+        let db: &TestDB = self;
+        let annotations = db.extract_annotations();
+        assert!(!annotations.is_empty());
+
+        let mut actual: FxHashMap<FileId, Vec<(TextRange, String)>> = FxHashMap::default();
+        db.diagnostics(|d| {
+            let src = d.display_source();
+            let root = db.parse_or_expand(src.file_id).unwrap();
+            // FIXME: macros...
+            let file_id = src.file_id.original_file(db);
+            let range = src.value.to_node(&root).text_range();
+            let message = d.message().to_owned();
+            actual.entry(file_id).or_default().push((range, message));
+        });
+
+        for (file_id, diags) in actual.iter_mut() {
+            diags.sort_by_key(|it| it.0.start());
+            let text = db.file_text(*file_id);
+            // For multiline spans, place them on line start
+            for (range, content) in diags {
+                if text[*range].contains('\n') {
+                    *range = TextRange::new(range.start(), range.start() + TextSize::from(1));
+                    *content = format!("... {}", content);
+                }
+            }
+        }
+
+        assert_eq!(annotations, actual);
+    }
 }
diff --git a/crates/hir_ty/Cargo.toml b/crates/hir_ty/Cargo.toml
index e9c62c6aa..367a1b98d 100644
--- a/crates/hir_ty/Cargo.toml
+++ b/crates/hir_ty/Cargo.toml
@@ -17,9 +17,9 @@ ena = "0.14.0"
 log = "0.4.8"
 rustc-hash = "1.1.0"
 scoped-tls = "1"
-chalk-solve = "0.33"
-chalk-ir = "0.33"
-chalk-recursive = "0.33"
+chalk-solve = { version = "0.34", default-features = false }
+chalk-ir = "0.34"
+chalk-recursive = "0.34"
 
 stdx = { path = "../stdx", version = "0.0.0" }
 hir_def = { path = "../hir_def", version = "0.0.0" }
diff --git a/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs b/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
index 324d60765..b0144a289 100644
--- a/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
+++ b/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
@@ -1,156 +1,145 @@
 //! Functions for string case manipulation, such as detecting the identifier case,
 //! and converting it into appropriate form.
 
-#[derive(Debug)]
-enum DetectedCase {
-    LowerCamelCase,
-    UpperCamelCase,
-    LowerSnakeCase,
-    UpperSnakeCase,
-    Unknown,
-}
-
-fn detect_case(ident: &str) -> DetectedCase {
-    let trimmed_ident = ident.trim_matches('_');
-    let first_lowercase = trimmed_ident.starts_with(|chr: char| chr.is_ascii_lowercase());
-    let mut has_lowercase = first_lowercase;
-    let mut has_uppercase = false;
-    let mut has_underscore = false;
-
-    for chr in trimmed_ident.chars() {
-        if chr == '_' {
-            has_underscore = true;
-        } else if chr.is_ascii_uppercase() {
-            has_uppercase = true;
-        } else if chr.is_ascii_lowercase() {
-            has_lowercase = true;
-        }
-    }
-
-    if has_uppercase {
-        if !has_lowercase {
-            if has_underscore {
-                DetectedCase::UpperSnakeCase
-            } else {
-                // It has uppercase only and no underscores. Ex: "AABB"
-                // This is a camel cased acronym.
-                DetectedCase::UpperCamelCase
-            }
-        } else if !has_underscore {
-            if first_lowercase {
-                DetectedCase::LowerCamelCase
-            } else {
-                DetectedCase::UpperCamelCase
-            }
-        } else {
-            // It has uppercase, it has lowercase, it has underscore.
-            // No assumptions here
-            DetectedCase::Unknown
-        }
-    } else {
-        DetectedCase::LowerSnakeCase
-    }
-}
+// Code that was taken from rustc was taken at commit 89fdb30,
+// from file /compiler/rustc_lint/src/nonstandard_style.rs
 
 /// Converts an identifier to an UpperCamelCase form.
 /// Returns `None` if the string is already is UpperCamelCase.
 pub fn to_camel_case(ident: &str) -> Option<String> {
-    let detected_case = detect_case(ident);
-
-    match detected_case {
-        DetectedCase::UpperCamelCase => return None,
-        DetectedCase::LowerCamelCase => {
-            let mut first_capitalized = false;
-            let output = ident
-                .chars()
-                .map(|chr| {
-                    if !first_capitalized && chr.is_ascii_lowercase() {
-                        first_capitalized = true;
-                        chr.to_ascii_uppercase()
-                    } else {
-                        chr
-                    }
-                })
-                .collect();
-            return Some(output);
-        }
-        _ => {}
+    if is_camel_case(ident) {
+        return None;
     }
 
-    let mut output = String::with_capacity(ident.len());
-
-    let mut capital_added = false;
-    for chr in ident.chars() {
-        if chr.is_alphabetic() {
-            if !capital_added {
-                output.push(chr.to_ascii_uppercase());
-                capital_added = true;
-            } else {
-                output.push(chr.to_ascii_lowercase());
+    // Taken from rustc.
+    let ret = ident
+        .trim_matches('_')
+        .split('_')
+        .filter(|component| !component.is_empty())
+        .map(|component| {
+            let mut camel_cased_component = String::new();
+
+            let mut new_word = true;
+            let mut prev_is_lower_case = true;
+
+            for c in component.chars() {
+                // Preserve the case if an uppercase letter follows a lowercase letter, so that
+                // `camelCase` is converted to `CamelCase`.
+                if prev_is_lower_case && c.is_uppercase() {
+                    new_word = true;
+                }
+
+                if new_word {
+                    camel_cased_component.push_str(&c.to_uppercase().to_string());
+                } else {
+                    camel_cased_component.push_str(&c.to_lowercase().to_string());
+                }
+
+                prev_is_lower_case = c.is_lowercase();
+                new_word = false;
             }
-        } else if chr == '_' {
-            // Skip this character and make the next one capital.
-            capital_added = false;
-        } else {
-            // Put the characted as-is.
-            output.push(chr);
-        }
-    }
 
-    if output == ident {
-        // While we didn't detect the correct case at the beginning, there
-        // may be special cases: e.g. `A` is both valid CamelCase and UPPER_SNAKE_CASE.
-        None
-    } else {
-        Some(output)
-    }
+            camel_cased_component
+        })
+        .fold((String::new(), None), |(acc, prev): (String, Option<String>), next| {
+            // separate two components with an underscore if their boundary cannot
+            // be distinguished using a uppercase/lowercase case distinction
+            let join = if let Some(prev) = prev {
+                let l = prev.chars().last().unwrap();
+                let f = next.chars().next().unwrap();
+                !char_has_case(l) && !char_has_case(f)
+            } else {
+                false
+            };
+            (acc + if join { "_" } else { "" } + &next, Some(next))
+        })
+        .0;
+    Some(ret)
 }
 
 /// Converts an identifier to a lower_snake_case form.
 /// Returns `None` if the string is already in lower_snake_case.
 pub fn to_lower_snake_case(ident: &str) -> Option<String> {
-    // First, assume that it's UPPER_SNAKE_CASE.
-    match detect_case(ident) {
-        DetectedCase::LowerSnakeCase => return None,
-        DetectedCase::UpperSnakeCase => {
-            return Some(ident.chars().map(|chr| chr.to_ascii_lowercase()).collect())
-        }
-        _ => {}
+    if is_lower_snake_case(ident) {
+        return None;
+    } else if is_upper_snake_case(ident) {
+        return Some(ident.to_lowercase());
     }
 
-    // Otherwise, assume that it's CamelCase.
-    let lower_snake_case = stdx::to_lower_snake_case(ident);
-
-    if lower_snake_case == ident {
-        // While we didn't detect the correct case at the beginning, there
-        // may be special cases: e.g. `a` is both valid camelCase and snake_case.
-        None
-    } else {
-        Some(lower_snake_case)
-    }
+    Some(stdx::to_lower_snake_case(ident))
 }
 
 /// Converts an identifier to an UPPER_SNAKE_CASE form.
 /// Returns `None` if the string is already is UPPER_SNAKE_CASE.
 pub fn to_upper_snake_case(ident: &str) -> Option<String> {
-    match detect_case(ident) {
-        DetectedCase::UpperSnakeCase => return None,
-        DetectedCase::LowerSnakeCase => {
-            return Some(ident.chars().map(|chr| chr.to_ascii_uppercase()).collect())
-        }
-        _ => {}
+    if is_upper_snake_case(ident) {
+        return None;
+    } else if is_lower_snake_case(ident) {
+        return Some(ident.to_uppercase());
+    }
+
+    Some(stdx::to_upper_snake_case(ident))
+}
+
+// Taken from rustc.
+// Modified by replacing the use of unstable feature `array_windows`.
+fn is_camel_case(name: &str) -> bool {
+    let name = name.trim_matches('_');
+    if name.is_empty() {
+        return true;
     }
 
-    // Normalize the string from whatever form it's in currently, and then just make it uppercase.
-    let upper_snake_case = stdx::to_upper_snake_case(ident);
+    let mut fst = None;
+    // start with a non-lowercase letter rather than non-uppercase
+    // ones (some scripts don't have a concept of upper/lowercase)
+    !name.chars().next().unwrap().is_lowercase()
+        && !name.contains("__")
+        && !name.chars().any(|snd| {
+            let ret = match (fst, snd) {
+                (None, _) => false,
+                (Some(fst), snd) => {
+                    char_has_case(fst) && snd == '_' || char_has_case(snd) && fst == '_'
+                }
+            };
+            fst = Some(snd);
+
+            ret
+        })
+}
+
+fn is_lower_snake_case(ident: &str) -> bool {
+    is_snake_case(ident, char::is_uppercase)
+}
 
-    if upper_snake_case == ident {
-        // While we didn't detect the correct case at the beginning, there
-        // may be special cases: e.g. `A` is both valid CamelCase and UPPER_SNAKE_CASE.
-        None
-    } else {
-        Some(upper_snake_case)
+fn is_upper_snake_case(ident: &str) -> bool {
+    is_snake_case(ident, char::is_lowercase)
+}
+
+// Taken from rustc.
+// Modified to allow checking for both upper and lower snake case.
+fn is_snake_case<F: Fn(char) -> bool>(ident: &str, wrong_case: F) -> bool {
+    if ident.is_empty() {
+        return true;
     }
+    let ident = ident.trim_matches('_');
+
+    let mut allow_underscore = true;
+    ident.chars().all(|c| {
+        allow_underscore = match c {
+            '_' if !allow_underscore => return false,
+            '_' => false,
+            // It would be more obvious to check for the correct case,
+            // but some characters do not have a case.
+            c if !wrong_case(c) => true,
+            _ => return false,
+        };
+        true
+    })
+}
+
+// Taken from rustc.
+fn char_has_case(c: char) -> bool {
+    c.is_lowercase() || c.is_uppercase()
 }
 
 #[cfg(test)]
@@ -173,6 +162,7 @@ mod tests {
         check(to_lower_snake_case, "CamelCase", expect![["camel_case"]]);
         check(to_lower_snake_case, "lowerCamelCase", expect![["lower_camel_case"]]);
         check(to_lower_snake_case, "a", expect![[""]]);
+        check(to_lower_snake_case, "abc", expect![[""]]);
     }
 
     #[test]
@@ -187,6 +177,11 @@ mod tests {
         check(to_camel_case, "name", expect![["Name"]]);
         check(to_camel_case, "A", expect![[""]]);
         check(to_camel_case, "AABB", expect![[""]]);
+        // Taken from rustc: /compiler/rustc_lint/src/nonstandard_style/tests.rs
+        check(to_camel_case, "X86_64", expect![[""]]);
+        check(to_camel_case, "x86__64", expect![["X86_64"]]);
+        check(to_camel_case, "Abc_123", expect![["Abc123"]]);
+        check(to_camel_case, "A1_b2_c3", expect![["A1B2C3"]]);
     }
 
     #[test]
@@ -197,5 +192,7 @@ mod tests {
         check(to_upper_snake_case, "CamelCase", expect![["CAMEL_CASE"]]);
         check(to_upper_snake_case, "lowerCamelCase", expect![["LOWER_CAMEL_CASE"]]);
         check(to_upper_snake_case, "A", expect![[""]]);
+        check(to_upper_snake_case, "ABC", expect![[""]]);
+        check(to_upper_snake_case, "X86_64", expect![[""]]);
     }
 }
diff --git a/crates/hir_ty/src/traits.rs b/crates/hir_ty/src/traits.rs
index 14cd3a2b4..ce1174cbe 100644
--- a/crates/hir_ty/src/traits.rs
+++ b/crates/hir_ty/src/traits.rs
@@ -5,6 +5,7 @@ use base_db::CrateId;
 use chalk_ir::cast::Cast;
 use chalk_solve::{logging_db::LoggingRustIrDatabase, Solver};
 use hir_def::{lang_item::LangItemTarget, TraitId};
+use stdx::panic_context;
 
 use crate::{db::HirDatabase, DebruijnIndex, Substs};
 
@@ -168,14 +169,23 @@ fn solve(
     };
 
     let mut solve = || {
-        if is_chalk_print() {
-            let logging_db = LoggingRustIrDatabase::new(context);
-            let solution = solver.solve_limited(&logging_db, goal, &should_continue);
-            log::debug!("chalk program:\n{}", logging_db);
+        let _ctx = if is_chalk_debug() || is_chalk_print() {
+            Some(panic_context::enter(format!("solving {:?}", goal)))
+        } else {
+            None
+        };
+        let solution = if is_chalk_print() {
+            let logging_db =
+                LoggingRustIrDatabaseLoggingOnDrop(LoggingRustIrDatabase::new(context));
+            let solution = solver.solve_limited(&logging_db.0, goal, &should_continue);
             solution
         } else {
             solver.solve_limited(&context, goal, &should_continue)
-        }
+        };
+
+        log::debug!("solve({:?}) => {:?}", goal, solution);
+
+        solution
     };
 
     // don't set the TLS for Chalk unless Chalk debugging is active, to make
@@ -183,11 +193,17 @@ fn solve(
     let solution =
         if is_chalk_debug() { chalk::tls::set_current_program(db, solve) } else { solve() };
 
