Merge #6650

6650: Make completion and assists module independent r=matklad a=SomeoneToIgnore

A follow-up of https://github.com/rust-analyzer/rust-analyzer/pull/6553#discussion_r524402907

Move the common code for both assists and completion modules into a separate crate.

Co-authored-by: Kirill Bulatov <[email protected]>

29 files changed, 304 insertions, 302 deletions

diff --git a/crates/assists/Cargo.toml b/crates/assists/Cargo.toml
index 108f656e9..3fd8327d6 100644
--- a/crates/assists/Cargo.toml
+++ b/crates/assists/Cargo.toml
@@ -12,7 +12,7 @@ doctest = false
 [dependencies]
 rustc-hash = "1.1.0"
 itertools = "0.9.0"
-either = "1.5.3"
+either = "1.6.1"
 
 stdx = { path = "../stdx", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
diff --git a/crates/assists/src/assist_config.rs b/crates/assists/src/assist_config.rs
index b24527ec4..786224cfa 100644
--- a/crates/assists/src/assist_config.rs
+++ b/crates/assists/src/assist_config.rs
@@ -5,8 +5,9 @@
 //! assists if we are allowed to.
 
 use hir::PrefixKind;
+use ide_db::helpers::insert_use::MergeBehaviour;
 
-use crate::{utils::MergeBehaviour, AssistKind};
+use crate::AssistKind;
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct AssistConfig {
diff --git a/crates/assists/src/ast_transform.rs b/crates/assists/src/ast_transform.rs
index ac72f3f02..66e4634b1 100644
--- a/crates/assists/src/ast_transform.rs
+++ b/crates/assists/src/ast_transform.rs
@@ -1,5 +1,6 @@
 //! `AstTransformer`s are functions that replace nodes in an AST and can be easily combined.
 use hir::{HirDisplay, PathResolution, SemanticsScope};
+use ide_db::helpers::mod_path_to_ast;
 use rustc_hash::FxHashMap;
 use syntax::{
     algo::SyntaxRewriter,
@@ -7,8 +8,6 @@ use syntax::{
     SyntaxNode,
 };
 
-use crate::utils::mod_path_to_ast;
-
 pub fn apply<'a, N: AstNode>(transformer: &dyn AstTransform<'a>, node: N) -> N {
     SyntaxRewriter::from_fn(|element| match element {
         syntax::SyntaxElement::Node(n) => {
diff --git a/crates/assists/src/handlers/auto_import.rs b/crates/assists/src/handlers/auto_import.rs
index d665837a2..bd5bba646 100644
--- a/crates/assists/src/handlers/auto_import.rs
+++ b/crates/assists/src/handlers/auto_import.rs
@@ -1,8 +1,11 @@
+use ide_db::helpers::{
+    insert_use::{insert_use, ImportScope},
+    mod_path_to_ast,
+};
 use syntax::ast;
 
 use crate::{
     utils::import_assets::{ImportAssets, ImportCandidate},
-    utils::{insert_use, mod_path_to_ast, ImportScope},
     AssistContext, AssistId, AssistKind, Assists, GroupLabel,
 };
 
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 cac77c49b..d85767b4e 100644
--- a/crates/assists/src/handlers/extract_struct_from_enum_variant.rs
+++ b/crates/assists/src/handlers/extract_struct_from_enum_variant.rs
@@ -2,6 +2,10 @@ use std::iter;
 
 use either::Either;
 use hir::{AsName, EnumVariant, Module, ModuleDef, Name};
+use ide_db::helpers::{
+    insert_use::{insert_use, ImportScope},
+    mod_path_to_ast,
+};
 use ide_db::{defs::Definition, search::Reference, RootDatabase};
 use rustc_hash::{FxHashMap, FxHashSet};
 use syntax::{
@@ -10,10 +14,7 @@ use syntax::{
     SourceFile, SyntaxElement, SyntaxNode, T,
 };
 
-use crate::{
-    utils::{insert_use, mod_path_to_ast, ImportScope},
-    AssistContext, AssistId, AssistKind, Assists,
-};
+use crate::{AssistContext, AssistId, AssistKind, Assists};
 
 // Assist: extract_struct_from_enum_variant
 //
@@ -236,10 +237,9 @@ fn update_reference(
 
 #[cfg(test)]
 mod tests {
-    use crate::{
-        tests::{check_assist, check_assist_not_applicable},
-        utils::FamousDefs,
-    };
+    use ide_db::helpers::FamousDefs;
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/assists/src/handlers/fill_match_arms.rs b/crates/assists/src/handlers/fill_match_arms.rs
index eda45f5b3..ef12ef0cf 100644
--- a/crates/assists/src/handlers/fill_match_arms.rs
+++ b/crates/assists/src/handlers/fill_match_arms.rs
@@ -1,13 +1,14 @@
 use std::iter;
 
 use hir::{Adt, HasSource, ModuleDef, Semantics};
+use ide_db::helpers::{mod_path_to_ast, FamousDefs};
 use ide_db::RootDatabase;
 use itertools::Itertools;
 use syntax::ast::{self, make, AstNode, MatchArm, NameOwner, Pat};
 use test_utils::mark;
 
 use crate::{
-    utils::{mod_path_to_ast, render_snippet, Cursor, FamousDefs},
+    utils::{render_snippet, Cursor},
     AssistContext, AssistId, AssistKind, Assists,
 };
 
@@ -212,12 +213,10 @@ fn build_pat(db: &RootDatabase, module: hir::Module, var: hir::EnumVariant) -> O
 
 #[cfg(test)]
 mod tests {
+    use ide_db::helpers::FamousDefs;
     use test_utils::mark;
 
