8 files changed, 963 insertions, 221 deletions

diff --git a/crates/ide_db/src/assists.rs b/crates/ide_db/src/assists.rs
new file mode 100644
index 000000000..7881d8369
--- /dev/null
+++ b/crates/ide_db/src/assists.rs
@@ -0,0 +1,136 @@
+//! This module defines the `Assist` data structure. The actual assist live in
+//! the `ide_assists` downstream crate. We want to define the data structures in
+//! this low-level crate though, because `ide_diagnostics` also need them
+//! (fixits for diagnostics and assists are the same thing under the hood). We
+//! want to compile `ide_assists` and `ide_diagnostics` in parallel though, so
+//! we pull the common definitions upstream, to this crate.
+
+use std::str::FromStr;
+
+use syntax::TextRange;
+
+use crate::{label::Label, source_change::SourceChange};
+
+#[derive(Debug, Clone)]
+pub struct Assist {
+    pub id: AssistId,
+    /// Short description of the assist, as shown in the UI.
+    pub label: Label,
+    pub group: Option<GroupLabel>,
+    /// Target ranges are used to sort assists: the smaller the target range,
+    /// the more specific assist is, and so it should be sorted first.
+    pub target: TextRange,
+    /// Computing source change sometimes is much more costly then computing the
+    /// other fields. Additionally, the actual change is not required to show
+    /// the lightbulb UI, it only is needed when the user tries to apply an
+    /// assist. So, we compute it lazily: the API allow requesting assists with
+    /// or without source change. We could (and in fact, used to) distinguish
+    /// between resolved and unresolved assists at the type level, but this is
+    /// cumbersome, especially if you want to embed an assist into another data
+    /// structure, such as a diagnostic.
+    pub source_change: Option<SourceChange>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AssistKind {
+    // FIXME: does the None variant make sense? Probably not.
+    None,
+
+    QuickFix,
+    Generate,
+    Refactor,
+    RefactorExtract,
+    RefactorInline,
+    RefactorRewrite,
+}
+
+impl AssistKind {
+    pub fn contains(self, other: AssistKind) -> bool {
+        if self == other {
+            return true;
+        }
+
+        match self {
+            AssistKind::None | AssistKind::Generate => true,
+            AssistKind::Refactor => match other {
+                AssistKind::RefactorExtract
+                | AssistKind::RefactorInline
+                | AssistKind::RefactorRewrite => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+
+    pub fn name(&self) -> &str {
+        match self {
+            AssistKind::None => "None",
+            AssistKind::QuickFix => "QuickFix",
+            AssistKind::Generate => "Generate",
+            AssistKind::Refactor => "Refactor",
+            AssistKind::RefactorExtract => "RefactorExtract",
+            AssistKind::RefactorInline => "RefactorInline",
+            AssistKind::RefactorRewrite => "RefactorRewrite",
+        }
+    }
+}
+
+impl FromStr for AssistKind {
+    type Err = String;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "None" => Ok(AssistKind::None),
+            "QuickFix" => Ok(AssistKind::QuickFix),
+            "Generate" => Ok(AssistKind::Generate),
+            "Refactor" => Ok(AssistKind::Refactor),
+            "RefactorExtract" => Ok(AssistKind::RefactorExtract),
+            "RefactorInline" => Ok(AssistKind::RefactorInline),
+            "RefactorRewrite" => Ok(AssistKind::RefactorRewrite),
+            unknown => Err(format!("Unknown AssistKind: '{}'", unknown)),
+        }
+    }
+}
+
+/// Unique identifier of the assist, should not be shown to the user
+/// directly.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct AssistId(pub &'static str, pub AssistKind);
+
+/// A way to control how many asssist to resolve during the assist resolution.
+/// When an assist is resolved, its edits are calculated that might be costly to always do by default.
+#[derive(Debug)]
+pub enum AssistResolveStrategy {
+    /// No assists should be resolved.
+    None,
+    /// All assists should be resolved.
+    All,
+    /// Only a certain assist should be resolved.
+    Single(SingleResolve),
+}
+
+/// Hold the [`AssistId`] data of a certain assist to resolve.
+/// The original id object cannot be used due to a `'static` lifetime
+/// and the requirement to construct this struct dynamically during the resolve handling.
+#[derive(Debug)]
+pub struct SingleResolve {
+    /// The id of the assist.
+    pub assist_id: String,
+    // The kind of the assist.
+    pub assist_kind: AssistKind,
+}
+
+impl AssistResolveStrategy {
+    pub fn should_resolve(&self, id: &AssistId) -> bool {
+        match self {
+            AssistResolveStrategy::None => false,
+            AssistResolveStrategy::All => true,
+            AssistResolveStrategy::Single(single_resolve) => {
+                single_resolve.assist_id == id.0 && single_resolve.assist_kind == id.1
+            }
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct GroupLabel(pub String);
diff --git a/crates/ide_db/src/helpers.rs b/crates/ide_db/src/helpers.rs
index 00900cdc2..d96028cbc 100644
--- a/crates/ide_db/src/helpers.rs
+++ b/crates/ide_db/src/helpers.rs
@@ -74,12 +74,19 @@ pub fn visit_file_defs(
 /// 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.
+///
+/// Note that, by default, rust-analyzer tests **do not** include core or std
+/// libraries. If you are writing tests for functionality using [`FamousDefs`],
+/// you'd want to include [minicore](test_utils::MiniCore) declaration at the
+/// start of your tests:
+///
+/// ```
+/// //- minicore: iterator, ord, derive
+/// ```
 pub struct FamousDefs<'a, 'b>(pub &'a Semantics<'b, RootDatabase>, pub Option<Crate>);
 