-    log::debug!("solve({:?}) => {:?}", goal, solution);
-
     solution
 }
 
+struct LoggingRustIrDatabaseLoggingOnDrop<'a>(LoggingRustIrDatabase<Interner, ChalkContext<'a>>);
+
+impl<'a> Drop for LoggingRustIrDatabaseLoggingOnDrop<'a> {
+    fn drop(&mut self) {
+        eprintln!("chalk program:\n{}", self.0);
+    }
+}
+
 fn is_chalk_debug() -> bool {
     std::env::var("CHALK_DEBUG").is_ok()
 }
diff --git a/crates/hir_ty/src/traits/chalk/mapping.rs b/crates/hir_ty/src/traits/chalk/mapping.rs
index be3301313..dd7affcec 100644
--- a/crates/hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/hir_ty/src/traits/chalk/mapping.rs
@@ -4,8 +4,8 @@
 //! conversions.
 
 use chalk_ir::{
-    cast::Cast, fold::shift::Shift, interner::HasInterner, PlaceholderIndex, Scalar, TypeName,
-    UniverseIndex,
+    cast::Cast, fold::shift::Shift, interner::HasInterner, LifetimeData, PlaceholderIndex, Scalar,
+    TypeName, UniverseIndex,
 };
 use chalk_solve::rust_ir;
 
@@ -76,7 +76,7 @@ impl ToChalk for Ty {
                 );
                 let bounded_ty = chalk_ir::DynTy {
                     bounds: make_binders(where_clauses, 1),
-                    lifetime: FAKE_PLACEHOLDER.to_lifetime(&Interner),
+                    lifetime: LifetimeData::Static.intern(&Interner),
                 };
                 chalk_ir::TyData::Dyn(bounded_ty).intern(&Interner)
             }
@@ -161,9 +161,6 @@ impl ToChalk for Ty {
     }
 }
 
-const FAKE_PLACEHOLDER: PlaceholderIndex =
-    PlaceholderIndex { ui: UniverseIndex::ROOT, idx: usize::MAX };
-
 /// We currently don't model lifetimes, but Chalk does. So, we have to insert a
 /// fake lifetime here, because Chalks built-in logic may expect it to be there.
 fn ref_to_chalk(
@@ -172,7 +169,7 @@ fn ref_to_chalk(
     subst: Substs,
 ) -> chalk_ir::Ty<Interner> {
     let arg = subst[0].clone().to_chalk(db);
-    let lifetime = FAKE_PLACEHOLDER.to_lifetime(&Interner);
+    let lifetime = LifetimeData::Static.intern(&Interner);
     chalk_ir::ApplicationTy {
         name: TypeName::Ref(mutability.to_chalk(db)),
         substitution: chalk_ir::Substitution::from_iter(
@@ -205,7 +202,11 @@ fn array_to_chalk(db: &dyn HirDatabase, subst: Substs) -> chalk_ir::Ty<Interner>
         substitution: chalk_ir::Substitution::empty(&Interner),
     }
     .intern(&Interner);
-    let const_ = FAKE_PLACEHOLDER.to_const(&Interner, usize_ty);
+    let const_ = chalk_ir::ConstData {
+        ty: usize_ty,
+        value: chalk_ir::ConstValue::Concrete(chalk_ir::ConcreteConst { interned: () }),
+    }
+    .intern(&Interner);
     chalk_ir::ApplicationTy {
         name: TypeName::Array,
         substitution: chalk_ir::Substitution::from_iter(
diff --git a/crates/ide/Cargo.toml b/crates/ide/Cargo.toml
index 63299dc31..4d483580d 100644
--- a/crates/ide/Cargo.toml
+++ b/crates/ide/Cargo.toml
@@ -11,7 +11,7 @@ doctest = false
 
 [dependencies]
 either = "1.5.3"
-indexmap = "1.3.2"
+indexmap = "1.4.0"
 itertools = "0.9.0"
 log = "0.4.8"
 rustc-hash = "1.1.0"
@@ -23,14 +23,12 @@ url = "2.1.1"
 stdx = { path = "../stdx", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
 text_edit = { path = "../text_edit", version = "0.0.0" }
-base_db = { path = "../base_db", version = "0.0.0" }
 ide_db = { path = "../ide_db", version = "0.0.0" }
 cfg = { path = "../cfg", version = "0.0.0" }
 profile = { path = "../profile", version = "0.0.0" }
 test_utils = { path = "../test_utils", version = "0.0.0" }
 assists = { path = "../assists", version = "0.0.0" }
 ssr = { path = "../ssr", version = "0.0.0" }
-call_info = { path = "../call_info", version = "0.0.0" }
 completion = { path = "../completion", version = "0.0.0" }
 
 # ide should depend only on the top-level `hir` package. if you need
diff --git a/crates/ide/src/call_hierarchy.rs b/crates/ide/src/call_hierarchy.rs
index 9d6433fe0..8ad50a2ee 100644
--- a/crates/ide/src/call_hierarchy.rs
+++ b/crates/ide/src/call_hierarchy.rs
@@ -2,8 +2,8 @@
 
 use indexmap::IndexMap;
 
-use call_info::FnCallNode;
 use hir::Semantics;
+use ide_db::call_info::FnCallNode;
 use ide_db::RootDatabase;
 use syntax::{ast, match_ast, AstNode, TextRange};
 
@@ -137,7 +137,7 @@ impl CallLocations {
 
 #[cfg(test)]
 mod tests {
-    use base_db::FilePosition;
+    use ide_db::base_db::FilePosition;
 
     use crate::fixture;
 
diff --git a/crates/ide/src/diagnostics.rs b/crates/ide/src/diagnostics.rs
index 90574cb35..d0ee58858 100644
--- a/crates/ide/src/diagnostics.rs
+++ b/crates/ide/src/diagnostics.rs
@@ -9,11 +9,11 @@ mod field_shorthand;
 
 use std::cell::RefCell;
 
-use base_db::SourceDatabase;
 use hir::{
     diagnostics::{Diagnostic as _, DiagnosticSinkBuilder},
     Semantics,
 };
+use ide_db::base_db::SourceDatabase;
 use ide_db::RootDatabase;
 use itertools::Itertools;
 use rustc_hash::FxHashSet;
@@ -613,7 +613,7 @@ fn main() {
 pub struct Foo { pub a: i32, pub b: i32 }
 "#,
             r#"
-fn {a:42, b: ()} {}
+fn some(, b: ()} {}
 fn items() {}
 fn here() {}
 
diff --git a/crates/ide/src/diagnostics/field_shorthand.rs b/crates/ide/src/diagnostics/field_shorthand.rs
index 54e9fce9e..f41bcd619 100644
--- a/crates/ide/src/diagnostics/field_shorthand.rs
+++ b/crates/ide/src/diagnostics/field_shorthand.rs
@@ -1,7 +1,7 @@
 //! Suggests shortening `Foo { field: field }` to `Foo { field }` in both
 //! expressions and patterns.
 
-use base_db::FileId;
+use ide_db::base_db::FileId;
 use ide_db::source_change::SourceFileEdit;
 use syntax::{ast, match_ast, AstNode, SyntaxNode};
 use text_edit::TextEdit;
diff --git a/crates/ide/src/diagnostics/fixes.rs b/crates/ide/src/diagnostics/fixes.rs
index 0c75e50b0..0c950003e 100644
--- a/crates/ide/src/diagnostics/fixes.rs
+++ b/crates/ide/src/diagnostics/fixes.rs
@@ -1,6 +1,5 @@
 //! Provides a way to attach fixes to the diagnostics.
 //! The same module also has all curret custom fixes for the diagnostics implemented.
-use base_db::FileId;
 use hir::{
     db::AstDatabase,
     diagnostics::{
@@ -9,6 +8,7 @@ use hir::{
     },
     HasSource, HirDisplay, Semantics, VariantDef,
 };
+use ide_db::base_db::FileId;
 use ide_db::{
     source_change::{FileSystemEdit, SourceFileEdit},
     RootDatabase,
diff --git a/crates/ide/src/display/navigation_target.rs b/crates/ide/src/display/navigation_target.rs
index cf9d617dc..0c429a262 100644
--- a/crates/ide/src/display/navigation_target.rs
+++ b/crates/ide/src/display/navigation_target.rs
@@ -1,8 +1,8 @@
 //! FIXME: write short doc here
 
-use base_db::{FileId, SourceDatabase};
 use either::Either;
 use hir::{original_range, AssocItem, FieldSource, HasSource, InFile, ModuleSource};
+use ide_db::base_db::{FileId, SourceDatabase};
 use ide_db::{defs::Definition, RootDatabase};
 use syntax::{
     ast::{self, DocCommentsOwner, NameOwner},
diff --git a/crates/ide/src/fixture.rs b/crates/ide/src/fixture.rs
index ed06689f0..eb57f9224 100644
--- a/crates/ide/src/fixture.rs
+++ b/crates/ide/src/fixture.rs
@@ -1,5 +1,5 @@
 //! Utilities for creating `Analysis` instances for tests.
-use base_db::fixture::ChangeFixture;
+use ide_db::base_db::fixture::ChangeFixture;
 use test_utils::{extract_annotations, RangeOrOffset};
 
 use crate::{Analysis, AnalysisHost, FileId, FilePosition, FileRange};
diff --git a/crates/ide/src/goto_definition.rs b/crates/ide/src/goto_definition.rs
index a87e31019..15792f947 100644
--- a/crates/ide/src/goto_definition.rs
+++ b/crates/ide/src/goto_definition.rs
@@ -100,7 +100,7 @@ pub(crate) fn reference_definition(
 
 #[cfg(test)]
 mod tests {
-    use base_db::FileRange;
+    use ide_db::base_db::FileRange;
     use syntax::{TextRange, TextSize};
 
     use crate::fixture;
diff --git a/crates/ide/src/goto_implementation.rs b/crates/ide/src/goto_implementation.rs
index 6c586bbd1..529004878 100644
--- a/crates/ide/src/goto_implementation.rs
+++ b/crates/ide/src/goto_implementation.rs
@@ -74,7 +74,7 @@ fn impls_for_trait(
 
 #[cfg(test)]
 mod tests {
-    use base_db::FileRange;
+    use ide_db::base_db::FileRange;
 
     use crate::fixture;
 
diff --git a/crates/ide/src/goto_type_definition.rs b/crates/ide/src/goto_type_definition.rs
index 6d0df04dd..aba6bf5dc 100644
--- a/crates/ide/src/goto_type_definition.rs
+++ b/crates/ide/src/goto_type_definition.rs
@@ -54,7 +54,7 @@ fn pick_best(tokens: TokenAtOffset<SyntaxToken>) -> Option<SyntaxToken> {
 
 #[cfg(test)]
 mod tests {
-    use base_db::FileRange;
+    use ide_db::base_db::FileRange;
 
     use crate::fixture;
 
diff --git a/crates/ide/src/hover.rs b/crates/ide/src/hover.rs
index 6466422c5..832192881 100644
--- a/crates/ide/src/hover.rs
+++ b/crates/ide/src/hover.rs
@@ -1,8 +1,8 @@
-use base_db::SourceDatabase;
 use hir::{
     Adt, AsAssocItem, AssocItemContainer, Documentation, FieldSource, HasSource, HirDisplay,
     Module, ModuleDef, ModuleSource, Semantics,
 };
+use ide_db::base_db::SourceDatabase;
 use ide_db::{
     defs::{Definition, NameClass, NameRefClass},
     RootDatabase,
@@ -385,8 +385,8 @@ fn pick_best(tokens: TokenAtOffset<SyntaxToken>) -> Option<SyntaxToken> {
 
 #[cfg(test)]
 mod tests {
-    use base_db::FileLoader;
     use expect_test::{expect, Expect};
+    use ide_db::base_db::FileLoader;
 
     use crate::fixture;
 
@@ -638,6 +638,33 @@ fn main() { }
     }
 
     #[test]
+    fn hover_shows_fn_doc_attr_raw_string() {
+        check(
+            r##"
+#[doc = r#"Raw string doc attr"#]
+pub fn foo<|>(_: &Path) {}
+
+fn main() { }
+"##,
+            expect![[r##"
+                *foo*
+
+                ```rust
+                test
+                ```
+
+                ```rust
+                pub fn foo(_: &Path)
+                ```
+
+                ---
+
+                Raw string doc attr
+            "##]],
+        );
+    }
+
+    #[test]
     fn hover_shows_struct_field_info() {
         // Hovering over the field when instantiating
         check(
@@ -2128,7 +2155,7 @@ fn foo_<|>test() {}
                                     ignore: false,
                                 },
                             },
-                            cfg_exprs: [],
+                            cfg: None,
                         },
                     ),
                 ]
@@ -2166,7 +2193,7 @@ mod tests<|> {
                             kind: TestMod {
                                 path: "tests",
                             },
-                            cfg_exprs: [],
+                            cfg: None,
                         },
                     ),
                 ]
diff --git a/crates/ide/src/lib.rs b/crates/ide/src/lib.rs
index cecfae4c7..4bc733b70 100644
--- a/crates/ide/src/lib.rs
+++ b/crates/ide/src/lib.rs
@@ -48,11 +48,11 @@ mod doc_links;
 
 use std::sync::Arc;
 
-use base_db::{
+use cfg::CfgOptions;
+use ide_db::base_db::{
     salsa::{self, ParallelDatabase},
     CheckCanceled, Env, FileLoader, FileSet, SourceDatabase, VfsPath,
 };
-use cfg::CfgOptions;
 use ide_db::{
     symbol_index::{self, FileSymbol},
     LineIndexDatabase,
@@ -80,19 +80,19 @@ pub use crate::{
         Highlight, HighlightModifier, HighlightModifiers, HighlightTag, HighlightedRange,
     },
 };
-pub use call_info::CallInfo;
 pub use completion::{
     CompletionConfig, CompletionItem, CompletionItemKind, CompletionScore, InsertTextFormat,
 };
+pub use ide_db::call_info::CallInfo;
 
 pub use assists::{
     utils::MergeBehaviour, Assist, AssistConfig, AssistId, AssistKind, ResolvedAssist,
 };
-pub use base_db::{
+pub use hir::{Documentation, Semantics};
+pub use ide_db::base_db::{
     Canceled, Change, CrateGraph, CrateId, Edition, FileId, FilePosition, FileRange, SourceRoot,
     SourceRootId,
 };
-pub use hir::{Documentation, Semantics};
 pub use ide_db::{
     label::Label,
     line_index::{LineCol, LineIndex},
@@ -396,7 +396,7 @@ impl Analysis {
 
     /// Computes parameter information for the given call expression.
     pub fn call_info(&self, position: FilePosition) -> Cancelable<Option<CallInfo>> {
-        self.with_db(|db| call_info::call_info(db, position))
+        self.with_db(|db| ide_db::call_info::call_info(db, position))
     }
 
     /// Computes call hierarchy candidates for the given file position.
diff --git a/crates/ide/src/parent_module.rs b/crates/ide/src/parent_module.rs
index ef94acfec..6cc3b2991 100644
--- a/crates/ide/src/parent_module.rs
+++ b/crates/ide/src/parent_module.rs
@@ -1,5 +1,5 @@
-use base_db::{CrateId, FileId, FilePosition};
 use hir::Semantics;
+use ide_db::base_db::{CrateId, FileId, FilePosition};
 use ide_db::RootDatabase;
 use syntax::{
     algo::find_node_at_offset,
diff --git a/crates/ide/src/prime_caches.rs b/crates/ide/src/prime_caches.rs
index 6944dbcd2..ea0acfaa0 100644
--- a/crates/ide/src/prime_caches.rs
+++ b/crates/ide/src/prime_caches.rs
@@ -3,8 +3,8 @@
 //! request takes longer to compute. This modules implemented prepopulating of
 //! various caches, it's not really advanced at the moment.
 