-    use crate::{
-        tests::{check_assist, check_assist_not_applicable, check_assist_target},
-        utils::FamousDefs,
-    };
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     use super::fill_match_arms;
 
diff --git a/crates/assists/src/handlers/generate_from_impl_for_enum.rs b/crates/assists/src/handlers/generate_from_impl_for_enum.rs
index 674e5a175..3c374e5d9 100644
--- a/crates/assists/src/handlers/generate_from_impl_for_enum.rs
+++ b/crates/assists/src/handlers/generate_from_impl_for_enum.rs
@@ -1,8 +1,9 @@
+use ide_db::helpers::FamousDefs;
 use ide_db::RootDatabase;
 use syntax::ast::{self, AstNode, NameOwner};
 use test_utils::mark;
 
-use crate::{utils::FamousDefs, AssistContext, AssistId, AssistKind, Assists};
+use crate::{AssistContext, AssistId, AssistKind, Assists};
 
 // Assist: generate_from_impl_for_enum
 //
diff --git a/crates/assists/src/handlers/merge_imports.rs b/crates/assists/src/handlers/merge_imports.rs
index fd9c9e03c..b7e853994 100644
--- a/crates/assists/src/handlers/merge_imports.rs
+++ b/crates/assists/src/handlers/merge_imports.rs
@@ -1,3 +1,4 @@
+use ide_db::helpers::insert_use::{try_merge_imports, try_merge_trees, MergeBehaviour};
 use syntax::{
     algo::{neighbor, SyntaxRewriter},
     ast, AstNode,
@@ -5,10 +6,7 @@ use syntax::{
 
 use crate::{
     assist_context::{AssistContext, Assists},
-    utils::{
-        insert_use::{try_merge_imports, try_merge_trees},
-        next_prev, MergeBehaviour,
-    },
+    utils::next_prev,
     AssistId, AssistKind,
 };
 
diff --git a/crates/assists/src/handlers/qualify_path.rs b/crates/assists/src/handlers/qualify_path.rs
index d5bc4e574..6f9810fe8 100644
--- a/crates/assists/src/handlers/qualify_path.rs
+++ b/crates/assists/src/handlers/qualify_path.rs
@@ -1,6 +1,7 @@
 use std::iter;
 
 use hir::AsName;
+use ide_db::helpers::mod_path_to_ast;
 use ide_db::RootDatabase;
 use syntax::{
     ast,
@@ -12,7 +13,6 @@ use test_utils::mark;
 use crate::{
     assist_context::{AssistContext, Assists},
     utils::import_assets::{ImportAssets, ImportCandidate},
-    utils::mod_path_to_ast,
     AssistId, AssistKind, GroupLabel,
 };
 
diff --git a/crates/assists/src/handlers/replace_derive_with_manual_impl.rs b/crates/assists/src/handlers/replace_derive_with_manual_impl.rs
index 453a6cebf..4d6a1956b 100644
--- a/crates/assists/src/handlers/replace_derive_with_manual_impl.rs
+++ b/crates/assists/src/handlers/replace_derive_with_manual_impl.rs
@@ -1,3 +1,4 @@
+use ide_db::helpers::mod_path_to_ast;
 use ide_db::imports_locator;
 use itertools::Itertools;
 use syntax::{
@@ -10,8 +11,7 @@ use syntax::{
 use crate::{
     assist_context::{AssistBuilder, AssistContext, Assists},
     utils::{
-        add_trait_assoc_items_to_impl, filter_assoc_items, mod_path_to_ast, render_snippet, Cursor,
-        DefaultMethods,
+        add_trait_assoc_items_to_impl, filter_assoc_items, render_snippet, Cursor, DefaultMethods,
     },
     AssistId, AssistKind,
 };
diff --git a/crates/assists/src/handlers/replace_qualified_name_with_use.rs b/crates/assists/src/handlers/replace_qualified_name_with_use.rs
index a66db9ae3..8bdf9eea5 100644
--- a/crates/assists/src/handlers/replace_qualified_name_with_use.rs
+++ b/crates/assists/src/handlers/replace_qualified_name_with_use.rs
@@ -1,10 +1,8 @@
+use ide_db::helpers::insert_use::{insert_use, ImportScope};
 use syntax::{algo::SyntaxRewriter, ast, match_ast, AstNode, SyntaxNode};
 use test_utils::mark;
 
-use crate::{
-    utils::{insert_use, ImportScope},
-    AssistContext, AssistId, AssistKind, Assists,
-};
+use crate::{AssistContext, AssistId, AssistKind, Assists};
 
 // Assist: replace_qualified_name_with_use
 //
diff --git a/crates/assists/src/utils.rs b/crates/assists/src/utils.rs
index 048746587..01f5c291f 100644
--- a/crates/assists/src/utils.rs
+++ b/crates/assists/src/utils.rs
@@ -1,10 +1,9 @@
 //! Assorted functions shared by several assists.
-pub(crate) mod insert_use;
 pub(crate) mod import_assets;
 
 use std::ops;
 
-use hir::{Crate, Enum, HasSource, Module, ScopeDef, Semantics, Trait};
+use hir::HasSource;
 use ide_db::RootDatabase;
 use itertools::Itertools;
 use syntax::{
@@ -22,30 +21,6 @@ use crate::{
     ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
 };
 
-pub use insert_use::{insert_use, ImportScope, MergeBehaviour};
-
-pub fn mod_path_to_ast(path: &hir::ModPath) -> ast::Path {
-    let _p = profile::span("mod_path_to_ast");
-    let mut segments = Vec::new();
-    let mut is_abs = false;
-    match path.kind {
-        hir::PathKind::Plain => {}
-        hir::PathKind::Super(0) => segments.push(make::path_segment_self()),
-        hir::PathKind::Super(n) => segments.extend((0..n).map(|_| make::path_segment_super())),
-        hir::PathKind::DollarCrate(_) | hir::PathKind::Crate => {
-            segments.push(make::path_segment_crate())
-        }
-        hir::PathKind::Abs => is_abs = true,
-    }
-
-    segments.extend(
-        path.segments
-            .iter()
-            .map(|segment| make::path_segment(make::name_ref(&segment.to_string()))),
-    );
-    make::path_from_segments(segments, is_abs)
-}
-
 pub(crate) fn unwrap_trivial_block(block: ast::BlockExpr) -> ast::Expr {
     extract_trivial_expression(&block)
         .filter(|expr| !expr.syntax().text().contains_char('\n'))
@@ -260,179 +235,6 @@ fn invert_special_case(expr: &ast::Expr) -> Option<ast::Expr> {
     }
 }
 