 #[allow(non_snake_case)]
 impl FamousDefs<'_, '_> {
-    pub const FIXTURE: &'static str = include_str!("helpers/famous_defs_fixture.rs");
-
     pub fn std(&self) -> Option<Crate> {
         self.find_crate("std")
     }
diff --git a/crates/ide_db/src/helpers/famous_defs_fixture.rs b/crates/ide_db/src/helpers/famous_defs_fixture.rs
deleted file mode 100644
index 312851966..000000000
--- a/crates/ide_db/src/helpers/famous_defs_fixture.rs
+++ /dev/null
@@ -1,153 +0,0 @@
-//- /libcore.rs crate:core
-//! Signatures of traits, types and functions from the core lib for use in tests.
-pub mod cmp {
-
-    pub trait Ord {
-        fn cmp(&self, other: &Self) -> Ordering;
-        fn max(self, other: Self) -> Self;
-        fn min(self, other: Self) -> Self;
-        fn clamp(self, min: Self, max: Self) -> Self;
-    }
-}
-
-pub mod convert {
-    pub trait From<T> {
-        fn from(t: T) -> Self;
-    }
-
-    pub trait Into<T> {
-        pub fn into(self) -> T;
-    }
-}
-
-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 ops {
-    #[lang = "fn"]
-    pub trait Fn<Args>: FnMut<Args> {
-        extern "rust-call" fn call(&self, args: Args) -> Self::Output;
-    }
-
-    #[lang = "fn_mut"]
-    pub trait FnMut<Args>: FnOnce<Args> {
-        extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output;
-    }
-    #[lang = "fn_once"]
-    pub trait FnOnce<Args> {
-        #[lang = "fn_once_output"]
-        type Output;
-        extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
-    }
-
-    #[lang = "deref"]
-    pub trait Deref {
-        type Target: ?Sized;
-        fn deref(&self) -> &Self::Target;
-    }
-}
-
-pub mod option {
-    pub enum Option<T> {
-        None,
-        Some(T),
-    }
-}
-
-pub mod prelude {
-    pub mod rust_2018 {
-        pub use crate::{
-            cmp::Ord,
-            convert::{From, Into},
-            default::Default,
-            iter::{IntoIterator, Iterator},
-            ops::{Fn, FnMut, FnOnce},
-            option::Option::{self, *},
-        };
-    }
-}
-#[prelude_import]
-pub use prelude::rust_2018::*;
-//- /libstd.rs crate:std deps:core
-//! Signatures of traits, types and functions from the std lib for use in tests.
-
-/// Docs for return_keyword
-mod return_keyword {}
-
-/// Docs for prim_str
-mod prim_str {}
-
-pub use core::ops;
diff --git a/crates/ide_db/src/helpers/insert_use.rs b/crates/ide_db/src/helpers/insert_use.rs
index 10bbafe77..e6b4832e7 100644
--- a/crates/ide_db/src/helpers/insert_use.rs
+++ b/crates/ide_db/src/helpers/insert_use.rs
@@ -5,7 +5,7 @@ use hir::Semantics;
 use syntax::{
     algo,
     ast::{self, make, AstNode, AttrsOwner, ModuleItemOwner, PathSegmentKind, VisibilityOwner},
-    ted, AstToken, Direction, NodeOrToken, SyntaxNode, SyntaxToken,
+    match_ast, ted, AstToken, Direction, NodeOrToken, SyntaxNode, SyntaxToken,
 };
 