-use base_db::SourceDatabase;
 use hir::db::DefDatabase;
+use ide_db::base_db::SourceDatabase;
 
 use crate::RootDatabase;
 
diff --git a/crates/ide/src/references.rs b/crates/ide/src/references.rs
index 67ec257a8..a517081d5 100644
--- a/crates/ide/src/references.rs
+++ b/crates/ide/src/references.rs
@@ -191,8 +191,8 @@ fn get_struct_def_name_for_struct_literal_search(
 
 #[cfg(test)]
 mod tests {
-    use base_db::FileId;
     use expect_test::{expect, Expect};
+    use ide_db::base_db::FileId;
     use stdx::format_to;
 
     use crate::{fixture, SearchScope};
diff --git a/crates/ide/src/references/rename.rs b/crates/ide/src/references/rename.rs
index 35aafc49d..26ac2371a 100644
--- a/crates/ide/src/references/rename.rs
+++ b/crates/ide/src/references/rename.rs
@@ -1,7 +1,7 @@
 //! FIXME: write short doc here
 
-use base_db::SourceDatabaseExt;
 use hir::{Module, ModuleDef, ModuleSource, Semantics};
+use ide_db::base_db::SourceDatabaseExt;
 use ide_db::{
     defs::{Definition, NameClass, NameRefClass},
     RootDatabase,
diff --git a/crates/ide/src/runnables.rs b/crates/ide/src/runnables.rs
index 752ef2f21..eb82456ad 100644
--- a/crates/ide/src/runnables.rs
+++ b/crates/ide/src/runnables.rs
@@ -15,7 +15,7 @@ use crate::{display::ToNav, FileId, NavigationTarget};
 pub struct Runnable {
     pub nav: NavigationTarget,
     pub kind: RunnableKind,
-    pub cfg_exprs: Vec<CfgExpr>,
+    pub cfg: Option<CfgExpr>,
 }
 
 #[derive(Debug, Clone)]
@@ -168,7 +168,7 @@ fn runnable_fn(
     };
 
     let attrs = Attrs::from_attrs_owner(sema.db, InFile::new(HirFileId::from(file_id), &fn_def));
-    let cfg_exprs = attrs.cfg().collect();
+    let cfg = attrs.cfg();
 
     let nav = if let RunnableKind::DocTest { .. } = kind {
         NavigationTarget::from_doc_commented(
@@ -179,7 +179,7 @@ fn runnable_fn(
     } else {
         NavigationTarget::from_named(sema.db, InFile::new(file_id.into(), &fn_def))
     };
-    Some(Runnable { nav, kind, cfg_exprs })
+    Some(Runnable { nav, kind, cfg })
 }
 
 #[derive(Debug, Copy, Clone)]
@@ -255,9 +255,9 @@ fn runnable_mod(
         .join("::");
 
     let attrs = Attrs::from_attrs_owner(sema.db, InFile::new(HirFileId::from(file_id), &module));
-    let cfg_exprs = attrs.cfg().collect();
+    let cfg = attrs.cfg();
     let nav = module_def.to_nav(sema.db);
-    Some(Runnable { nav, kind: RunnableKind::TestMod { path }, cfg_exprs })
+    Some(Runnable { nav, kind: RunnableKind::TestMod { path }, cfg })
 }
 
 // We could create runnables for modules with number_of_test_submodules > 0,
@@ -348,7 +348,7 @@ fn bench() {}
                             docs: None,
                         },
                         kind: Bin,
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -373,7 +373,7 @@ fn bench() {}
                                 ignore: false,
                             },
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -398,7 +398,7 @@ fn bench() {}
                                 ignore: true,
                             },
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -420,7 +420,7 @@ fn bench() {}
                                 "bench",
                             ),
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                 ]
             "#]],
@@ -507,7 +507,7 @@ fn should_have_no_runnable_6() {}
                             docs: None,
                         },
                         kind: Bin,
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -527,7 +527,7 @@ fn should_have_no_runnable_6() {}
                                 "should_have_runnable",
                             ),
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -547,7 +547,7 @@ fn should_have_no_runnable_6() {}
                                 "should_have_runnable_1",
                             ),
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -567,7 +567,7 @@ fn should_have_no_runnable_6() {}
                                 "should_have_runnable_2",
                             ),
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                 ]
             "#]],
@@ -609,7 +609,7 @@ impl Data {
                             docs: None,
                         },
                         kind: Bin,
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -629,7 +629,7 @@ impl Data {
                                 "Data::foo",
                             ),
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                 ]
             "#]],
@@ -668,7 +668,7 @@ mod test_mod {
                         kind: TestMod {
                             path: "test_mod",
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -693,7 +693,7 @@ mod test_mod {
                                 ignore: false,
                             },
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                 ]
             "#]],
@@ -748,7 +748,7 @@ mod root_tests {
                         kind: TestMod {
                             path: "root_tests::nested_tests_0",
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -768,7 +768,7 @@ mod root_tests {
                         kind: TestMod {
                             path: "root_tests::nested_tests_0::nested_tests_1",
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -793,7 +793,7 @@ mod root_tests {
                                 ignore: false,
                             },
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -818,7 +818,7 @@ mod root_tests {
                                 ignore: false,
                             },
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -838,7 +838,7 @@ mod root_tests {
                         kind: TestMod {
                             path: "root_tests::nested_tests_0::nested_tests_2",
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                     Runnable {
                         nav: NavigationTarget {
@@ -863,7 +863,7 @@ mod root_tests {
                                 ignore: false,
                             },
                         },
-                        cfg_exprs: [],
+                        cfg: None,
                     },
                 ]
             "#]],
@@ -906,12 +906,14 @@ fn test_foo1() {}
                                 ignore: false,
                             },
                         },
-                        cfg_exprs: [
-                            KeyValue {
-                                key: "feature",
-                                value: "foo",
-                            },
-                        ],
+                        cfg: Some(
+                            Atom(
+                                KeyValue {
+                                    key: "feature",
+                                    value: "foo",
+                                },
+                            ),
+                        ),
                     },
                 ]
             "#]],
@@ -954,20 +956,24 @@ fn test_foo1() {}
                                 ignore: false,
                             },
                         },
-                        cfg_exprs: [
+                        cfg: Some(
                             All(
                                 [
-                                    KeyValue {
-                                        key: "feature",
-                                        value: "foo",
-                                    },
-                                    KeyValue {
-                                        key: "feature",
-                                        value: "bar",
-                                    },
+                                    Atom(
+                                        KeyValue {
+                                            key: "feature",
+                                            value: "foo",
+                                        },
+                                    ),
+                                    Atom(
+                                        KeyValue {
+                                            key: "feature",
+                                            value: "bar",
+                                        },
+                                    ),
                                 ],
                             ),
-                        ],
+                        ),
                     },
                 ]
             "#]],
diff --git a/crates/ide/src/status.rs b/crates/ide/src/status.rs
index 0af84daa0..8e91c99d7 100644
--- a/crates/ide/src/status.rs
+++ b/crates/ide/src/status.rs
@@ -1,10 +1,10 @@
 use std::{fmt, iter::FromIterator, sync::Arc};
 
-use base_db::{
+use hir::MacroFile;
+use ide_db::base_db::{
     salsa::debug::{DebugQueryTable, TableEntry},
     CrateId, FileId, FileTextQuery, SourceDatabase, SourceRootId,
 };
-use hir::MacroFile;
 use ide_db::{
     symbol_index::{LibrarySymbolsQuery, SymbolIndex},
     RootDatabase,
@@ -16,7 +16,7 @@ use stdx::format_to;
 use syntax::{ast, Parse, SyntaxNode};
 
 fn syntax_tree_stats(db: &RootDatabase) -> SyntaxTreeStats {
-    base_db::ParseQuery.in_db(db).entries::<SyntaxTreeStats>()
+    ide_db::base_db::ParseQuery.in_db(db).entries::<SyntaxTreeStats>()
 }
 fn macro_syntax_tree_stats(db: &RootDatabase) -> SyntaxTreeStats {
     hir::db::ParseMacroQuery.in_db(db).entries::<SyntaxTreeStats>()
diff --git a/crates/ide/src/syntax_highlighting.rs b/crates/ide/src/syntax_highlighting.rs
index b35c03162..9f864179e 100644
--- a/crates/ide/src/syntax_highlighting.rs
+++ b/crates/ide/src/syntax_highlighting.rs
@@ -579,7 +579,14 @@ fn highlight_element(
                 }
             }
             T![-] if element.parent().and_then(ast::PrefixExpr::cast).is_some() => {
-                HighlightTag::NumericLiteral.into()
+                let prefix_expr = element.parent().and_then(ast::PrefixExpr::cast)?;
+
+                let expr = prefix_expr.expr()?;
+                match expr {
+                    ast::Expr::Literal(_) => HighlightTag::NumericLiteral,
+                    _ => HighlightTag::Operator,
+                }
+                .into()
             }
             _ if element.parent().and_then(ast::PrefixExpr::cast).is_some() => {
                 HighlightTag::Operator.into()
@@ -763,6 +770,9 @@ fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
             if local.is_mut(db) || local.ty(db).is_mutable_reference() {
                 h |= HighlightModifier::Mutable;
             }
+            if local.ty(db).as_callable(db).is_some() || local.ty(db).impls_fnonce(db) {
+                h |= HighlightModifier::Callable;
+            }
             return h;
         }
     }
diff --git a/crates/ide/src/syntax_highlighting/html.rs b/crates/ide/src/syntax_highlighting/html.rs
index 57e2d2923..abcc5cccc 100644
--- a/crates/ide/src/syntax_highlighting/html.rs
+++ b/crates/ide/src/syntax_highlighting/html.rs
@@ -1,6 +1,6 @@
 //! Renders a bit of code as HTML.
 
-use base_db::SourceDatabase;
+use ide_db::base_db::SourceDatabase;
 use oorandom::Rand32;
 use stdx::format_to;
 use syntax::{AstNode, TextRange, TextSize};
diff --git a/crates/ide/src/syntax_highlighting/injection.rs b/crates/ide/src/syntax_highlighting/injection.rs
index acd91b26c..59a74bc02 100644
--- a/crates/ide/src/syntax_highlighting/injection.rs
+++ b/crates/ide/src/syntax_highlighting/injection.rs
@@ -3,8 +3,8 @@
 use std::{collections::BTreeMap, convert::TryFrom};
 
 use ast::{HasQuotes, HasStringValue};
-use call_info::ActiveParameter;
 use hir::Semantics;
+use ide_db::call_info::ActiveParameter;
 use itertools::Itertools;
 use syntax::{ast, AstToken, SyntaxNode, SyntaxToken, TextRange, TextSize};
 
diff --git a/crates/ide/src/syntax_highlighting/tags.rs b/crates/ide/src/syntax_highlighting/tags.rs
index c1b817f06..e8f78ad52 100644
--- a/crates/ide/src/syntax_highlighting/tags.rs
+++ b/crates/ide/src/syntax_highlighting/tags.rs
@@ -64,6 +64,7 @@ pub enum HighlightModifier {
     Mutable,
     Consuming,
     Unsafe,
+    Callable,
 }
 
 impl HighlightTag {
@@ -122,6 +123,7 @@ impl HighlightModifier {
         HighlightModifier::Mutable,
         HighlightModifier::Consuming,
         HighlightModifier::Unsafe,
+        HighlightModifier::Callable,
     ];
 
     fn as_str(self) -> &'static str {
@@ -134,6 +136,7 @@ impl HighlightModifier {
             HighlightModifier::Mutable => "mutable",
             HighlightModifier::Consuming => "consuming",
             HighlightModifier::Unsafe => "unsafe",
+            HighlightModifier::Callable => "callable",
         }
     }
 
diff --git a/crates/ide/src/syntax_highlighting/test_data/highlighting.html b/crates/ide/src/syntax_highlighting/test_data/highlighting.html
index 0bb0928e4..c6b4f5a00 100644
--- a/crates/ide/src/syntax_highlighting/test_data/highlighting.html
+++ b/crates/ide/src/syntax_highlighting/test_data/highlighting.html
@@ -44,6 +44,17 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="keyword">pub</span> <span class="keyword">trait</span> <span class="trait declaration">Copy</span> <span class="punctuation">{</span><span class="punctuation">}</span>
 <span class="punctuation">}</span>
 
+<span class="keyword">pub</span> <span class="keyword">mod</span> <span class="module declaration">ops</span> <span class="punctuation">{</span>
+    <span class="attribute">#</span><span class="attribute">[</span><span class="function attribute">lang</span><span class="attribute"> </span><span class="operator">=</span><span class="attribute"> </span><span class="string_literal">"fn_once"</span><span class="attribute">]</span>
+    <span class="keyword">pub</span> <span class="keyword">trait</span> <span class="trait declaration">FnOnce</span><span class="punctuation">&lt;</span><span class="type_param declaration">Args</span><span class="punctuation">&gt;</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+
+    <span class="attribute">#</span><span class="attribute">[</span><span class="function attribute">lang</span><span class="attribute"> </span><span class="operator">=</span><span class="attribute"> </span><span class="string_literal">"fn_mut"</span><span class="attribute">]</span>
+    <span class="keyword">pub</span> <span class="keyword">trait</span> <span class="trait declaration">FnMut</span><span class="punctuation">&lt;</span><span class="type_param declaration">Args</span><span class="punctuation">&gt;</span><span class="punctuation">:</span> <span class="trait">FnOnce</span><span class="punctuation">&lt;</span><span class="type_param">Args</span><span class="punctuation">&gt;</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+
+    <span class="attribute">#</span><span class="attribute">[</span><span class="function attribute">lang</span><span class="attribute"> </span><span class="operator">=</span><span class="attribute"> </span><span class="string_literal">"fn"</span><span class="attribute">]</span>
+    <span class="keyword">pub</span> <span class="keyword">trait</span> <span class="trait declaration">Fn</span><span class="punctuation">&lt;</span><span class="type_param declaration">Args</span><span class="punctuation">&gt;</span><span class="punctuation">:</span> <span class="trait">FnMut</span><span class="punctuation">&lt;</span><span class="type_param">Args</span><span class="punctuation">&gt;</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+<span class="punctuation">}</span>
+
 