-/// 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
-/// the compiler itself as well.
-pub struct FamousDefs<'a, 'b>(pub &'a Semantics<'b, RootDatabase>, pub Option<Crate>);
-
-#[allow(non_snake_case)]
-impl FamousDefs<'_, '_> {
-    pub const FIXTURE: &'static str = r#"//- /libcore.rs crate:core
-pub mod convert {
-    pub trait From<T> {
-        fn from(t: T) -> Self;
-    }
-}
-
-pub mod default {
-    pub trait Default {
-       fn default() -> Self;
-    }
-}
-
-pub mod iter {
-    pub use self::traits::{collect::IntoIterator, iterator::Iterator};
-    mod traits {
-        pub(crate) mod iterator {
-            use crate::option::Option;
-            pub trait Iterator {
-                type Item;
-                fn next(&mut self) -> Option<Self::Item>;
-                fn by_ref(&mut self) -> &mut Self {
-                    self
-                }
-                fn take(self, n: usize) -> crate::iter::Take<Self> {
-                    crate::iter::Take { inner: self }
-                }
-            }
-
-            impl<I: Iterator> Iterator for &mut I {
-                type Item = I::Item;
-                fn next(&mut self) -> Option<I::Item> {
-                    (**self).next()
-                }
-            }
-        }
-        pub(crate) mod collect {
-            pub trait IntoIterator {
-                type Item;
-            }
-        }
-    }
-
-    pub use self::sources::*;
-    pub(crate) mod sources {
-        use super::Iterator;
-        use crate::option::Option::{self, *};
-        pub struct Repeat<A> {
-            element: A,
-        }
-
-        pub fn repeat<T>(elt: T) -> Repeat<T> {
-            Repeat { element: elt }
-        }
-
-        impl<A> Iterator for Repeat<A> {
-            type Item = A;
-
-            fn next(&mut self) -> Option<A> {
-                None
-            }
-        }
-    }
-
-    pub use self::adapters::*;
-    pub(crate) mod adapters {
-        use super::Iterator;
-        use crate::option::Option::{self, *};
-        pub struct Take<I> { pub(crate) inner: I }
-        impl<I> Iterator for Take<I> where I: Iterator {
-            type Item = <I as Iterator>::Item;
-            fn next(&mut self) -> Option<<I as Iterator>::Item> {
-                None
-            }
-        }
-    }
-}
-
-pub mod option {
-    pub enum Option<T> { None, Some(T)}
-}
-
-pub mod prelude {
-    pub use crate::{convert::From, iter::{IntoIterator, Iterator}, option::Option::{self, *}, default::Default};
-}
-#[prelude_import]
-pub use prelude::*;
-"#;
-
-    pub fn core(&self) -> Option<Crate> {
-        self.find_crate("core")
-    }
-
-    pub(crate) fn core_convert_From(&self) -> Option<Trait> {
-        self.find_trait("core:convert:From")
-    }
-
-    pub(crate) fn core_option_Option(&self) -> Option<Enum> {
-        self.find_enum("core:option:Option")
-    }
-
-    pub fn core_default_Default(&self) -> Option<Trait> {
-        self.find_trait("core:default:Default")
-    }
-
-    pub fn core_iter_Iterator(&self) -> Option<Trait> {
-        self.find_trait("core:iter:traits:iterator:Iterator")
-    }
-
-    pub fn core_iter(&self) -> Option<Module> {
-        self.find_module("core:iter")
-    }
-
-    fn find_trait(&self, path: &str) -> Option<Trait> {
-        match self.find_def(path)? {
-            hir::ScopeDef::ModuleDef(hir::ModuleDef::Trait(it)) => Some(it),
-            _ => None,
-        }
-    }
-
-    fn find_enum(&self, path: &str) -> Option<Enum> {
-        match self.find_def(path)? {
-            hir::ScopeDef::ModuleDef(hir::ModuleDef::Adt(hir::Adt::Enum(it))) => Some(it),
-            _ => None,
-        }
-    }
-
-    fn find_module(&self, path: &str) -> Option<Module> {
-        match self.find_def(path)? {
-            hir::ScopeDef::ModuleDef(hir::ModuleDef::Module(it)) => Some(it),
-            _ => None,
-        }
-    }
-
-    fn find_crate(&self, name: &str) -> Option<Crate> {
-        let krate = self.1?;
-        let db = self.0.db;
-        let res =
-            krate.dependencies(db).into_iter().find(|dep| dep.name.to_string() == name)?.krate;
-        Some(res)
-    }
-
-    fn find_def(&self, path: &str) -> Option<ScopeDef> {
-        let db = self.0.db;
-        let mut path = path.split(':');
-        let trait_ = path.next_back()?;
-        let std_crate = path.next()?;
-        let std_crate = self.find_crate(std_crate)?;
-        let mut module = std_crate.root_module(db);
-        for segment in path {
-            module = module.children(db).find_map(|child| {
-                let name = child.name(db)?;
-                if name.to_string() == segment {
-                    Some(child)
-                } else {
-                    None
-                }
-            })?;
-        }
-        let def =
-            module.scope(db, None).into_iter().find(|(name, _def)| name.to_string() == trait_)?.1;
-        Some(def)
-    }
-}
-
 pub(crate) fn next_prev() -> impl Iterator<Item = Direction> {
     [Direction::Next, Direction::Prev].iter().copied()
 }
diff --git a/crates/completion/Cargo.toml b/crates/completion/Cargo.toml
index e7df9d955..35e169a28 100644
--- a/crates/completion/Cargo.toml
+++ b/crates/completion/Cargo.toml
@@ -15,7 +15,6 @@ log = "0.4.8"
 rustc-hash = "1.1.0"
 either = "1.6.1"
 