 use crate::{
@@ -36,22 +36,39 @@ pub struct InsertUseConfig {
     pub enforce_granularity: bool,
     pub prefix_kind: PrefixKind,
     pub group: bool,
+    pub skip_glob_imports: bool,
 }
 
 #[derive(Debug, Clone)]
 pub enum ImportScope {
     File(ast::SourceFile),
     Module(ast::ItemList),
+    Block(ast::BlockExpr),
 }
 
 impl ImportScope {
-    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()) {
-            this.map(ImportScope::File)
-        } else {
-            ast::ItemList::cast(syntax).map(ImportScope::Module)
+    fn from(syntax: SyntaxNode) -> Option<Self> {
+        fn contains_cfg_attr(attrs: &dyn AttrsOwner) -> bool {
+            attrs
+                .attrs()
+                .any(|attr| attr.as_simple_call().map_or(false, |(ident, _)| ident == "cfg"))
+        }
+        match_ast! {
+            match syntax {
+                ast::Module(module) => module.item_list().map(ImportScope::Module),
+                ast::SourceFile(file) => Some(ImportScope::File(file)),
+                ast::Fn(func) => contains_cfg_attr(&func).then(|| func.body().map(ImportScope::Block)).flatten(),
+                ast::Const(konst) => contains_cfg_attr(&konst).then(|| match konst.body()? {
+                    ast::Expr::BlockExpr(block) => Some(block),
+                    _ => None,
+                }).flatten().map(ImportScope::Block),
+                ast::Static(statik) => contains_cfg_attr(&statik).then(|| match statik.body()? {
+                    ast::Expr::BlockExpr(block) => Some(block),
+                    _ => None,
+                }).flatten().map(ImportScope::Block),
+                _ => None,
+
+            }
         }
     }
 
@@ -72,6 +89,7 @@ impl ImportScope {
         match self {
             ImportScope::File(file) => file.syntax(),
             ImportScope::Module(item_list) => item_list.syntax(),
+            ImportScope::Block(block) => block.syntax(),
         }
     }
 
@@ -79,6 +97,7 @@ impl ImportScope {
         match self {
             ImportScope::File(file) => ImportScope::File(file.clone_for_update()),
             ImportScope::Module(item_list) => ImportScope::Module(item_list.clone_for_update()),
+            ImportScope::Block(block) => ImportScope::Block(block.clone_for_update()),
         }
     }
 
@@ -95,6 +114,7 @@ impl ImportScope {
         let mut use_stmts = match self {
             ImportScope::File(f) => f.items(),
             ImportScope::Module(m) => m.items(),
+            ImportScope::Block(b) => b.items(),
         }
         .filter_map(use_stmt);
         let mut res = ImportGranularityGuess::Unknown;
@@ -153,7 +173,7 @@ enum ImportGranularityGuess {
 }
 