 <span class="keyword">struct</span> <span class="struct declaration">Foo</span> <span class="punctuation">{</span>
     <span class="keyword">pub</span> <span class="field declaration">x</span><span class="punctuation">:</span> <span class="builtin_type">i32</span><span class="punctuation">,</span>
@@ -99,6 +110,11 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="function">foo</span><span class="operator">::</span><span class="punctuation">&lt;</span><span class="lifetime">'a</span><span class="punctuation">,</span> <span class="builtin_type">i32</span><span class="punctuation">&gt;</span><span class="punctuation">(</span><span class="punctuation">)</span>
 <span class="punctuation">}</span>
 
+<span class="keyword">use</span> <span class="module">ops</span><span class="operator">::</span><span class="trait">Fn</span><span class="punctuation">;</span>
+<span class="keyword">fn</span> <span class="function declaration">baz</span><span class="punctuation">&lt;</span><span class="type_param declaration">F</span><span class="punctuation">:</span> <span class="trait">Fn</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="operator">-&gt;</span> <span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">&gt;</span><span class="punctuation">(</span><span class="value_param declaration callable">f</span><span class="punctuation">:</span> <span class="type_param">F</span><span class="punctuation">)</span> <span class="punctuation">{</span>
+    <span class="value_param callable">f</span><span class="punctuation">(</span><span class="punctuation">)</span>
+<span class="punctuation">}</span>
+
 <span class="macro">macro_rules!</span> <span class="macro declaration">def_fn</span> <span class="punctuation">{</span>
     <span class="punctuation">(</span><span class="punctuation">$</span><span class="punctuation">(</span><span class="punctuation">$</span>tt<span class="punctuation">:</span>tt<span class="punctuation">)</span><span class="punctuation">*</span><span class="punctuation">)</span> <span class="operator">=</span><span class="punctuation">&gt;</span> <span class="punctuation">{</span><span class="punctuation">$</span><span class="punctuation">(</span><span class="punctuation">$</span>tt<span class="punctuation">)</span><span class="punctuation">*</span><span class="punctuation">}</span>
 <span class="punctuation">}</span>
@@ -157,6 +173,12 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="variable mutable">copy</span><span class="punctuation">.</span><span class="function">quop</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
     <span class="variable mutable">copy</span><span class="punctuation">.</span><span class="function mutable">qux</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
     <span class="variable mutable">copy</span><span class="punctuation">.</span><span class="function">baz</span><span class="punctuation">(</span><span class="variable mutable">copy</span><span class="punctuation">)</span><span class="punctuation">;</span>
+
+    <span class="keyword">let</span> <span class="variable declaration callable">a</span> <span class="operator">=</span> <span class="punctuation">|</span><span class="value_param declaration">x</span><span class="punctuation">|</span> <span class="value_param">x</span><span class="punctuation">;</span>
+    <span class="keyword">let</span> <span class="variable declaration callable">bar</span> <span class="operator">=</span> <span class="struct">Foo</span><span class="operator">::</span><span class="function">baz</span><span class="punctuation">;</span>
+
+    <span class="keyword">let</span> <span class="variable declaration">baz</span> <span class="operator">=</span> <span class="numeric_literal">-</span><span class="numeric_literal">42</span><span class="punctuation">;</span>
+    <span class="keyword">let</span> <span class="variable declaration">baz</span> <span class="operator">=</span> <span class="operator">-</span><span class="variable">baz</span><span class="punctuation">;</span>
 <span class="punctuation">}</span>
 
 <span class="keyword">enum</span> <span class="enum declaration">Option</span><span class="punctuation">&lt;</span><span class="type_param declaration">T</span><span class="punctuation">&gt;</span> <span class="punctuation">{</span>
diff --git a/crates/ide/src/syntax_highlighting/tests.rs b/crates/ide/src/syntax_highlighting/tests.rs
index 126363b8b..dd43f9dd9 100644
--- a/crates/ide/src/syntax_highlighting/tests.rs
+++ b/crates/ide/src/syntax_highlighting/tests.rs
@@ -18,6 +18,17 @@ pub mod marker {
     pub trait Copy {}
 }
 
+pub mod ops {
+    #[lang = "fn_once"]
+    pub trait FnOnce<Args> {}
+
+    #[lang = "fn_mut"]
+    pub trait FnMut<Args>: FnOnce<Args> {}
+
+    #[lang = "fn"]
+    pub trait Fn<Args>: FnMut<Args> {}
+}
+
 
 struct Foo {
     pub x: i32,
@@ -73,6 +84,11 @@ fn foo<'a, T>() -> T {
     foo::<'a, i32>()
 }
 
+use ops::Fn;
+fn baz<F: Fn() -> ()>(f: F) {
+    f()
+}
+
 macro_rules! def_fn {
     ($($tt:tt)*) => {$($tt)*}
 }
@@ -131,6 +147,12 @@ fn main() {
     copy.quop();
     copy.qux();
     copy.baz(copy);
+
+    let a = |x| x;
+    let bar = Foo::baz;
+
+    let baz = -42;
+    let baz = -baz;
 }
 
 enum Option<T> {
diff --git a/crates/ide/src/syntax_tree.rs b/crates/ide/src/syntax_tree.rs
index 0eed2dbd7..7941610d6 100644
--- a/crates/ide/src/syntax_tree.rs
+++ b/crates/ide/src/syntax_tree.rs
@@ -1,4 +1,4 @@
-use base_db::{FileId, SourceDatabase};
+use ide_db::base_db::{FileId, SourceDatabase};
 use ide_db::RootDatabase;
 use syntax::{
     algo, AstNode, NodeOrToken, SourceFile,
diff --git a/crates/ide/src/typing.rs b/crates/ide/src/typing.rs
index 94b91f049..43458a3a2 100644
--- a/crates/ide/src/typing.rs
+++ b/crates/ide/src/typing.rs
@@ -15,7 +15,7 @@
 
 mod on_enter;
 
-use base_db::{FilePosition, SourceDatabase};
+use ide_db::base_db::{FilePosition, SourceDatabase};
 use ide_db::{source_change::SourceFileEdit, RootDatabase};
 use syntax::{
     algo::find_node_at_offset,
diff --git a/crates/ide/src/typing/on_enter.rs b/crates/ide/src/typing/on_enter.rs
index 98adef1d6..f4ea30352 100644
--- a/crates/ide/src/typing/on_enter.rs
+++ b/crates/ide/src/typing/on_enter.rs
@@ -1,7 +1,7 @@
 //! Handles the `Enter` key press. At the momently, this only continues
 //! comments, but should handle indent some time in the future as well.
 
-use base_db::{FilePosition, SourceDatabase};
+use ide_db::base_db::{FilePosition, SourceDatabase};
 use ide_db::RootDatabase;
 use syntax::{
     ast::{self, AstToken},
diff --git a/crates/ide_db/Cargo.toml b/crates/ide_db/Cargo.toml
index 320fb15e5..72a9212f1 100644
--- a/crates/ide_db/Cargo.toml
+++ b/crates/ide_db/Cargo.toml
@@ -14,7 +14,7 @@ wasm = []
 
 [dependencies]
 log = "0.4.8"
-rayon = "1.3.0"
+rayon = "1.5.0"
 fst = { version = "0.4", default-features = false }
 rustc-hash = "1.1.0"
 once_cell = "1.3.1"
@@ -29,3 +29,6 @@ test_utils = { path = "../test_utils", version = "0.0.0" }
 # ide should depend only on the top-level `hir` package. if you need
 # something from some `hir_xxx` subpackage, reexport the API via `hir`.
 hir = { path = "../hir", version = "0.0.0" }
+
+[dev-dependencies]
+expect-test = "1.0"
diff --git a/crates/call_info/src/lib.rs b/crates/ide_db/src/call_info.rs
index c45406c25..83a602b9a 100644
--- a/crates/call_info/src/lib.rs
+++ b/crates/ide_db/src/call_info.rs
@@ -2,7 +2,6 @@
 use base_db::FilePosition;
 use either::Either;
 use hir::{HasAttrs, HirDisplay, Semantics, Type};
-use ide_db::RootDatabase;
 use stdx::format_to;
 use syntax::{
     ast::{self, ArgListOwner},
@@ -10,6 +9,8 @@ use syntax::{
 };
 use test_utils::mark;
 
+use crate::RootDatabase;
+
 /// Contains information about a call site. Specifically the
 /// `FunctionSignature`and current parameter.
 #[derive(Debug)]
@@ -228,9 +229,9 @@ impl FnCallNode {
 
 #[cfg(test)]
 mod tests {
+    use crate::RootDatabase;
     use base_db::{fixture::ChangeFixture, FilePosition};
     use expect_test::{expect, Expect};
-    use ide_db::RootDatabase;
     use test_utils::{mark, RangeOrOffset};
 
     /// Creates analysis from a multi-file fixture, returns positions marked with <|>.
@@ -249,7 +250,7 @@ mod tests {
 
     fn check(ra_fixture: &str, expect: Expect) {
         let (db, position) = position(ra_fixture);
-        let call_info = crate::call_info(&db, position);
+        let call_info = crate::call_info::call_info(&db, position);
         let actual = match call_info {
             Some(call_info) => {
                 let docs = match &call_info.doc {
diff --git a/crates/ide_db/src/lib.rs b/crates/ide_db/src/lib.rs
index 7eff247c7..38ebdbf79 100644
--- a/crates/ide_db/src/lib.rs
+++ b/crates/ide_db/src/lib.rs
@@ -10,6 +10,9 @@ pub mod defs;
 pub mod search;
 pub mod imports_locator;
 pub mod source_change;
+pub mod ty_filter;
+pub mod traits;
+pub mod call_info;
 
 use std::{fmt, sync::Arc};
 
@@ -23,6 +26,9 @@ use rustc_hash::FxHashSet;
 
 use crate::{line_index::LineIndex, symbol_index::SymbolsDatabase};
 