-assists = { path = "../assists", version = "0.0.0" }
 stdx = { path = "../stdx", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
 text_edit = { path = "../text_edit", version = "0.0.0" }
diff --git a/crates/completion/src/completions/record.rs b/crates/completion/src/completions/record.rs
index 2049b9d09..eaa44c97d 100644
--- a/crates/completion/src/completions/record.rs
+++ b/crates/completion/src/completions/record.rs
@@ -1,5 +1,5 @@
 //! Complete fields in record literals and patterns.
-use assists::utils::FamousDefs;
+use ide_db::helpers::FamousDefs;
 use syntax::ast::Expr;
 
 use crate::{
@@ -45,8 +45,8 @@ pub(crate) fn complete_record(acc: &mut Completions, ctx: &CompletionContext) ->
 
 #[cfg(test)]
 mod tests {
-    use assists::utils::FamousDefs;
     use expect_test::{expect, Expect};
+    use ide_db::helpers::FamousDefs;
 
     use crate::{test_utils::completion_list, CompletionKind};
 
diff --git a/crates/completion/src/completions/unqualified_path.rs b/crates/completion/src/completions/unqualified_path.rs
index 3bd776905..81691cd7f 100644
--- a/crates/completion/src/completions/unqualified_path.rs
+++ b/crates/completion/src/completions/unqualified_path.rs
@@ -1,8 +1,8 @@
 //! Completion of names from the current scope, e.g. locals and imported items.
 
-use assists::utils::ImportScope;
 use either::Either;
 use hir::{Adt, ModuleDef, ScopeDef, Type};
+use ide_db::helpers::insert_use::ImportScope;
 use ide_db::imports_locator;
 use syntax::AstNode;
 use test_utils::mark;
diff --git a/crates/completion/src/config.rs b/crates/completion/src/config.rs
index f50735372..654a76f7b 100644
--- a/crates/completion/src/config.rs
+++ b/crates/completion/src/config.rs
@@ -4,7 +4,7 @@
 //! module, and we use to statically check that we only produce snippet
 //! completions if we are allowed to.
 
-use assists::utils::MergeBehaviour;
+use ide_db::helpers::insert_use::MergeBehaviour;
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct CompletionConfig {
diff --git a/crates/completion/src/item.rs b/crates/completion/src/item.rs
index 7b62c2c4e..e85549fef 100644
--- a/crates/completion/src/item.rs
+++ b/crates/completion/src/item.rs
@@ -2,8 +2,11 @@
 
 use std::fmt;
 
-use assists::utils::{insert_use, mod_path_to_ast, ImportScope, MergeBehaviour};
 use hir::{Documentation, ModPath, Mutability};
+use ide_db::helpers::{
+    insert_use::{self, ImportScope, MergeBehaviour},
+    mod_path_to_ast,
+};
 use syntax::{algo, TextRange};
 use text_edit::TextEdit;
 
@@ -201,7 +204,7 @@ impl CompletionItem {
             trigger_call_info: None,
             score: None,
             ref_match: None,
-            import_data: None,
+            import_to_add: None,
         }
     }
 
@@ -255,13 +258,21 @@ impl CompletionItem {
     }
 }
 
+/// An extra import to add after the completion is applied.
+#[derive(Clone)]
+pub(crate) struct ImportToAdd {
+    pub(crate) import_path: ModPath,
+    pub(crate) import_scope: ImportScope,
+    pub(crate) merge_behaviour: Option<MergeBehaviour>,
+}
+
 /// A helper to make `CompletionItem`s.
 #[must_use]
 #[derive(Clone)]
 pub(crate) struct Builder {
     source_range: TextRange,
     completion_kind: CompletionKind,
-    import_data: Option<(ModPath, ImportScope, Option<MergeBehaviour>)>,
+    import_to_add: Option<ImportToAdd>,
     label: String,
     insert_text: Option<String>,
     insert_text_format: InsertTextFormat,
@@ -285,9 +296,9 @@ impl Builder {
         let mut insert_text = self.insert_text;
         let mut text_edits = TextEdit::builder();
 
-        if let Some((import_path, import_scope, merge_behaviour)) = self.import_data {
-            let import = mod_path_to_ast(&import_path);
-            let mut import_path_without_last_segment = import_path;
+        if let Some(import_data) = self.import_to_add {
+            let import = mod_path_to_ast(&import_data.import_path);
+            let mut import_path_without_last_segment = import_data.import_path;
             let _ = import_path_without_last_segment.segments.pop();
 
             if !import_path_without_last_segment.segments.is_empty() {
@@ -300,7 +311,11 @@ impl Builder {
                 label = format!("{}::{}", import_path_without_last_segment, label);
             }
 
-            let rewriter = insert_use(&import_scope, import, merge_behaviour);
+            let rewriter = insert_use::insert_use(
+                &import_data.import_scope,
+                import,
+                import_data.merge_behaviour,
+            );
             if let Some(old_ast) = rewriter.rewrite_root() {
                 algo::diff(&old_ast, &rewriter.rewrite(&old_ast)).into_text_edit(&mut text_edits);
             }
@@ -392,11 +407,8 @@ impl Builder {
         self.trigger_call_info = Some(true);
         self
     }
-    pub(crate) fn import_data(
-        mut self,
-        import_data: Option<(ModPath, ImportScope, Option<MergeBehaviour>)>,
-    ) -> Builder {
-        self.import_data = import_data;
+    pub(crate) fn add_import(mut self, import_to_add: Option<ImportToAdd>) -> Builder {
+        self.import_to_add = import_to_add;
         self
     }
     pub(crate) fn set_ref_match(
diff --git a/crates/completion/src/render.rs b/crates/completion/src/render.rs
index bce02f577..504757a6a 100644
--- a/crates/completion/src/render.rs
+++ b/crates/completion/src/render.rs
@@ -9,15 +9,15 @@ pub(crate) mod type_alias;
 
 mod builder_ext;
 