 /// Insert an import path into the given file/node. A `merge` value of none indicates that no import merging is allowed to occur.
-pub fn insert_use<'a>(scope: &ImportScope, path: ast::Path, cfg: InsertUseConfig) {
+pub fn insert_use<'a>(scope: &ImportScope, path: ast::Path, cfg: &InsertUseConfig) {
     let _p = profile::span("insert_use");
     let mut mb = match cfg.granularity {
         ImportGranularity::Crate => Some(MergeBehavior::Crate),
@@ -175,7 +195,10 @@ pub fn insert_use<'a>(scope: &ImportScope, path: ast::Path, cfg: InsertUseConfig
         make::use_(None, make::use_tree(path.clone(), None, None, false)).clone_for_update();
     // merge into existing imports if possible
     if let Some(mb) = mb {
-        for existing_use in scope.as_syntax_node().children().filter_map(ast::Use::cast) {
+        let filter = |it: &_| !(cfg.skip_glob_imports && ast::Use::is_simple_glob(it));
+        for existing_use in
+            scope.as_syntax_node().children().filter_map(ast::Use::cast).filter(filter)
+        {
             if let Some(merged) = try_merge_imports(&existing_use, &use_item, mb) {
                 ted::replace(existing_use.syntax(), merged.syntax());
                 return;
@@ -315,28 +338,29 @@ fn insert_use_(
         ted::insert(ted::Position::after(last_inner_element), make::tokens::single_newline());
         return;
     }
-    match scope {
+    let l_curly = match scope {
         ImportScope::File(_) => {
             cov_mark::hit!(insert_group_empty_file);
             ted::insert(ted::Position::first_child_of(scope_syntax), make::tokens::blank_line());
-            ted::insert(ted::Position::first_child_of(scope_syntax), use_item.syntax())
+            ted::insert(ted::Position::first_child_of(scope_syntax), use_item.syntax());
+            return;
         }
+        // don't insert the imports before the item list/block expr's opening curly brace
+        ImportScope::Module(item_list) => item_list.l_curly_token(),
         // don't insert the imports before the item list's opening curly brace
-        ImportScope::Module(item_list) => match item_list.l_curly_token() {
-            Some(b) => {
-                cov_mark::hit!(insert_group_empty_module);
-                ted::insert(ted::Position::after(&b), make::tokens::single_newline());
-                ted::insert(ted::Position::after(&b), use_item.syntax());
-            }
-            None => {
-                // This should never happens, broken module syntax node
-                ted::insert(
-                    ted::Position::first_child_of(scope_syntax),
-                    make::tokens::blank_line(),
-                );
-                ted::insert(ted::Position::first_child_of(scope_syntax), use_item.syntax());
-            }
-        },
+        ImportScope::Block(block) => block.l_curly_token(),
+    };
+    match l_curly {
+        Some(b) => {
+            cov_mark::hit!(insert_group_empty_module);
+            ted::insert(ted::Position::after(&b), make::tokens::single_newline());
+            ted::insert(ted::Position::after(&b), use_item.syntax());
+        }
+        None => {
+            // This should never happens, broken module syntax node
+            ted::insert(ted::Position::first_child_of(scope_syntax), make::tokens::blank_line());
+            ted::insert(ted::Position::first_child_of(scope_syntax), use_item.syntax());
+        }
     }
 }
 
diff --git a/crates/ide_db/src/helpers/insert_use/tests.rs b/crates/ide_db/src/helpers/insert_use/tests.rs
index 70b11bf81..01894630a 100644
--- a/crates/ide_db/src/helpers/insert_use/tests.rs
+++ b/crates/ide_db/src/helpers/insert_use/tests.rs
@@ -1,12 +1,63 @@
 use super::*;
 
 use hir::PrefixKind;
-use test_utils::assert_eq_text;
+use test_utils::{assert_eq_text, extract_range_or_offset, CURSOR_MARKER};
+
+#[test]
+fn respects_cfg_attr_fn() {
+    check(
+        r"bar::Bar",
+        r#"
+#[cfg(test)]
+fn foo() {$0}
+"#,
+        r#"
+#[cfg(test)]
+fn foo() {
+use bar::Bar;
+}
+"#,
+        ImportGranularity::Crate,
+    );
+}
+
+#[test]
+fn respects_cfg_attr_const() {
+    check(
+        r"bar::Bar",
+        r#"
+#[cfg(test)]
+const FOO: Bar = {$0};
+"#,
+        r#"
+#[cfg(test)]
+const FOO: Bar = {
+use bar::Bar;
+};
+"#,
+        ImportGranularity::Crate,
+    );
+}
+
+#[test]
+fn insert_skips_lone_glob_imports() {
+    check(
+        "use foo::baz::A",
+        r"
+use foo::bar::*;
+",
+        r"
+use foo::bar::*;
+use foo::baz::A;
+",
+        ImportGranularity::Crate,
+    );
+}
 