+/// `base_db` is normally also needed in places where `ide_db` is used, so this re-export is for convenience.
+pub use base_db;
+
 #[salsa::database(
     base_db::SourceDatabaseStorage,
     base_db::SourceDatabaseExtStorage,
diff --git a/crates/ide_db/src/traits.rs b/crates/ide_db/src/traits.rs
new file mode 100644
index 000000000..f57b6dd91
--- /dev/null
+++ b/crates/ide_db/src/traits.rs
@@ -0,0 +1,227 @@
+//! Functionality for obtaining data related to traits from the DB.
+
+use crate::RootDatabase;
+use hir::Semantics;
+use rustc_hash::FxHashSet;
+use syntax::{
+    ast::{self, NameOwner},
+    AstNode,
+};
+
+/// Given the `impl` block, attempts to find the trait this `impl` corresponds to.
+pub fn resolve_target_trait(
+    sema: &Semantics<RootDatabase>,
+    impl_def: &ast::Impl,
+) -> Option<hir::Trait> {
+    let ast_path =
+        impl_def.trait_().map(|it| it.syntax().clone()).and_then(ast::PathType::cast)?.path()?;
+
+    match sema.resolve_path(&ast_path) {
+        Some(hir::PathResolution::Def(hir::ModuleDef::Trait(def))) => Some(def),
+        _ => None,
+    }
+}
+
+/// Given the `impl` block, returns the list of associated items (e.g. functions or types) that are
+/// missing in this `impl` block.
+pub fn get_missing_assoc_items(
+    sema: &Semantics<RootDatabase>,
+    impl_def: &ast::Impl,
+) -> Vec<hir::AssocItem> {
+    // Names must be unique between constants and functions. However, type aliases
+    // may share the same name as a function or constant.
+    let mut impl_fns_consts = FxHashSet::default();
+    let mut impl_type = FxHashSet::default();
+
+    if let Some(item_list) = impl_def.assoc_item_list() {
+        for item in item_list.assoc_items() {
+            match item {
+                ast::AssocItem::Fn(f) => {
+                    if let Some(n) = f.name() {
+                        impl_fns_consts.insert(n.syntax().to_string());
+                    }
+                }
+
+                ast::AssocItem::TypeAlias(t) => {
+                    if let Some(n) = t.name() {
+                        impl_type.insert(n.syntax().to_string());
+                    }
+                }
+
+                ast::AssocItem::Const(c) => {
+                    if let Some(n) = c.name() {
+                        impl_fns_consts.insert(n.syntax().to_string());
+                    }
+                }
+                ast::AssocItem::MacroCall(_) => (),
+            }
+        }
+    }
+
+    resolve_target_trait(sema, impl_def).map_or(vec![], |target_trait| {
+        target_trait
+            .items(sema.db)
+            .iter()
+            .filter(|i| match i {
+                hir::AssocItem::Function(f) => {
+                    !impl_fns_consts.contains(&f.name(sema.db).to_string())
+                }
+                hir::AssocItem::TypeAlias(t) => !impl_type.contains(&t.name(sema.db).to_string()),
+                hir::AssocItem::Const(c) => c
+                    .name(sema.db)
+                    .map(|n| !impl_fns_consts.contains(&n.to_string()))
+                    .unwrap_or_default(),
+            })
+            .cloned()
+            .collect()
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::RootDatabase;
+    use base_db::{fixture::ChangeFixture, FilePosition};
+    use expect_test::{expect, Expect};
+    use hir::Semantics;
+    use syntax::ast::{self, AstNode};
+    use test_utils::RangeOrOffset;
+
+    /// Creates analysis from a multi-file fixture, returns positions marked with <|>.
+    pub(crate) fn position(ra_fixture: &str) -> (RootDatabase, FilePosition) {
+        let change_fixture = ChangeFixture::parse(ra_fixture);
+        let mut database = RootDatabase::default();
+        database.apply_change(change_fixture.change);
+        let (file_id, range_or_offset) =
+            change_fixture.file_position.expect("expected a marker (<|>)");
+        let offset = match range_or_offset {
+            RangeOrOffset::Range(_) => panic!(),
+            RangeOrOffset::Offset(it) => it,
+        };
+        (database, FilePosition { file_id, offset })
+    }
+
+    fn check_trait(ra_fixture: &str, expect: Expect) {
+        let (db, position) = position(ra_fixture);
+        let sema = Semantics::new(&db);
+        let file = sema.parse(position.file_id);
+        let impl_block: ast::Impl =
+            sema.find_node_at_offset_with_descend(file.syntax(), position.offset).unwrap();
+        let trait_ = crate::traits::resolve_target_trait(&sema, &impl_block);
+        let actual = match trait_ {
+            Some(trait_) => trait_.name(&db).to_string(),
+            None => String::new(),
+        };
+        expect.assert_eq(&actual);
+    }
+
+    fn check_missing_assoc(ra_fixture: &str, expect: Expect) {
+        let (db, position) = position(ra_fixture);
+        let sema = Semantics::new(&db);
+        let file = sema.parse(position.file_id);
+        let impl_block: ast::Impl =
+            sema.find_node_at_offset_with_descend(file.syntax(), position.offset).unwrap();
+        let items = crate::traits::get_missing_assoc_items(&sema, &impl_block);
+        let actual = items
+            .into_iter()
+            .map(|item| item.name(&db).unwrap().to_string())
+            .collect::<Vec<_>>()
+            .join("\n");
+        expect.assert_eq(&actual);
+    }
+
+    #[test]
+    fn resolve_trait() {
+        check_trait(
+            r#"
+pub trait Foo {
+    fn bar();
+}
+impl Foo for u8 {
+    <|>
+}
+            "#,
+            expect![["Foo"]],
+        );
+        check_trait(
+            r#"
+pub trait Foo {
+    fn bar();
+}
+impl Foo for u8 {
+    fn bar() {
+        fn baz() {
+            <|>
+        }
+        baz();
+    }
+}
+            "#,
+            expect![["Foo"]],
+        );
+        check_trait(
+            r#"
+pub trait Foo {
+    fn bar();
+}
+pub struct Bar;
+impl Bar {
+    <|>
+}
+            "#,
+            expect![[""]],
+        );
+    }
+
+    #[test]
+    fn missing_assoc_items() {
+        check_missing_assoc(
+            r#"
+pub trait Foo {
+    const FOO: u8;
+    fn bar();
+}
+impl Foo for u8 {
+    <|>
+}"#,
+            expect![[r#"
+                FOO
+                bar"#]],
+        );
+
+        check_missing_assoc(
+            r#"
+pub trait Foo {
+    const FOO: u8;
+    fn bar();
+}
+impl Foo for u8 {
+    const FOO: u8 = 10;
+    <|>
+}"#,
+            expect![[r#"
+                bar"#]],
+        );
+
+        check_missing_assoc(
+            r#"
+pub trait Foo {
+    const FOO: u8;
+    fn bar();
+}
+impl Foo for u8 {
+    const FOO: u8 = 10;
+    fn bar() {<|>}
+}"#,
+            expect![[r#""#]],
+        );
+
+        check_missing_assoc(
+            r#"
+pub struct Foo;
+impl Foo {
+    fn bar() {<|>}
+}"#,
+            expect![[r#""#]],
+        );
+    }
+}
diff --git a/crates/ide_db/src/ty_filter.rs b/crates/ide_db/src/ty_filter.rs
new file mode 100644
index 000000000..63a945282
--- /dev/null
+++ b/crates/ide_db/src/ty_filter.rs
@@ -0,0 +1,58 @@
+//! This module contains structures for filtering the expected types.
+//! Use case for structures in this module is, for example, situation when you need to process
+//! only certain `Enum`s.
+
+use crate::RootDatabase;
+use hir::{Adt, Semantics, Type};
+use std::iter;
+use syntax::ast::{self, make};
+
+/// Enum types that implement `std::ops::Try` trait.
+#[derive(Clone, Copy)]
+pub enum TryEnum {
+    Result,
+    Option,
+}
+
+impl TryEnum {
+    const ALL: [TryEnum; 2] = [TryEnum::Option, TryEnum::Result];
+
+    /// Returns `Some(..)` if the provided type is an enum that implements `std::ops::Try`.
+    pub fn from_ty(sema: &Semantics<RootDatabase>, ty: &Type) -> Option<TryEnum> {
+        let enum_ = match ty.as_adt() {
+            Some(Adt::Enum(it)) => it,
+            _ => return None,
+        };
+        TryEnum::ALL.iter().find_map(|&var| {
+            if &enum_.name(sema.db).to_string() == var.type_name() {
+                return Some(var);
+            }
+            None
+        })
+    }
+
+    pub fn happy_case(self) -> &'static str {
+        match self {
+            TryEnum::Result => "Ok",
+            TryEnum::Option => "Some",
+        }
+    }
+
+    pub fn sad_pattern(self) -> ast::Pat {
+        match self {
+            TryEnum::Result => make::tuple_struct_pat(
+                make::path_unqualified(make::path_segment(make::name_ref("Err"))),
+                iter::once(make::wildcard_pat().into()),
+            )
+            .into(),
+            TryEnum::Option => make::ident_pat(make::name("None")).into(),
+        }
+    }
+
+    fn type_name(self) -> &'static str {
+        match self {
+            TryEnum::Result => "Result",
+            TryEnum::Option => "Option",
+        }
+    }
+}
diff --git a/crates/rust-analyzer/Cargo.toml b/crates/rust-analyzer/Cargo.toml
index 66cf06e1a..975b24aaf 100644
--- a/crates/rust-analyzer/Cargo.toml
+++ b/crates/rust-analyzer/Cargo.toml
@@ -29,9 +29,12 @@ rustc-hash = "1.1.0"
 serde = { version = "1.0.106", features = ["derive"] }
 serde_json = "1.0.48"
 threadpool = "1.7.1"
-rayon = "1.3.1"
+rayon = "1.5"
 mimalloc = { version = "0.1.19", default-features = false, optional = true }
 lsp-server = "0.4.0"
+tracing = "0.1"
+tracing-subscriber = { version = "0.2", default-features = false, features = ["env-filter", "registry"] }
+tracing-tree = { version = "0.1.4" }
 
 stdx = { path = "../stdx", version = "0.0.0" }
 flycheck = { path = "../flycheck", version = "0.0.0" }
@@ -46,7 +49,6 @@ cfg = { path = "../cfg", version = "0.0.0" }
 toolchain = { path = "../toolchain", version = "0.0.0" }
 
 # This should only be used in CLI
-base_db = { path = "../base_db", version = "0.0.0" }
 ide_db = { path = "../ide_db", version = "0.0.0" }
 ssr = { path = "../ssr", version = "0.0.0" }
 hir = { path = "../hir", version = "0.0.0" }
diff --git a/crates/rust-analyzer/src/bin/main.rs b/crates/rust-analyzer/src/bin/main.rs
index 97b246a32..4175e569e 100644
--- a/crates/rust-analyzer/src/bin/main.rs
+++ b/crates/rust-analyzer/src/bin/main.rs
@@ -68,10 +68,32 @@ fn setup_logging(log_file: Option<PathBuf>) -> Result<()> {
     let filter = env::var("RA_LOG").ok();
     logger::Logger::new(log_file, filter.as_deref()).install();
 
+    tracing_setup::setup_tracing()?;
+
     profile::init();
     Ok(())
 }
 
+mod tracing_setup {
+    use tracing::subscriber;
+    use tracing_subscriber::layer::SubscriberExt;
+    use tracing_subscriber::EnvFilter;
+    use tracing_subscriber::Registry;
+    use tracing_tree::HierarchicalLayer;
+
+    pub fn setup_tracing() -> super::Result<()> {
+        let filter = EnvFilter::from_env("CHALK_DEBUG");
+        let layer = HierarchicalLayer::default()
+            .with_indent_lines(true)
+            .with_ansi(false)
+            .with_indent_amount(2)
+            .with_writer(std::io::stderr);
+        let subscriber = Registry::default().with(filter).with(layer);
+        subscriber::set_global_default(subscriber)?;
+        Ok(())
+    }
+}
+
 fn run_server() -> Result<()> {
     log::info!("server will start");
 
diff --git a/crates/rust-analyzer/src/cargo_target_spec.rs b/crates/rust-analyzer/src/cargo_target_spec.rs
index ddc028148..1ab72bd91 100644
--- a/crates/rust-analyzer/src/cargo_target_spec.rs
+++ b/crates/rust-analyzer/src/cargo_target_spec.rs
@@ -1,6 +1,6 @@
 //! See `CargoTargetSpec`
 
-use cfg::CfgExpr;
+use cfg::{CfgAtom, CfgExpr};
 use ide::{FileId, RunnableKind, TestId};
 use project_model::{self, TargetKind};
 use vfs::AbsPathBuf;
@@ -24,7 +24,7 @@ impl CargoTargetSpec {
         snap: &GlobalStateSnapshot,
         spec: Option<CargoTargetSpec>,
         kind: &RunnableKind,
-        cfgs: &[CfgExpr],
+        cfg: &Option<CfgExpr>,
     ) -> Result<(Vec<String>, Vec<String>)> {
         let mut args = Vec::new();
         let mut extra_args = Vec::new();
@@ -87,7 +87,7 @@ impl CargoTargetSpec {
             args.push("--all-features".to_string());
         } else {
             let mut features = Vec::new();
-            for cfg in cfgs {
+            if let Some(cfg) = cfg.as_ref() {
                 required_features(cfg, &mut features);
             }
             for feature in &snap.config.cargo.features {
@@ -160,7 +160,9 @@ impl CargoTargetSpec {
 /// Fill minimal features needed
 fn required_features(cfg_expr: &CfgExpr, features: &mut Vec<String>) {
     match cfg_expr {
-        CfgExpr::KeyValue { key, value } if key == "feature" => features.push(value.to_string()),
+        CfgExpr::Atom(CfgAtom::KeyValue { key, value }) if key == "feature" => {
+            features.push(value.to_string())
+        }
         CfgExpr::All(preds) => {
             preds.iter().for_each(|cfg| required_features(cfg, features));
         }
diff --git a/crates/rust-analyzer/src/cli/analysis_bench.rs b/crates/rust-analyzer/src/cli/analysis_bench.rs
index d1c095ba5..8e33986d5 100644
--- a/crates/rust-analyzer/src/cli/analysis_bench.rs
+++ b/crates/rust-analyzer/src/cli/analysis_bench.rs
@@ -3,13 +3,13 @@
 use std::{env, path::PathBuf, str::FromStr, sync::Arc, time::Instant};
 
 use anyhow::{bail, format_err, Result};
-use base_db::{
-    salsa::{Database, Durability},
-    FileId,
-};
 use ide::{
     Analysis, AnalysisHost, Change, CompletionConfig, DiagnosticsConfig, FilePosition, LineCol,
 };
+use ide_db::base_db::{
+    salsa::{Database, Durability},
+    FileId,
+};
 use vfs::AbsPathBuf;
 
 use crate::{
diff --git a/crates/rust-analyzer/src/cli/analysis_stats.rs b/crates/rust-analyzer/src/cli/analysis_stats.rs
index fb2b2b000..98ef0cd68 100644
--- a/crates/rust-analyzer/src/cli/analysis_stats.rs
+++ b/crates/rust-analyzer/src/cli/analysis_stats.rs
@@ -6,16 +6,16 @@ use std::{
     time::{SystemTime, UNIX_EPOCH},
 };
 
-use base_db::{
-    salsa::{self, ParallelDatabase},
-    SourceDatabaseExt,
-};
 use hir::{
     db::{AstDatabase, DefDatabase, HirDatabase},
     original_range, AssocItem, Crate, HasSource, HirDisplay, ModuleDef,
 };
 use hir_def::FunctionId;
 use hir_ty::{Ty, TypeWalk};
+use ide_db::base_db::{
+    salsa::{self, ParallelDatabase},
+    SourceDatabaseExt,
+};
 use itertools::Itertools;
 use oorandom::Rand32;
 use rayon::prelude::*;
diff --git a/crates/rust-analyzer/src/cli/diagnostics.rs b/crates/rust-analyzer/src/cli/diagnostics.rs
index a89993a2b..368f627ac 100644
--- a/crates/rust-analyzer/src/cli/diagnostics.rs
+++ b/crates/rust-analyzer/src/cli/diagnostics.rs
@@ -6,9 +6,9 @@ use std::path::Path;
 use anyhow::anyhow;
 use rustc_hash::FxHashSet;
 
-use base_db::SourceDatabaseExt;
 use hir::Crate;
 use ide::{DiagnosticsConfig, Severity};
+use ide_db::base_db::SourceDatabaseExt;
 
 use crate::cli::{load_cargo::load_cargo, Result};
 
diff --git a/crates/rust-analyzer/src/cli/load_cargo.rs b/crates/rust-analyzer/src/cli/load_cargo.rs
index 7ae1c9055..ab1e2ab92 100644
--- a/crates/rust-analyzer/src/cli/load_cargo.rs
+++ b/crates/rust-analyzer/src/cli/load_cargo.rs
@@ -3,9 +3,9 @@
 use std::{path::Path, sync::Arc};
 
 use anyhow::Result;
-use base_db::CrateGraph;
 use crossbeam_channel::{unbounded, Receiver};
 use ide::{AnalysisHost, Change};
+use ide_db::base_db::CrateGraph;
 use project_model::{CargoConfig, ProcMacroClient, ProjectManifest, ProjectWorkspace};
 use vfs::{loader::Handle, AbsPath, AbsPathBuf};
 
diff --git a/crates/rust-analyzer/src/cli/ssr.rs b/crates/rust-analyzer/src/cli/ssr.rs
index c11e10943..a06631dac 100644
--- a/crates/rust-analyzer/src/cli/ssr.rs
+++ b/crates/rust-analyzer/src/cli/ssr.rs
@@ -4,7 +4,7 @@ use crate::cli::{load_cargo::load_cargo, Result};
 use ssr::{MatchFinder, SsrPattern, SsrRule};
 