-use assists::utils::{ImportScope, MergeBehaviour};
 use hir::{Documentation, HasAttrs, HirDisplay, ModPath, Mutability, ScopeDef, Type};
+use ide_db::helpers::insert_use::{ImportScope, MergeBehaviour};
 use ide_db::RootDatabase;
 use syntax::TextRange;
 use test_utils::mark;
 
 use crate::{
-    config::SnippetCap, CompletionContext, CompletionItem, CompletionItemKind, CompletionKind,
-    CompletionScore,
+    config::SnippetCap, item::ImportToAdd, CompletionContext, CompletionItem, CompletionItemKind,
+    CompletionKind, CompletionScore,
 };
 
 use crate::render::{enum_variant::render_enum_variant, function::render_fn, macro_::render_macro};
@@ -48,15 +48,15 @@ pub(crate) fn render_resolution<'a>(
 
 pub(crate) fn render_resolution_with_import<'a>(
     ctx: RenderContext<'a>,
-    import: ModPath,
+    import_path: ModPath,
     import_scope: ImportScope,
     merge_behaviour: Option<MergeBehaviour>,
     resolution: &ScopeDef,
 ) -> Option<CompletionItem> {
-    let local_name = import.segments.last()?.to_string();
+    let local_name = import_path.segments.last()?.to_string();
     Render::new(ctx).render_resolution(
         local_name,
-        Some((import, import_scope, merge_behaviour)),
+        Some(ImportToAdd { import_path, import_scope, merge_behaviour }),
         resolution,
     )
 }
@@ -147,7 +147,7 @@ impl<'a> Render<'a> {
     fn render_resolution(
         self,
         local_name: String,
-        import_data: Option<(ModPath, ImportScope, Option<MergeBehaviour>)>,
+        import_to_add: Option<ImportToAdd>,
         resolution: &ScopeDef,
     ) -> Option<CompletionItem> {
         let _p = profile::span("render_resolution");
@@ -160,15 +160,16 @@ impl<'a> Render<'a> {
 
         let kind = match resolution {
             ScopeDef::ModuleDef(Function(func)) => {
-                let item = render_fn(self.ctx, import_data, Some(local_name), *func);
+                let item = render_fn(self.ctx, import_to_add, Some(local_name), *func);
                 return Some(item);
             }
             ScopeDef::ModuleDef(EnumVariant(var)) => {
-                let item = render_enum_variant(self.ctx, import_data, Some(local_name), *var, None);
+                let item =
+                    render_enum_variant(self.ctx, import_to_add, Some(local_name), *var, None);
                 return Some(item);
             }
             ScopeDef::MacroDef(mac) => {
-                let item = render_macro(self.ctx, import_data, local_name, *mac);
+                let item = render_macro(self.ctx, import_to_add, local_name, *mac);
                 return item;
             }
 
@@ -193,7 +194,7 @@ impl<'a> Render<'a> {
                     local_name,
                 )
                 .kind(CompletionItemKind::UnresolvedReference)
-                .import_data(import_data)
+                .add_import(import_to_add)
                 .build();
                 return Some(item);
             }
@@ -248,7 +249,7 @@ impl<'a> Render<'a> {
 
         let item = item
             .kind(kind)
-            .import_data(import_data)
+            .add_import(import_to_add)
             .set_documentation(docs)
             .set_ref_match(ref_match)
             .build();
diff --git a/crates/completion/src/render/enum_variant.rs b/crates/completion/src/render/enum_variant.rs
index 64e742b77..f4bd02f25 100644
--- a/crates/completion/src/render/enum_variant.rs
+++ b/crates/completion/src/render/enum_variant.rs
@@ -1,24 +1,23 @@
 //! Renderer for `enum` variants.
 
-use assists::utils::{ImportScope, MergeBehaviour};
 use hir::{HasAttrs, HirDisplay, ModPath, StructKind};
 use itertools::Itertools;
 use test_utils::mark;
 
 use crate::{
-    item::{CompletionItem, CompletionItemKind, CompletionKind},
+    item::{CompletionItem, CompletionItemKind, CompletionKind, ImportToAdd},
     render::{builder_ext::Params, RenderContext},
 };
 
 pub(crate) fn render_enum_variant<'a>(
     ctx: RenderContext<'a>,
-    import_data: Option<(ModPath, ImportScope, Option<MergeBehaviour>)>,
+    import_to_add: Option<ImportToAdd>,
     local_name: Option<String>,
     variant: hir::EnumVariant,
     path: Option<ModPath>,
 ) -> CompletionItem {
     let _p = profile::span("render_enum_variant");
-    EnumVariantRender::new(ctx, local_name, variant, path).render(import_data)
+    EnumVariantRender::new(ctx, local_name, variant, path).render(import_to_add)
 }
 
 #[derive(Debug)]
@@ -63,10 +62,7 @@ impl<'a> EnumVariantRender<'a> {
         }
     }
 
-    fn render(
-        self,
-        import_data: Option<(ModPath, ImportScope, Option<MergeBehaviour>)>,
-    ) -> CompletionItem {
+    fn render(self, import_to_add: Option<ImportToAdd>) -> CompletionItem {
         let mut builder = CompletionItem::new(
             CompletionKind::Reference,
             self.ctx.source_range(),
@@ -75,7 +71,7 @@ impl<'a> EnumVariantRender<'a> {
         .kind(CompletionItemKind::EnumVariant)
         .set_documentation(self.variant.docs(self.ctx.db()))
         .set_deprecated(self.ctx.is_deprecated(self.variant))
-        .import_data(import_data)
+        .add_import(import_to_add)
         .detail(self.detail());
 
         if self.variant_kind == StructKind::Tuple {
diff --git a/crates/completion/src/render/function.rs b/crates/completion/src/render/function.rs
index e8b726ad6..542383d7e 100644
--- a/crates/completion/src/render/function.rs
+++ b/crates/completion/src/render/function.rs
@@ -1,22 +1,21 @@
 //! Renderer for function calls.
 