 #[test]
 fn insert_not_group() {
     cov_mark::check!(insert_no_grouping_last);
-    check(
+    check_with_config(
         "use external_crate2::bar::A",
         r"
 use std::bar::B;
@@ -21,24 +72,32 @@ use crate::bar::A;
 use self::bar::A;
 use super::bar::A;
 use external_crate2::bar::A;",
-        ImportGranularity::Item,
-        false,
-        false,
+        &InsertUseConfig {
+            granularity: ImportGranularity::Item,
+            enforce_granularity: true,
+            prefix_kind: PrefixKind::Plain,
+            group: false,
+            skip_glob_imports: true,
+        },
     );
 }
 
 #[test]
 fn insert_not_group_empty() {
     cov_mark::check!(insert_no_grouping_last2);
-    check(
+    check_with_config(
         "use external_crate2::bar::A",
         r"",
         r"use external_crate2::bar::A;
 
 ",
-        ImportGranularity::Item,
-        false,
-        false,
+        &InsertUseConfig {
+            granularity: ImportGranularity::Item,
+            enforce_granularity: true,
+            prefix_kind: PrefixKind::Plain,
+            group: false,
+            skip_glob_imports: true,
+        },
     );
 }
 
@@ -277,13 +336,15 @@ fn insert_empty_module() {
     cov_mark::check!(insert_group_empty_module);
     check(
         "foo::bar",
-        "mod x {}",
-        r"{
+        r"
+mod x {$0}
+",
+        r"
+mod x {
     use foo::bar;
-}",
+}
+",
         ImportGranularity::Item,
-        true,
-        true,
     )
 }
 
@@ -511,13 +572,14 @@ use std::io;
 }
 
 #[test]
-#[ignore] // FIXME: Support this
 fn split_out_merge() {
+    // FIXME: This is suboptimal, we want to get `use std::fmt::{self, Result}`
+    // instead.
     check_module(
         "std::fmt::Result",
         r"use std::{fmt, io};",
-        r"use std::fmt::{self, Result};
-use std::io;",
+        r"use std::fmt::Result;
+use std::{fmt, io};",
     )
 }
 
@@ -533,17 +595,35 @@ fn merge_groups_self() {
 
 #[test]
 fn merge_mod_into_glob() {
-    check_crate(
+    check_with_config(
         "token::TokenKind",
         r"use token::TokenKind::*;",
         r"use token::TokenKind::{*, self};",
+        &InsertUseConfig {
+            granularity: ImportGranularity::Crate,
+            enforce_granularity: true,
+            prefix_kind: PrefixKind::Plain,
+            group: false,
+            skip_glob_imports: false,
+        },
     )
     // FIXME: have it emit `use token::TokenKind::{self, *}`?
 }
 
 #[test]
 fn merge_self_glob() {
-    check_crate("self", r"use self::*;", r"use self::{*, self};")
+    check_with_config(
+        "self",
+        r"use self::*;",
+        r"use self::{*, self};",
+        &InsertUseConfig {
+            granularity: ImportGranularity::Crate,
+            enforce_granularity: true,
+            prefix_kind: PrefixKind::Plain,
+            group: false,
+            skip_glob_imports: false,
+        },
+    )
     // FIXME: have it emit `use {self, *}`?
 }
 
@@ -756,19 +836,24 @@ use foo::bar::qux;
     );
 }
 
-fn check(
+fn check_with_config(
     path: &str,
     ra_fixture_before: &str,
     ra_fixture_after: &str,
-    granularity: ImportGranularity,
-    module: bool,
-    group: bool,
+    config: &InsertUseConfig,
 ) {
-    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.clone_for_update()).unwrap();
+    let (text, pos) = if ra_fixture_before.contains(CURSOR_MARKER) {
+        let (range_or_offset, text) = extract_range_or_offset(ra_fixture_before);
+        (text, Some(range_or_offset))
+    } else {
+        (ra_fixture_before.to_owned(), None)
+    };
+    let syntax = ast::SourceFile::parse(&text).tree().syntax().clone_for_update();
+    let file = pos
+        .and_then(|pos| syntax.token_at_offset(pos.expect_offset()).next()?.parent())
+        .and_then(|it| super::ImportScope::find_insert_use_container(&it))
+        .or_else(|| super::ImportScope::from(syntax))
+        .unwrap();
     let path = ast::SourceFile::parse(&format!("use {};", path))
         .tree()
         .syntax()
@@ -776,30 +861,41 @@ fn check(
         .find_map(ast::Path::cast)
         .unwrap();
 