 pub fn apply_ssr_rules(rules: Vec<SsrRule>) -> Result<()> {
-    use base_db::SourceDatabaseExt;
+    use ide_db::base_db::SourceDatabaseExt;
     let (host, vfs) = load_cargo(&std::env::current_dir()?, true, true)?;
     let db = host.raw_database();
     let mut match_finder = MatchFinder::at_first_file(db)?;
@@ -26,7 +26,7 @@ pub fn apply_ssr_rules(rules: Vec<SsrRule>) -> Result<()> {
 /// `debug_snippet`. This is intended for debugging and probably isn't in it's current form useful
 /// for much else.
 pub fn search_for_patterns(patterns: Vec<SsrPattern>, debug_snippet: Option<String>) -> Result<()> {
-    use base_db::SourceDatabaseExt;
+    use ide_db::base_db::SourceDatabaseExt;
     use ide_db::symbol_index::SymbolsDatabase;
     let (host, _vfs) = load_cargo(&std::env::current_dir()?, true, true)?;
     let db = host.raw_database();
diff --git a/crates/rust-analyzer/src/dispatch.rs b/crates/rust-analyzer/src/dispatch.rs
index 9c8815e29..7a87515e9 100644
--- a/crates/rust-analyzer/src/dispatch.rs
+++ b/crates/rust-analyzer/src/dispatch.rs
@@ -34,7 +34,7 @@ impl<'a> RequestDispatcher<'a> {
         };
         let world = panic::AssertUnwindSafe(&mut *self.global_state);
         let response = panic::catch_unwind(move || {
-            stdx::panic_context::enter(format!("request: {} {:#?}", R::METHOD, params));
+            let _pctx = stdx::panic_context::enter(format!("request: {} {:#?}", R::METHOD, params));
             let result = f(world.0, params);
             result_to_response::<R>(id, result)
         })
@@ -64,7 +64,7 @@ impl<'a> RequestDispatcher<'a> {
             let world = self.global_state.snapshot();
 
             move || {
-                let _ctx =
+                let _pctx =
                     stdx::panic_context::enter(format!("request: {} {:#?}", R::METHOD, params));
                 let result = f(world, params);
                 Task::Response(result_to_response::<R>(id, result))
@@ -160,7 +160,7 @@ impl<'a> NotificationDispatcher<'a> {
                 return Ok(self);
             }
         };
-        stdx::panic_context::enter(format!("notification: {}", N::METHOD));
+        let _pctx = stdx::panic_context::enter(format!("notification: {}", N::METHOD));
         f(self.global_state, params)?;
         Ok(self)
     }
diff --git a/crates/rust-analyzer/src/from_proto.rs b/crates/rust-analyzer/src/from_proto.rs
index 5b9f52993..aa6b808d6 100644
--- a/crates/rust-analyzer/src/from_proto.rs
+++ b/crates/rust-analyzer/src/from_proto.rs
@@ -1,8 +1,8 @@
 //! Conversion lsp_types types to rust-analyzer specific ones.
 use std::convert::TryFrom;
 
-use base_db::{FileId, FilePosition, FileRange};
 use ide::{AssistKind, LineCol, LineIndex};
+use ide_db::base_db::{FileId, FilePosition, FileRange};
 use syntax::{TextRange, TextSize};
 use vfs::AbsPathBuf;
 
diff --git a/crates/rust-analyzer/src/global_state.rs b/crates/rust-analyzer/src/global_state.rs
index dafab6a6a..673a2eebc 100644
--- a/crates/rust-analyzer/src/global_state.rs
+++ b/crates/rust-analyzer/src/global_state.rs
@@ -5,10 +5,10 @@
 
 use std::{sync::Arc, time::Instant};
 
-use base_db::{CrateId, VfsPath};
 use crossbeam_channel::{unbounded, Receiver, Sender};
 use flycheck::FlycheckHandle;
 use ide::{Analysis, AnalysisHost, Change, FileId};
+use ide_db::base_db::{CrateId, VfsPath};
 use lsp_types::{SemanticTokens, Url};
 use parking_lot::{Mutex, RwLock};
 use project_model::{CargoWorkspace, ProcMacroClient, ProjectWorkspace, Target};
diff --git a/crates/rust-analyzer/src/lsp_utils.rs b/crates/rust-analyzer/src/lsp_utils.rs
index bd888f634..1d271a9d8 100644
--- a/crates/rust-analyzer/src/lsp_utils.rs
+++ b/crates/rust-analyzer/src/lsp_utils.rs
@@ -1,8 +1,8 @@
 //! Utilities for LSP-related boilerplate code.
 use std::{error::Error, ops::Range};
 
-use base_db::Canceled;
 use ide::LineIndex;
+use ide_db::base_db::Canceled;
 use lsp_server::Notification;
 
 use crate::{from_proto, global_state::GlobalState};
diff --git a/crates/rust-analyzer/src/main_loop.rs b/crates/rust-analyzer/src/main_loop.rs
index fb18f9014..ed5292733 100644
--- a/crates/rust-analyzer/src/main_loop.rs
+++ b/crates/rust-analyzer/src/main_loop.rs
@@ -5,10 +5,10 @@ use std::{
     time::{Duration, Instant},
 };
 
-use base_db::VfsPath;
 use crossbeam_channel::{select, Receiver};
 use ide::PrimeCachesProgress;
 use ide::{Canceled, FileId};
+use ide_db::base_db::VfsPath;
 use lsp_server::{Connection, Notification, Request, Response};
 use lsp_types::notification::Notification as _;
 use project_model::ProjectWorkspace;
diff --git a/crates/rust-analyzer/src/reload.rs b/crates/rust-analyzer/src/reload.rs
index f7215f129..0eabd51bd 100644
--- a/crates/rust-analyzer/src/reload.rs
+++ b/crates/rust-analyzer/src/reload.rs
@@ -1,9 +1,9 @@
 //! Project loading & configuration updates
 use std::{mem, sync::Arc};
 
-use base_db::{CrateGraph, SourceRoot, VfsPath};
 use flycheck::{FlycheckConfig, FlycheckHandle};
 use ide::Change;
+use ide_db::base_db::{CrateGraph, SourceRoot, VfsPath};
 use project_model::{ProcMacroClient, ProjectWorkspace};
 use vfs::{file_set::FileSetConfig, AbsPath, AbsPathBuf, ChangeKind};
 
diff --git a/crates/rust-analyzer/src/semantic_tokens.rs b/crates/rust-analyzer/src/semantic_tokens.rs
index a6c4d6099..7df28c9dd 100644
--- a/crates/rust-analyzer/src/semantic_tokens.rs
+++ b/crates/rust-analyzer/src/semantic_tokens.rs
@@ -77,6 +77,7 @@ define_semantic_token_modifiers![
     (CONSUMING, "consuming"),
     (UNSAFE, "unsafe"),
     (ATTRIBUTE_MODIFIER, "attribute"),
+    (CALLABLE, "callable"),
 ];
 
 #[derive(Default)]
diff --git a/crates/rust-analyzer/src/to_proto.rs b/crates/rust-analyzer/src/to_proto.rs
index 24ad49206..24a658fc6 100644
--- a/crates/rust-analyzer/src/to_proto.rs
+++ b/crates/rust-analyzer/src/to_proto.rs
@@ -4,13 +4,13 @@ use std::{
     sync::atomic::{AtomicU32, Ordering},
 };
 
-use base_db::{FileId, FileRange};
 use ide::{
     Assist, AssistKind, CallInfo, CompletionItem, CompletionItemKind, Documentation,
     FileSystemEdit, Fold, FoldKind, Highlight, HighlightModifier, HighlightTag, HighlightedRange,
     Indel, InlayHint, InlayKind, InsertTextFormat, LineIndex, Markup, NavigationTarget,
     ReferenceAccess, ResolvedAssist, Runnable, Severity, SourceChange, SourceFileEdit, TextEdit,
 };
+use ide_db::base_db::{FileId, FileRange};
 use itertools::Itertools;
 use syntax::{SyntaxKind, TextRange, TextSize};
 
@@ -425,6 +425,7 @@ fn semantic_token_type_and_modifiers(
             HighlightModifier::Mutable => semantic_tokens::MUTABLE,
             HighlightModifier::Consuming => semantic_tokens::CONSUMING,
             HighlightModifier::Unsafe => semantic_tokens::UNSAFE,
+            HighlightModifier::Callable => semantic_tokens::CALLABLE,
         };
         mods |= modifier;
     }
@@ -762,7 +763,7 @@ pub(crate) fn runnable(
     let workspace_root = spec.as_ref().map(|it| it.workspace_root.clone());
     let target = spec.as_ref().map(|s| s.target.clone());
     let (cargo_args, executable_args) =
-        CargoTargetSpec::runnable_args(snap, spec, &runnable.kind, &runnable.cfg_exprs)?;
+        CargoTargetSpec::runnable_args(snap, spec, &runnable.kind, &runnable.cfg)?;
     let label = runnable.label(target);
     let location = location_link(snap, None, runnable.nav)?;
 
@@ -808,7 +809,7 @@ mod tests {
         let completions: Vec<(String, Option<String>)> = analysis
             .completions(
                 &ide::CompletionConfig::default(),
-                base_db::FilePosition { file_id, offset },
+                ide_db::base_db::FilePosition { file_id, offset },
             )
             .unwrap()
             .unwrap()
diff --git a/crates/ssr/Cargo.toml b/crates/ssr/Cargo.toml
index 408140014..98ed25fb6 100644
--- a/crates/ssr/Cargo.toml
+++ b/crates/ssr/Cargo.toml
@@ -16,7 +16,6 @@ itertools = "0.9.0"
 
 text_edit = { path = "../text_edit", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
-base_db = { path = "../base_db", version = "0.0.0" }
 ide_db = { path = "../ide_db", version = "0.0.0" }
 hir = { path = "../hir", version = "0.0.0" }
 test_utils = { path = "../test_utils", version = "0.0.0" }
diff --git a/crates/ssr/src/lib.rs b/crates/ssr/src/lib.rs
index ba669fd56..747ce495d 100644
--- a/crates/ssr/src/lib.rs
+++ b/crates/ssr/src/lib.rs
@@ -73,8 +73,8 @@ use crate::errors::bail;
 pub use crate::errors::SsrError;
 pub use crate::matching::Match;
 use crate::matching::MatchFailureReason;
-use base_db::{FileId, FilePosition, FileRange};
 use hir::Semantics;
+use ide_db::base_db::{FileId, FilePosition, FileRange};
 use ide_db::source_change::SourceFileEdit;
 use resolving::ResolvedRule;
 use rustc_hash::FxHashMap;
@@ -126,7 +126,7 @@ impl<'db> MatchFinder<'db> {
 
     /// Constructs an instance using the start of the first file in `db` as the lookup context.
     pub fn at_first_file(db: &'db ide_db::RootDatabase) -> Result<MatchFinder<'db>, SsrError> {
-        use base_db::SourceDatabaseExt;
+        use ide_db::base_db::SourceDatabaseExt;
         use ide_db::symbol_index::SymbolsDatabase;
         if let Some(first_file_id) = db
             .local_roots()
@@ -160,7 +160,7 @@ impl<'db> MatchFinder<'db> {
 
     /// Finds matches for all added rules and returns edits for all found matches.
     pub fn edits(&self) -> Vec<SourceFileEdit> {
-        use base_db::SourceDatabaseExt;
+        use ide_db::base_db::SourceDatabaseExt;
         let mut matches_by_file = FxHashMap::default();
         for m in self.matches().matches {
             matches_by_file
@@ -205,7 +205,7 @@ impl<'db> MatchFinder<'db> {
     /// them, while recording reasons why they don't match. This API is useful for command
     /// line-based debugging where providing a range is difficult.
     pub fn debug_where_text_equal(&self, file_id: FileId, snippet: &str) -> Vec<MatchDebugInfo> {
-        use base_db::SourceDatabaseExt;
+        use ide_db::base_db::SourceDatabaseExt;
         let file = self.sema.parse(file_id);
         let mut res = Vec::new();
         let file_text = self.sema.db.file_text(file_id);
diff --git a/crates/ssr/src/matching.rs b/crates/ssr/src/matching.rs
index 948862a77..99b187311 100644
--- a/crates/ssr/src/matching.rs
+++ b/crates/ssr/src/matching.rs
@@ -6,8 +6,8 @@ use crate::{
     resolving::{ResolvedPattern, ResolvedRule, UfcsCallInfo},
     SsrMatches,
 };
-use base_db::FileRange;
 use hir::Semantics;
+use ide_db::base_db::FileRange;
 use rustc_hash::FxHashMap;
 use std::{cell::Cell, iter::Peekable};
 use syntax::ast::{AstNode, AstToken};
diff --git a/crates/ssr/src/resolving.rs b/crates/ssr/src/resolving.rs
index 347cc4aad..f5ceb5729 100644
--- a/crates/ssr/src/resolving.rs
+++ b/crates/ssr/src/resolving.rs
@@ -2,7 +2,7 @@
 
 use crate::errors::error;
 use crate::{parsing, SsrError};
-use base_db::FilePosition;
+use ide_db::base_db::FilePosition;
 use parsing::Placeholder;
 use rustc_hash::FxHashMap;
 use syntax::{ast, SmolStr, SyntaxKind, SyntaxNode, SyntaxToken};
diff --git a/crates/ssr/src/search.rs b/crates/ssr/src/search.rs
index a595fd269..44b5db029 100644
--- a/crates/ssr/src/search.rs
+++ b/crates/ssr/src/search.rs
@@ -5,7 +5,7 @@ use crate::{
     resolving::{ResolvedPath, ResolvedPattern, ResolvedRule},
     Match, MatchFinder,
 };
-use base_db::{FileId, FileRange};
+use ide_db::base_db::{FileId, FileRange};
 use ide_db::{
     defs::Definition,
     search::{Reference, SearchScope},
@@ -145,7 +145,7 @@ impl<'db> MatchFinder<'db> {
     fn search_files_do(&self, mut callback: impl FnMut(FileId)) {
         if self.restrict_ranges.is_empty() {
             // Unrestricted search.
-            use base_db::SourceDatabaseExt;
+            use ide_db::base_db::SourceDatabaseExt;
             use ide_db::symbol_index::SymbolsDatabase;
             for &root in self.sema.db.local_roots().iter() {
                 let sr = self.sema.db.source_root(root);
diff --git a/crates/ssr/src/tests.rs b/crates/ssr/src/tests.rs
index 20231a9bc..63131f6ca 100644
--- a/crates/ssr/src/tests.rs
+++ b/crates/ssr/src/tests.rs
@@ -1,6 +1,6 @@
 use crate::{MatchFinder, SsrRule};
-use base_db::{salsa::Durability, FileId, FilePosition, FileRange, SourceDatabaseExt};
 use expect_test::{expect, Expect};
+use ide_db::base_db::{salsa::Durability, FileId, FilePosition, FileRange, SourceDatabaseExt};
 use rustc_hash::FxHashSet;
 use std::sync::Arc;
 use test_utils::{mark, RangeOrOffset};
@@ -62,7 +62,7 @@ fn parser_undefined_placeholder_in_replacement() {
 /// `code` may optionally contain a cursor marker `<|>`. If it doesn't, then the position will be
 /// the start of the file. If there's a second cursor marker, then we'll return a single range.
 pub(crate) fn single_file(code: &str) -> (ide_db::RootDatabase, FilePosition, Vec<FileRange>) {
-    use base_db::fixture::WithFixture;
+    use ide_db::base_db::fixture::WithFixture;
     use ide_db::symbol_index::SymbolsDatabase;
     let (mut db, file_id, range_or_offset) = if code.contains(test_utils::CURSOR_MARKER) {
         ide_db::RootDatabase::with_range_or_offset(code)
@@ -83,7 +83,7 @@ pub(crate) fn single_file(code: &str) -> (ide_db::RootDatabase, FilePosition, Ve
         }
     }
     let mut local_roots = FxHashSet::default();
-    local_roots.insert(base_db::fixture::WORKSPACE);
+    local_roots.insert(ide_db::base_db::fixture::WORKSPACE);
     db.set_local_roots_with_durability(Arc::new(local_roots), Durability::HIGH);
     (db, position, selections)
 }
diff --git a/crates/stdx/src/panic_context.rs b/crates/stdx/src/panic_context.rs
index fd232e0cc..8d51e20d3 100644
--- a/crates/stdx/src/panic_context.rs
+++ b/crates/stdx/src/panic_context.rs
@@ -4,7 +4,7 @@
 
 use std::{cell::RefCell, panic, sync::Once};
 