-use assists::utils::{ImportScope, MergeBehaviour};
-use hir::{HasSource, ModPath, Type};
+use hir::{HasSource, Type};
 use syntax::{ast::Fn, display::function_declaration};
 
 use crate::{
-    item::{CompletionItem, CompletionItemKind, CompletionKind},
+    item::{CompletionItem, CompletionItemKind, CompletionKind, ImportToAdd},
     render::{builder_ext::Params, RenderContext},
 };
 
 pub(crate) fn render_fn<'a>(
     ctx: RenderContext<'a>,
-    import_data: Option<(ModPath, ImportScope, Option<MergeBehaviour>)>,
+    import_to_add: Option<ImportToAdd>,
     local_name: Option<String>,
     fn_: hir::Function,
 ) -> CompletionItem {
     let _p = profile::span("render_fn");
-    FunctionRender::new(ctx, local_name, fn_).render(import_data)
+    FunctionRender::new(ctx, local_name, fn_).render(import_to_add)
 }
 
 #[derive(Debug)]
@@ -39,10 +38,7 @@ impl<'a> FunctionRender<'a> {
         FunctionRender { ctx, name, fn_, ast_node }
     }
 
-    fn render(
-        self,
-        import_data: Option<(ModPath, ImportScope, Option<MergeBehaviour>)>,
-    ) -> CompletionItem {
+    fn render(self, import_to_add: Option<ImportToAdd>) -> CompletionItem {
         let params = self.params();
         CompletionItem::new(CompletionKind::Reference, self.ctx.source_range(), self.name.clone())
             .kind(self.kind())
@@ -50,7 +46,7 @@ impl<'a> FunctionRender<'a> {
             .set_deprecated(self.ctx.is_deprecated(self.fn_))
             .detail(self.detail())
             .add_call_parens(self.ctx.completion, self.name, params)
-            .import_data(import_data)
+            .add_import(import_to_add)
             .build()
     }
 
diff --git a/crates/completion/src/render/macro_.rs b/crates/completion/src/render/macro_.rs
index 91055a296..b4ab32c6e 100644
--- a/crates/completion/src/render/macro_.rs
+++ b/crates/completion/src/render/macro_.rs
@@ -1,23 +1,22 @@
 //! Renderer for macro invocations.
 
-use assists::utils::{ImportScope, MergeBehaviour};
-use hir::{Documentation, HasSource, ModPath};
+use hir::{Documentation, HasSource};
 use syntax::display::macro_label;
 use test_utils::mark;
 
 use crate::{
-    item::{CompletionItem, CompletionItemKind, CompletionKind},
+    item::{CompletionItem, CompletionItemKind, CompletionKind, ImportToAdd},
     render::RenderContext,
 };
 
 pub(crate) fn render_macro<'a>(
     ctx: RenderContext<'a>,
-    import_data: Option<(ModPath, ImportScope, Option<MergeBehaviour>)>,
+    import_to_add: Option<ImportToAdd>,
     name: String,
     macro_: hir::MacroDef,
 ) -> Option<CompletionItem> {
     let _p = profile::span("render_macro");
-    MacroRender::new(ctx, name, macro_).render(import_data)
+    MacroRender::new(ctx, name, macro_).render(import_to_add)
 }
 
 #[derive(Debug)]
@@ -39,10 +38,7 @@ impl<'a> MacroRender<'a> {
         MacroRender { ctx, name, macro_, docs, bra, ket }
     }
 
-    fn render(
-        &self,
-        import_data: Option<(ModPath, ImportScope, Option<MergeBehaviour>)>,
-    ) -> Option<CompletionItem> {
+    fn render(&self, import_to_add: Option<ImportToAdd>) -> Option<CompletionItem> {
         // FIXME: Currently proc-macro do not have ast-node,
         // such that it does not have source
         if self.macro_.is_proc_macro() {
@@ -54,7 +50,7 @@ impl<'a> MacroRender<'a> {
                 .kind(CompletionItemKind::Macro)
                 .set_documentation(self.docs.clone())
                 .set_deprecated(self.ctx.is_deprecated(self.macro_))
-                .import_data(import_data)
+                .add_import(import_to_add)
                 .detail(self.detail());
 
         let needs_bang = self.needs_bang();
diff --git a/crates/ide/src/inlay_hints.rs b/crates/ide/src/inlay_hints.rs
index 6cfb22e13..65df7979c 100644
--- a/crates/ide/src/inlay_hints.rs
+++ b/crates/ide/src/inlay_hints.rs
@@ -1,6 +1,6 @@
-use assists::utils::FamousDefs;
 use either::Either;
 use hir::{known, Callable, HirDisplay, Semantics};
+use ide_db::helpers::FamousDefs;
 use ide_db::RootDatabase;
 use stdx::to_lower_snake_case;
 use syntax::{
@@ -427,8 +427,8 @@ fn get_callable(sema: &Semantics<RootDatabase>, expr: &ast::Expr) -> Option<hir:
 
 #[cfg(test)]
 mod tests {
-    use assists::utils::FamousDefs;
     use expect_test::{expect, Expect};
+    use ide_db::helpers::FamousDefs;
     use test_utils::extract_annotations;
 
     use crate::{fixture, inlay_hints::InlayHintsConfig};
diff --git a/crates/ide/src/lib.rs b/crates/ide/src/lib.rs
index 6288f7ea7..5244bdd61 100644
--- a/crates/ide/src/lib.rs
+++ b/crates/ide/src/lib.rs
@@ -87,9 +87,7 @@ pub use ide_db::{
     search::{Reference, ReferenceAccess, ReferenceKind},
 };
 
-pub use assists::{
-    utils::MergeBehaviour, Assist, AssistConfig, AssistId, AssistKind, ResolvedAssist,
-};
+pub use assists::{Assist, AssistConfig, AssistId, AssistKind, ResolvedAssist};
 pub use hir::{Documentation, Semantics};
 pub use ide_db::base_db::{
     Canceled, Change, CrateGraph, CrateId, Edition, FileId, FilePosition, FileRange, SourceRoot,
diff --git a/crates/ide_db/Cargo.toml b/crates/ide_db/Cargo.toml
index 72a9212f1..0ad6e1000 100644
--- a/crates/ide_db/Cargo.toml
+++ b/crates/ide_db/Cargo.toml
@@ -18,7 +18,8 @@ rayon = "1.5.0"
 fst = { version = "0.4", default-features = false }
 rustc-hash = "1.1.0"
 once_cell = "1.3.1"
-either = "1.5.3"
+either = "1.6.1"
+itertools = "0.9.0"
 
 stdx = { path = "../stdx", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
diff --git a/crates/ide_db/src/helpers.rs b/crates/ide_db/src/helpers.rs
new file mode 100644
index 000000000..d988588ff
--- /dev/null
+++ b/crates/ide_db/src/helpers.rs
@@ -0,0 +1,203 @@
+//! A module with ide helpers for high-level ide features.
+use crate::RootDatabase;
+use hir::{Crate, Enum, Module, ScopeDef, Semantics, Trait};
+use syntax::ast::{self, make};
+
+pub mod insert_use;
+
+/// Converts the mod path struct into its ast representation.
+pub fn mod_path_to_ast(path: &hir::ModPath) -> ast::Path {
+    let _p = profile::span("mod_path_to_ast");
+
+    let mut segments = Vec::new();
+    let mut is_abs = false;
+    match path.kind {
+        hir::PathKind::Plain => {}
+        hir::PathKind::Super(0) => segments.push(make::path_segment_self()),
+        hir::PathKind::Super(n) => segments.extend((0..n).map(|_| make::path_segment_super())),
+        hir::PathKind::DollarCrate(_) | hir::PathKind::Crate => {
+            segments.push(make::path_segment_crate())
+        }
+        hir::PathKind::Abs => is_abs = true,
+    }
+
+    segments.extend(
+        path.segments
+            .iter()
+            .map(|segment| make::path_segment(make::name_ref(&segment.to_string()))),
+    );
+    make::path_from_segments(segments, is_abs)
+}
+
+/// 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
+/// the compiler itself as well.
+pub struct FamousDefs<'a, 'b>(pub &'a Semantics<'b, RootDatabase>, pub Option<Crate>);
+
+#[allow(non_snake_case)]
+impl FamousDefs<'_, '_> {
+    pub const FIXTURE: &'static str = r#"//- /libcore.rs crate:core
+pub mod convert {
+    pub trait From<T> {
+        fn from(t: T) -> Self;
+    }
+}
+
+pub mod default {
+    pub trait Default {
+       fn default() -> Self;
+    }
+}
+
+pub mod iter {
+    pub use self::traits::{collect::IntoIterator, iterator::Iterator};
+    mod traits {
+        pub(crate) mod iterator {
+            use crate::option::Option;
+            pub trait Iterator {
+                type Item;
+                fn next(&mut self) -> Option<Self::Item>;
+                fn by_ref(&mut self) -> &mut Self {
+                    self
+                }
+                fn take(self, n: usize) -> crate::iter::Take<Self> {
+                    crate::iter::Take { inner: self }
+                }
+            }
+
+            impl<I: Iterator> Iterator for &mut I {
+                type Item = I::Item;
+                fn next(&mut self) -> Option<I::Item> {
+                    (**self).next()
+                }
+            }
+        }
+        pub(crate) mod collect {
+            pub trait IntoIterator {
+                type Item;
+            }
+        }
+    }
+
+    pub use self::sources::*;
+    pub(crate) mod sources {
+        use super::Iterator;
+        use crate::option::Option::{self, *};
+        pub struct Repeat<A> {
+            element: A,
+        }
+
+        pub fn repeat<T>(elt: T) -> Repeat<T> {
+            Repeat { element: elt }
+        }
+
+        impl<A> Iterator for Repeat<A> {
+            type Item = A;
+
+            fn next(&mut self) -> Option<A> {
+                None
+            }
+        }
+    }
+
+    pub use self::adapters::*;
+    pub(crate) mod adapters {
+        use super::Iterator;
+        use crate::option::Option::{self, *};
+        pub struct Take<I> { pub(crate) inner: I }
+        impl<I> Iterator for Take<I> where I: Iterator {
+            type Item = <I as Iterator>::Item;
+            fn next(&mut self) -> Option<<I as Iterator>::Item> {
+                None
+            }
+        }
+    }
+}
+
+pub mod option {
+    pub enum Option<T> { None, Some(T)}
+}
+
+pub mod prelude {
+    pub use crate::{convert::From, iter::{IntoIterator, Iterator}, option::Option::{self, *}, default::Default};
+}
+#[prelude_import]
+pub use prelude::*;
+"#;
+
+    pub fn core(&self) -> Option<Crate> {
+        self.find_crate("core")
+    }
+
+    pub fn core_convert_From(&self) -> Option<Trait> {
+        self.find_trait("core:convert:From")
+    }
+
+    pub fn core_option_Option(&self) -> Option<Enum> {
+        self.find_enum("core:option:Option")
+    }
+
+    pub fn core_default_Default(&self) -> Option<Trait> {
+        self.find_trait("core:default:Default")
+    }
+
+    pub fn core_iter_Iterator(&self) -> Option<Trait> {
+        self.find_trait("core:iter:traits:iterator:Iterator")
+    }
+
+    pub fn core_iter(&self) -> Option<Module> {
+        self.find_module("core:iter")
+    }
+
+    fn find_trait(&self, path: &str) -> Option<Trait> {
+        match self.find_def(path)? {
+            hir::ScopeDef::ModuleDef(hir::ModuleDef::Trait(it)) => Some(it),
+            _ => None,
+        }
+    }
+
+    fn find_enum(&self, path: &str) -> Option<Enum> {
+        match self.find_def(path)? {
+            hir::ScopeDef::ModuleDef(hir::ModuleDef::Adt(hir::Adt::Enum(it))) => Some(it),
+            _ => None,
+        }
+    }
+
+    fn find_module(&self, path: &str) -> Option<Module> {
+        match self.find_def(path)? {
+            hir::ScopeDef::ModuleDef(hir::ModuleDef::Module(it)) => Some(it),
+            _ => None,
+        }
+    }
+
+    fn find_crate(&self, name: &str) -> Option<Crate> {
+        let krate = self.1?;
+        let db = self.0.db;
+        let res =
+            krate.dependencies(db).into_iter().find(|dep| dep.name.to_string() == name)?.krate;
+        Some(res)
+    }
+
+    fn find_def(&self, path: &str) -> Option<ScopeDef> {
+        let db = self.0.db;
+        let mut path = path.split(':');
+        let trait_ = path.next_back()?;
+        let std_crate = path.next()?;
+        let std_crate = self.find_crate(std_crate)?;
+        let mut module = std_crate.root_module(db);
+        for segment in path {
+            module = module.children(db).find_map(|child| {
+                let name = child.name(db)?;
+                if name.to_string() == segment {
+                    Some(child)
+                } else {
+                    None
+                }
+            })?;
+        }
+        let def =
+            module.scope(db, None).into_iter().find(|(name, _def)| name.to_string() == trait_)?.1;
+        Some(def)
+    }
+}
diff --git a/crates/assists/src/utils/insert_use.rs b/crates/ide_db/src/helpers/insert_use.rs
index 304adb93d..67e800fad 100644
--- a/crates/assists/src/utils/insert_use.rs
+++ b/crates/ide_db/src/helpers/insert_use.rs
@@ -1,8 +1,8 @@
 //! Handle syntactic aspects of inserting a new `use`.
 use std::{cmp::Ordering, iter::successors};
 