-pub fn enter(context: String) -> impl Drop {
+pub fn enter(context: String) -> PanicContext {
     static ONCE: Once = Once::new();
     ONCE.call_once(PanicContext::init);
 
@@ -13,7 +13,7 @@ pub fn enter(context: String) -> impl Drop {
 }
 
 #[must_use]
-struct PanicContext {
+pub struct PanicContext {
     _priv: (),
 }
 
diff --git a/crates/syntax/Cargo.toml b/crates/syntax/Cargo.toml
index c343f2f70..e8de61868 100644
--- a/crates/syntax/Cargo.toml
+++ b/crates/syntax/Cargo.toml
@@ -13,10 +13,11 @@ doctest = false
 [dependencies]
 itertools = "0.9.0"
 rowan = "0.10.0"
-rustc_lexer = { version = "683.0.0", package = "rustc-ap-rustc_lexer" }
+rustc_lexer = { version = "685.0.0", package = "rustc-ap-rustc_lexer" }
 rustc-hash = "1.1.0"
 arrayvec = "0.5.1"
 once_cell = "1.3.1"
+indexmap = "1.4.0"
 # This crate transitively depends on `smol_str` via `rowan`.
 # ideally, `serde` should be enabled by `rust-analyzer`, but we enable it here
 # to reduce number of compilations
@@ -26,10 +27,9 @@ serde = { version = "1.0.106", features = ["derive"] }
 stdx = { path = "../stdx", version = "0.0.0" }
 text_edit = { path = "../text_edit", version = "0.0.0" }
 parser = { path = "../parser", version = "0.0.0" }
+test_utils = { path = "../test_utils" }
 
 [dev-dependencies]
 walkdir = "2.3.1"
 rayon = "1"
 expect-test = "1.0"
-
-test_utils = { path = "../test_utils" }
diff --git a/crates/syntax/src/algo.rs b/crates/syntax/src/algo.rs
index ea199f9b8..065035fe6 100644
--- a/crates/syntax/src/algo.rs
+++ b/crates/syntax/src/algo.rs
@@ -2,11 +2,14 @@
 
 use std::{
     fmt,
+    hash::BuildHasherDefault,
     ops::{self, RangeInclusive},
 };
 
+use indexmap::IndexMap;
 use itertools::Itertools;
 use rustc_hash::FxHashMap;
+use test_utils::mark;
 use text_edit::TextEditBuilder;
 
 use crate::{
@@ -106,42 +109,56 @@ pub enum InsertPosition<T> {
     After(T),
 }
 
+type FxIndexMap<K, V> = IndexMap<K, V, BuildHasherDefault<rustc_hash::FxHasher>>;
+
+#[derive(Debug)]
 pub struct TreeDiff {
     replacements: FxHashMap<SyntaxElement, SyntaxElement>,
+    deletions: Vec<SyntaxElement>,
+    // the vec as well as the indexmap are both here to preserve order
+    insertions: FxIndexMap<SyntaxElement, Vec<SyntaxElement>>,
 }
 
 impl TreeDiff {
     pub fn into_text_edit(&self, builder: &mut TextEditBuilder) {
+        for (anchor, to) in self.insertions.iter() {
+            to.iter().for_each(|to| builder.insert(anchor.text_range().end(), to.to_string()));
+        }
         for (from, to) in self.replacements.iter() {
             builder.replace(from.text_range(), to.to_string())
         }
+        for text_range in self.deletions.iter().map(SyntaxElement::text_range) {
+            builder.delete(text_range);
+        }
     }
 
     pub fn is_empty(&self) -> bool {
-        self.replacements.is_empty()
+        self.replacements.is_empty() && self.deletions.is_empty() && self.insertions.is_empty()
     }
 }
 
 /// Finds minimal the diff, which, applied to `from`, will result in `to`.
 ///
-/// Specifically, returns a map whose keys are descendants of `from` and values
-/// are descendants of `to`, such that  `replace_descendants(from, map) == to`.
+/// Specifically, returns a structure that consists of a replacements, insertions and deletions
+/// such that applying this map on `from` will result in `to`.
 ///
-/// A trivial solution is a singleton map `{ from: to }`, but this function
-/// tries to find a more fine-grained diff.
+/// This function tries to find a fine-grained diff.
 pub fn diff(from: &SyntaxNode, to: &SyntaxNode) -> TreeDiff {
-    let mut buf = FxHashMap::default();
-    // FIXME: this is both horrible inefficient and gives larger than
-    // necessary diff. I bet there's a cool algorithm to diff trees properly.
-    go(&mut buf, from.clone().into(), to.clone().into());
-    return TreeDiff { replacements: buf };
-
-    fn go(
-        buf: &mut FxHashMap<SyntaxElement, SyntaxElement>,
-        lhs: SyntaxElement,
-        rhs: SyntaxElement,
-    ) {
-        if lhs.kind() == rhs.kind()
+    let mut diff = TreeDiff {
+        replacements: FxHashMap::default(),
+        insertions: FxIndexMap::default(),
+        deletions: Vec::new(),
+    };
+    let (from, to) = (from.clone().into(), to.clone().into());
+
+    // FIXME: this is horrible inefficient. I bet there's a cool algorithm to diff trees properly.
+    if !syntax_element_eq(&from, &to) {
+        go(&mut diff, from, to);
+    }
+    return diff;
+
+    fn syntax_element_eq(lhs: &SyntaxElement, rhs: &SyntaxElement) -> bool {
+        lhs.kind() == rhs.kind()
             && lhs.text_range().len() == rhs.text_range().len()
             && match (&lhs, &rhs) {
                 (NodeOrToken::Node(lhs), NodeOrToken::Node(rhs)) => {
@@ -150,18 +167,47 @@ pub fn diff(from: &SyntaxNode, to: &SyntaxNode) -> TreeDiff {
                 (NodeOrToken::Token(lhs), NodeOrToken::Token(rhs)) => lhs.text() == rhs.text(),
                 _ => false,
             }
-        {
-            return;
-        }
-        if let (Some(lhs), Some(rhs)) = (lhs.as_node(), rhs.as_node()) {
-            if lhs.children_with_tokens().count() == rhs.children_with_tokens().count() {
-                for (lhs, rhs) in lhs.children_with_tokens().zip(rhs.children_with_tokens()) {
-                    go(buf, lhs, rhs)
-                }
+    }
+
+    fn go(diff: &mut TreeDiff, lhs: SyntaxElement, rhs: SyntaxElement) {
+        let (lhs, rhs) = match lhs.as_node().zip(rhs.as_node()) {
+            Some((lhs, rhs)) => (lhs, rhs),
+            _ => {
+                mark::hit!(diff_node_token_replace);
+                diff.replacements.insert(lhs, rhs);
                 return;
             }
+        };
+
+        let mut rhs_children = rhs.children_with_tokens();
+        let mut lhs_children = lhs.children_with_tokens();
+        let mut last_lhs = None;
+        loop {
+            let lhs_child = lhs_children.next();
+            match (lhs_child.clone(), rhs_children.next()) {
+                (None, None) => break,
+                (None, Some(element)) => match last_lhs.clone() {
+                    Some(prev) => {
+                        mark::hit!(diff_insert);
+                        diff.insertions.entry(prev).or_insert_with(Vec::new).push(element);
+                    }
+                    // first iteration, this means we got no anchor element to insert after
+                    // therefor replace the parent node instead
+                    None => {
+                        mark::hit!(diff_replace_parent);
+                        diff.replacements.insert(lhs.clone().into(), rhs.clone().into());
+                        break;
+                    }
+                },
+                (Some(element), None) => {
+                    mark::hit!(diff_delete);
+                    diff.deletions.push(element);
+                }
+                (Some(ref lhs_ele), Some(ref rhs_ele)) if syntax_element_eq(lhs_ele, rhs_ele) => {}
+                (Some(lhs_ele), Some(rhs_ele)) => go(diff, lhs_ele, rhs_ele),
+            }
+            last_lhs = lhs_child.or(last_lhs);
         }
-        buf.insert(lhs, rhs);
     }
 }
 
@@ -243,11 +289,19 @@ fn _replace_children(
     with_children(parent, new_children)
 }
 
+#[derive(Debug, PartialEq, Eq, Hash)]
+enum InsertPos {
+    FirstChildOf(SyntaxNode),
+    // Before(SyntaxElement),
+    After(SyntaxElement),
+}
+
 #[derive(Default)]
 pub struct SyntaxRewriter<'a> {
     f: Option<Box<dyn Fn(&SyntaxElement) -> Option<SyntaxElement> + 'a>>,
     //FIXME: add debug_assertions that all elements are in fact from the same file.
     replacements: FxHashMap<SyntaxElement, Replacement>,
+    insertions: IndexMap<InsertPos, Vec<SyntaxElement>>,
 }
 
 impl fmt::Debug for SyntaxRewriter<'_> {
@@ -258,13 +312,96 @@ impl fmt::Debug for SyntaxRewriter<'_> {
 
 impl<'a> SyntaxRewriter<'a> {
     pub fn from_fn(f: impl Fn(&SyntaxElement) -> Option<SyntaxElement> + 'a) -> SyntaxRewriter<'a> {
-        SyntaxRewriter { f: Some(Box::new(f)), replacements: FxHashMap::default() }
+        SyntaxRewriter {
+            f: Some(Box::new(f)),
+            replacements: FxHashMap::default(),
+            insertions: IndexMap::default(),
+        }
     }
     pub fn delete<T: Clone + Into<SyntaxElement>>(&mut self, what: &T) {
         let what = what.clone().into();
         let replacement = Replacement::Delete;
         self.replacements.insert(what, replacement);
     }
+    pub fn insert_before<T: Clone + Into<SyntaxElement>, U: Clone + Into<SyntaxElement>>(
+        &mut self,
+        before: &T,
+        what: &U,
+    ) {
+        let before = before.clone().into();
+        let pos = match before.prev_sibling_or_token() {
+            Some(sibling) => InsertPos::After(sibling),
+            None => match before.parent() {
+                Some(parent) => InsertPos::FirstChildOf(parent),
+                None => return,
+            },
+        };
+        self.insertions.entry(pos).or_insert_with(Vec::new).push(what.clone().into());
+    }
+    pub fn insert_after<T: Clone + Into<SyntaxElement>, U: Clone + Into<SyntaxElement>>(
+        &mut self,
+        after: &T,
+        what: &U,
+    ) {
+        self.insertions
+            .entry(InsertPos::After(after.clone().into()))
+            .or_insert_with(Vec::new)
+            .push(what.clone().into());
+    }
+    pub fn insert_as_first_child<T: Clone + Into<SyntaxNode>, U: Clone + Into<SyntaxElement>>(
+        &mut self,
+        parent: &T,
+        what: &U,
+    ) {
+        self.insertions
+            .entry(InsertPos::FirstChildOf(parent.clone().into()))
+            .or_insert_with(Vec::new)
+            .push(what.clone().into());
+    }
+    pub fn insert_many_before<
+        T: Clone + Into<SyntaxElement>,
+        U: IntoIterator<Item = SyntaxElement>,
+    >(
+        &mut self,
+        before: &T,
+        what: U,
+    ) {
+        let before = before.clone().into();
+        let pos = match before.prev_sibling_or_token() {
+            Some(sibling) => InsertPos::After(sibling),
+            None => match before.parent() {
+                Some(parent) => InsertPos::FirstChildOf(parent),
+                None => return,
+            },
+        };
+        self.insertions.entry(pos).or_insert_with(Vec::new).extend(what);
+    }
+    pub fn insert_many_after<
+        T: Clone + Into<SyntaxElement>,
+        U: IntoIterator<Item = SyntaxElement>,
+    >(
+        &mut self,
+        after: &T,
+        what: U,
+    ) {
+        self.insertions
+            .entry(InsertPos::After(after.clone().into()))
+            .or_insert_with(Vec::new)
+            .extend(what);
+    }
+    pub fn insert_many_as_first_children<
+        T: Clone + Into<SyntaxNode>,
+        U: IntoIterator<Item = SyntaxElement>,
+    >(
+        &mut self,
+        parent: &T,
+        what: U,
+    ) {
+        self.insertions
+            .entry(InsertPos::FirstChildOf(parent.clone().into()))
+            .or_insert_with(Vec::new)
+            .extend(what)
+    }
     pub fn replace<T: Clone + Into<SyntaxElement>>(&mut self, what: &T, with: &T) {
         let what = what.clone().into();
         let replacement = Replacement::Single(with.clone().into());
@@ -284,7 +421,7 @@ impl<'a> SyntaxRewriter<'a> {
     }
 
     pub fn rewrite(&self, node: &SyntaxNode) -> SyntaxNode {
-        if self.f.is_none() && self.replacements.is_empty() {
+        if self.f.is_none() && self.replacements.is_empty() && self.insertions.is_empty() {
             return node.clone();
         }
         self.rewrite_children(node)
@@ -300,14 +437,22 @@ impl<'a> SyntaxRewriter<'a> {
     ///
     /// Returns `None` when there are no replacements.
     pub fn rewrite_root(&self) -> Option<SyntaxNode> {
+        fn element_to_node_or_parent(element: &SyntaxElement) -> SyntaxNode {
+            match element {
+                SyntaxElement::Node(it) => it.clone(),
+                SyntaxElement::Token(it) => it.parent(),
+            }
+        }
+
         assert!(self.f.is_none());
         self.replacements
             .keys()
-            .map(|element| match element {
-                SyntaxElement::Node(it) => it.clone(),
-                SyntaxElement::Token(it) => it.parent(),
-            })
-            // If we only have one replacement, we must return its parent node, since `rewrite` does
+            .map(element_to_node_or_parent)
+            .chain(self.insertions.keys().map(|pos| match pos {
+                InsertPos::FirstChildOf(it) => it.clone(),
+                InsertPos::After(it) => element_to_node_or_parent(it),
+            }))
+            // If we only have one replacement/insertion, we must return its parent node, since `rewrite` does
             // not replace the node passed to it.
             .map(|it| it.parent().unwrap_or(it))
             .fold1(|a, b| least_common_ancestor(&a, &b).unwrap())
@@ -321,9 +466,16 @@ impl<'a> SyntaxRewriter<'a> {
         self.replacements.get(element).cloned()
     }
 
+    fn insertions(&self, pos: &InsertPos) -> Option<impl Iterator<Item = SyntaxElement> + '_> {
+        self.insertions.get(pos).map(|insertions| insertions.iter().cloned())
+    }
+
     fn rewrite_children(&self, node: &SyntaxNode) -> SyntaxNode {
         //  FIXME: this could be made much faster.
         let mut new_children = Vec::new();
+        if let Some(elements) = self.insertions(&InsertPos::FirstChildOf(node.clone())) {
+            new_children.extend(elements.map(element_to_green));
+        }
         for child in node.children_with_tokens() {
             self.rewrite_self(&mut new_children, &child);
         }
@@ -337,34 +489,45 @@ impl<'a> SyntaxRewriter<'a> {
     ) {
         if let Some(replacement) = self.replacement(&element) {
             match replacement {
-                Replacement::Single(NodeOrToken::Node(it)) => {
-                    acc.push(NodeOrToken::Node(it.green().clone()))
-                }
-                Replacement::Single(NodeOrToken::Token(it)) => {
-                    acc.push(NodeOrToken::Token(it.green().clone()))
-                }
+                Replacement::Single(element) => acc.push(element_to_green(element)),
                 Replacement::Many(replacements) => {
-                    acc.extend(replacements.iter().map(|it| match it {
-                        NodeOrToken::Node(it) => NodeOrToken::Node(it.green().clone()),
-                        NodeOrToken::Token(it) => NodeOrToken::Token(it.green().clone()),
-                    }))
+                    acc.extend(replacements.into_iter().map(element_to_green))
                 }
                 Replacement::Delete => (),
             };
-            return;
+        } else {
+            match element {
+                NodeOrToken::Token(it) => acc.push(NodeOrToken::Token(it.green().clone())),
+                NodeOrToken::Node(it) => {
+                    acc.push(NodeOrToken::Node(self.rewrite_children(it).green().clone()));
+                }
+            }
+        }
+        if let Some(elements) = self.insertions(&InsertPos::After(element.clone())) {
+            acc.extend(elements.map(element_to_green));
         }
-        let res = match element {
-            NodeOrToken::Token(it) => NodeOrToken::Token(it.green().clone()),
-            NodeOrToken::Node(it) => NodeOrToken::Node(self.rewrite_children(it).green().clone()),
-        };
-        acc.push(res)
+    }
+}
+
+fn element_to_green(element: SyntaxElement) -> NodeOrToken<rowan::GreenNode, rowan::GreenToken> {
+    match element {
+        NodeOrToken::Node(it) => NodeOrToken::Node(it.green().clone()),
+        NodeOrToken::Token(it) => NodeOrToken::Token(it.green().clone()),
     }
 }
 
 impl ops::AddAssign for SyntaxRewriter<'_> {
     fn add_assign(&mut self, rhs: SyntaxRewriter) {
         assert!(rhs.f.is_none());
-        self.replacements.extend(rhs.replacements)
+        self.replacements.extend(rhs.replacements);
+        for (pos, insertions) in rhs.insertions.into_iter() {
+            match self.insertions.entry(pos) {
+                indexmap::map::Entry::Occupied(mut occupied) => {
+                    occupied.get_mut().extend(insertions)
+                }
+                indexmap::map::Entry::Vacant(vacant) => drop(vacant.insert(insertions)),
+            }
+        }
     }
 }
 
@@ -404,3 +567,322 @@ fn to_green_element(element: SyntaxElement) -> NodeOrToken<rowan::GreenNode, row
         NodeOrToken::Token(it) => it.green().clone().into(),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use expect_test::{expect, Expect};
+    use itertools::Itertools;
+    use parser::SyntaxKind;
+    use test_utils::mark;
+    use text_edit::TextEdit;
+
+    use crate::{AstNode, SyntaxElement};
+
+    #[test]
+    fn replace_node_token() {
+        mark::check!(diff_node_token_replace);
+        check_diff(
+            r#"use node;"#,
+            r#"ident"#,
+            expect![[r#"
+                insertions:
+
+
+
+                replacements:
+
+                Line 0: Token([email protected] "use") -> ident
+
+                deletions:
+
+                Line 1: " "
+                Line 1: node
+                Line 1: ;
+            "#]],
+        );
+    }
+
+    #[test]
+    fn insert() {
+        mark::check!(diff_insert);
+        check_diff(
+            r#"use foo;"#,
+            r#"use foo;
+use bar;"#,
+            expect![[r#"
+                insertions:
+
+                Line 0: Node([email protected])
+                -> "\n"
+                -> use bar;
+
+                replacements:
+
+
+
+                deletions:
+
+
+            "#]],
+        );
+    }
+
+    #[test]
+    fn replace_parent() {
+        mark::check!(diff_replace_parent);
+        check_diff(
+            r#""#,
+            r#"use foo::bar;"#,
+            expect![[r#"
+                insertions:
+
+
+
+                replacements:
+
+                Line 0: Node([email protected]) -> use foo::bar;
+
+                deletions:
+
+
+            "#]],
+        );
+    }
+
+    #[test]
+    fn delete() {
+        mark::check!(diff_delete);
+        check_diff(
+            r#"use foo;
+            use bar;"#,
+            r#"use foo;"#,
+            expect![[r#"
+                insertions:
+
+
+
+                replacements:
+
+
+
+                deletions:
+
+                Line 1: "\n            "
+                Line 2: use bar;
+            "#]],
+        );
+    }
+
+    #[test]
+    fn insert_use() {
+        check_diff(
+            r#"
+use expect_test::{expect, Expect};
+
+use crate::AstNode;
+"#,
+            r#"
+use expect_test::{expect, Expect};
+use text_edit::TextEdit;
+
+use crate::AstNode;
+"#,
+            expect![[r#"
+                insertions:
+
+                Line 4: Token([email protected] "\n")
+                -> use crate::AstNode;
+                -> "\n"
+
+                replacements:
+
+                Line 2: Token([email protected] "\n\n") -> "\n"
+                Line 4: Token([email protected] "crate") -> text_edit
+                Line 4: Token([email protected] "AstNode") -> TextEdit
+                Line 4: Token([email protected] "\n") -> "\n\n"
+
+                deletions:
+
+
+            "#]],
+        )
+    }
+
+    #[test]
+    fn remove_use() {
+        check_diff(
+            r#"
+use expect_test::{expect, Expect};
+use text_edit::TextEdit;
+
+use crate::AstNode;
+"#,
+            r#"
+use expect_test::{expect, Expect};
+
+use crate::AstNode;
+"#,
+            expect![[r#"
+                insertions:
+
+
+
+                replacements:
+
+                Line 2: Token([email protected] "\n") -> "\n\n"
+                Line 3: Node([email protected]) -> crate
+                Line 3: Token([email protected] "TextEdit") -> AstNode
+                Line 3: Token([email protected] "\n\n") -> "\n"
+
+                deletions:
+
+                Line 4: use crate::AstNode;
+                Line 5: "\n"
+            "#]],
+        )
+    }
+
+    #[test]
+    fn merge_use() {
+        check_diff(
+            r#"
+use std::{
+    fmt,
+    hash::BuildHasherDefault,
+    ops::{self, RangeInclusive},
+};
+"#,
+            r#"
+use std::fmt;
+use std::hash::BuildHasherDefault;
+use std::ops::{self, RangeInclusive};
+"#,
+            expect![[r#"
+                insertions:
+
+                Line 2: Node([email protected])
+                -> ::
+                -> fmt
+                Line 6: Token([email protected] "\n")
+                -> use std::hash::BuildHasherDefault;
+                -> "\n"
+                -> use std::ops::{self, RangeInclusive};
+                -> "\n"
+
+                replacements:
+
+                Line 2: Token([email protected] "std") -> std
+
+                deletions:
+
+                Line 2: ::
+                Line 2: {
+                    fmt,
+                    hash::BuildHasherDefault,
+                    ops::{self, RangeInclusive},
+                }
+            "#]],
+        )
+    }
+
+    #[test]
+    fn early_return_assist() {
+        check_diff(
+            r#"
+fn main() {
+    if let Ok(x) = Err(92) {
+        foo(x);
+    }
+}
+            "#,
+            r#"
+fn main() {
+    let x = match Err(92) {
+        Ok(it) => it,
+        _ => return,
+    };
+    foo(x);
+}
+            "#,
+            expect![[r#"
+                insertions:
+
+                Line 3: Node([email protected])
+                -> " "
+                -> match Err(92) {
+                        Ok(it) => it,
+                        _ => return,
+                    }
+                -> ;
+                Line 5: Token([email protected] "}")
+                -> "\n"
+                -> }
+
+                replacements:
+
+                Line 3: Token([email protected] "if") -> let
+                Line 3: Token([email protected] "let") -> x
+                Line 3: Node([email protected]) -> =
+                Line 5: Token([email protected] "\n") -> "\n    "
+                Line 5: Token([email protected] "}") -> foo(x);
+
+                deletions:
+
+                Line 3: " "
+                Line 3: Ok(x)
+                Line 3: " "
+                Line 3: =
+                Line 3: " "
+                Line 3: Err(92)
+            "#]],
+        )
+    }
+
+    fn check_diff(from: &str, to: &str, expected_diff: Expect) {
+        let from_node = crate::SourceFile::parse(from).tree().syntax().clone();
+        let to_node = crate::SourceFile::parse(to).tree().syntax().clone();
+        let diff = super::diff(&from_node, &to_node);
+
+        let line_number =
+            |syn: &SyntaxElement| from[..syn.text_range().start().into()].lines().count();
+
+        let fmt_syntax = |syn: &SyntaxElement| match syn.kind() {
+            SyntaxKind::WHITESPACE => format!("{:?}", syn.to_string()),
+            _ => format!("{}", syn),
+        };
+
+        let insertions = diff.insertions.iter().format_with("\n", |(k, v), f| {
+            f(&format!(
+                "Line {}: {:?}\n-> {}",
+                line_number(k),
+                k,
+                v.iter().format_with("\n-> ", |v, f| f(&fmt_syntax(v)))
+            ))
+        });
+
+        let replacements = diff
+            .replacements
+            .iter()
+            .sorted_by_key(|(syntax, _)| syntax.text_range().start())
+            .format_with("\n", |(k, v), f| {
+                f(&format!("Line {}: {:?} -> {}", line_number(k), k, fmt_syntax(v)))
+            });
+
+        let deletions = diff
+            .deletions
+            .iter()
+            .format_with("\n", |v, f| f(&format!("Line {}: {}", line_number(v), &fmt_syntax(v))));
+
+        let actual = format!(
+            "insertions:\n\n{}\n\nreplacements:\n\n{}\n\ndeletions:\n\n{}\n",
+            insertions, replacements, deletions
+        );
+        expected_diff.assert_eq(&actual);
+
+        let mut from = from.to_owned();
+        let mut text_edit = TextEdit::builder();
+        diff.into_text_edit(&mut text_edit);
+        text_edit.finish().apply(&mut from);
+        assert_eq!(&*from, to, "diff did not turn `from` to `to`");
+    }
+}
diff --git a/crates/syntax/src/ast/node_ext.rs b/crates/syntax/src/ast/node_ext.rs
index 50c1c157d..c5cd1c504 100644
--- a/crates/syntax/src/ast/node_ext.rs
+++ b/crates/syntax/src/ast/node_ext.rs
@@ -7,7 +7,7 @@ use itertools::Itertools;
 use parser::SyntaxKind;
 
 use crate::{
-    ast::{self, support, AstNode, NameOwner, SyntaxNode},
+    ast::{self, support, token_ext::HasStringValue, AstNode, AstToken, NameOwner, SyntaxNode},
     SmolStr, SyntaxElement, SyntaxToken, T,
 };
 
@@ -53,8 +53,16 @@ impl ast::Attr {
     pub fn as_simple_key_value(&self) -> Option<(SmolStr, SmolStr)> {
         let lit = self.literal()?;
         let key = self.simple_name()?;
-        // FIXME: escape? raw string?
-        let value = lit.syntax().first_token()?.text().trim_matches('"').into();
+        let value_token = lit.syntax().first_token()?;
+
+        let value: SmolStr = if let Some(s) = ast::String::cast(value_token.clone()) {
+            s.value()?.into()
+        } else if let Some(s) = ast::RawString::cast(value_token) {
+            s.value()?.into()
+        } else {
+            return None;
+        };
+
         Some((key, value))
     }
 
diff --git a/crates/test_utils/src/lib.rs b/crates/test_utils/src/lib.rs
index ad586c882..a49be4602 100644
--- a/crates/test_utils/src/lib.rs
+++ b/crates/test_utils/src/lib.rs
@@ -43,12 +43,12 @@ macro_rules! assert_eq_text {
         let right = $right;
         if left != right {
             if left.trim() == right.trim() {
-                eprintln!("Left:\n{:?}\n\nRight:\n{:?}\n\nWhitespace difference\n", left, right);
+                std::eprintln!("Left:\n{:?}\n\nRight:\n{:?}\n\nWhitespace difference\n", left, right);
             } else {
                 let changeset = $crate::__Changeset::new(left, right, "\n");
-                eprintln!("Left:\n{}\n\nRight:\n{}\n\nDiff:\n{}\n", left, right, changeset);
+                std::eprintln!("Left:\n{}\n\nRight:\n{}\n\nDiff:\n{}\n", left, right, changeset);
             }
-            eprintln!($($tt)*);
+            std::eprintln!($($tt)*);
             panic!("text differs");
         }
     }};