+use crate::RootDatabase;
 use hir::Semantics;
-use ide_db::RootDatabase;
 use itertools::{EitherOrBoth, Itertools};
 use syntax::{
     algo::SyntaxRewriter,
@@ -22,7 +22,7 @@ pub enum ImportScope {
 }
 
 impl ImportScope {
-    pub(crate) fn from(syntax: SyntaxNode) -> Option<Self> {
+    pub fn from(syntax: SyntaxNode) -> Option<Self> {
         if let Some(module) = ast::Module::cast(syntax.clone()) {
             module.item_list().map(ImportScope::Module)
         } else if let this @ Some(_) = ast::SourceFile::cast(syntax.clone()) {
@@ -180,7 +180,7 @@ fn eq_visibility(vis0: Option<ast::Visibility>, vis1: Option<ast::Visibility>) -
     }
 }
 
-pub(crate) fn try_merge_imports(
+pub fn try_merge_imports(
     lhs: &ast::Use,
     rhs: &ast::Use,
     merge_behaviour: MergeBehaviour,
@@ -195,7 +195,7 @@ pub(crate) fn try_merge_imports(
     Some(lhs.with_use_tree(merged))
 }
 
-pub(crate) fn try_merge_trees(
+pub fn try_merge_trees(
     lhs: &ast::UseTree,
     rhs: &ast::UseTree,
     merge: MergeBehaviour,
diff --git a/crates/ide_db/src/lib.rs b/crates/ide_db/src/lib.rs
index 05139a651..fceaa089a 100644
--- a/crates/ide_db/src/lib.rs
+++ b/crates/ide_db/src/lib.rs
@@ -13,6 +13,7 @@ pub mod source_change;
 pub mod ty_filter;
 pub mod traits;
 pub mod call_info;
+pub mod helpers;
 
 use std::{fmt, sync::Arc};
 
diff --git a/crates/rust-analyzer/Cargo.toml b/crates/rust-analyzer/Cargo.toml
index 436f5041b..08559b53a 100644
--- a/crates/rust-analyzer/Cargo.toml
+++ b/crates/rust-analyzer/Cargo.toml
@@ -39,6 +39,7 @@ tracing-tree = { version = "0.1.4" }
 stdx = { path = "../stdx", version = "0.0.0" }
 flycheck = { path = "../flycheck", version = "0.0.0" }
 ide = { path = "../ide", version = "0.0.0" }
+ide_db = { path = "../ide_db", version = "0.0.0" }
 profile = { path = "../profile", version = "0.0.0" }
 project_model = { path = "../project_model", version = "0.0.0" }
 syntax = { path = "../syntax", version = "0.0.0" }
@@ -49,7 +50,6 @@ cfg = { path = "../cfg", version = "0.0.0" }
 toolchain = { path = "../toolchain", version = "0.0.0" }
 
 # This should only be used in CLI
-ide_db = { path = "../ide_db", version = "0.0.0" }
 ssr = { path = "../ssr", version = "0.0.0" }
 hir = { path = "../hir", version = "0.0.0" }
 hir_def = { path = "../hir_def", version = "0.0.0" }
diff --git a/crates/rust-analyzer/src/config.rs b/crates/rust-analyzer/src/config.rs
index a334cdb11..30299a465 100644
--- a/crates/rust-analyzer/src/config.rs
+++ b/crates/rust-analyzer/src/config.rs
@@ -11,10 +11,8 @@ use std::{convert::TryFrom, ffi::OsString, path::PathBuf};
 
 use flycheck::FlycheckConfig;
 use hir::PrefixKind;
-use ide::{
-    AssistConfig, CompletionConfig, DiagnosticsConfig, HoverConfig, InlayHintsConfig,
-    MergeBehaviour,
-};
+use ide::{AssistConfig, CompletionConfig, DiagnosticsConfig, HoverConfig, InlayHintsConfig};
+use ide_db::helpers::insert_use::MergeBehaviour;
 use lsp_types::{ClientCapabilities, MarkupKind};
 use project_model::{CargoConfig, ProjectJson, ProjectJsonData, ProjectManifest};
 use rustc_hash::FxHashSet;