-    insert_use(
-        &file,
+    insert_use(&file, path, config);
+    let result = file.as_syntax_node().ancestors().last().unwrap().to_string();
+    assert_eq_text!(ra_fixture_after, &result);
+}
+
+fn check(
+    path: &str,
+    ra_fixture_before: &str,
+    ra_fixture_after: &str,
+    granularity: ImportGranularity,
+) {
+    check_with_config(
         path,
-        InsertUseConfig {
+        ra_fixture_before,
+        ra_fixture_after,
+        &InsertUseConfig {
             granularity,
             enforce_granularity: true,
             prefix_kind: PrefixKind::Plain,
-            group,
+            group: true,
+            skip_glob_imports: true,
         },
-    );
-    let result = file.as_syntax_node().to_string();
-    assert_eq_text!(ra_fixture_after, &result);
+    )
 }
 
 fn check_crate(path: &str, ra_fixture_before: &str, ra_fixture_after: &str) {
-    check(path, ra_fixture_before, ra_fixture_after, ImportGranularity::Crate, false, true)
+    check(path, ra_fixture_before, ra_fixture_after, ImportGranularity::Crate)
 }
 
 fn check_module(path: &str, ra_fixture_before: &str, ra_fixture_after: &str) {
-    check(path, ra_fixture_before, ra_fixture_after, ImportGranularity::Module, false, true)
+    check(path, ra_fixture_before, ra_fixture_after, ImportGranularity::Module)
 }
 
 fn check_none(path: &str, ra_fixture_before: &str, ra_fixture_after: &str) {
-    check(path, ra_fixture_before, ra_fixture_after, ImportGranularity::Item, false, true)
+    check(path, ra_fixture_before, ra_fixture_after, ImportGranularity::Item)
 }
 
 fn check_merge_only_fail(ra_fixture0: &str, ra_fixture1: &str, mb: MergeBehavior) {
diff --git a/crates/ide_db/src/lib.rs b/crates/ide_db/src/lib.rs
index 105607dca..bde8767dd 100644
--- a/crates/ide_db/src/lib.rs
+++ b/crates/ide_db/src/lib.rs
@@ -3,17 +3,21 @@
 //! It is mainly a `HirDatabase` for semantic analysis, plus a `SymbolsDatabase`, for fuzzy search.
 
 mod apply_change;
+pub mod assists;
 pub mod label;
 pub mod line_index;
 pub mod symbol_index;
 pub mod defs;
-pub mod search;
 pub mod items_locator;
 pub mod source_change;
 pub mod ty_filter;
 pub mod traits;
 pub mod call_info;
 pub mod helpers;
+pub mod path_transform;
+
+pub mod search;
+pub mod rename;
 
 use std::{fmt, sync::Arc};
 
diff --git a/crates/ide_db/src/path_transform.rs b/crates/ide_db/src/path_transform.rs
new file mode 100644
index 000000000..f3d7aa920
--- /dev/null
+++ b/crates/ide_db/src/path_transform.rs
@@ -0,0 +1,160 @@
+//! See [`PathTransform`].
+
+use crate::helpers::mod_path_to_ast;
+use hir::{HirDisplay, SemanticsScope};
+use rustc_hash::FxHashMap;
+use syntax::{
+    ast::{self, AstNode},
+    ted,
+};
+
+/// `PathTransform` substitutes path in SyntaxNodes in bulk.
+///
+/// This is mostly useful for IDE code generation. If you paste some existing
+/// code into a new context (for example, to add method overrides to an `impl`
+/// block), you generally want to appropriately qualify the names, and sometimes
+/// you might want to substitute generic parameters as well:
+///
+/// ```
+/// mod x {
+///   pub struct A<V>;
+///   pub trait T<U> { fn foo(&self, _: U) -> A<U>; }
+/// }
+///
+/// mod y {
+///   use x::T;
+///
+///   impl T<()> for () {
+///      // If we invoke **Add Missing Members** here, we want to copy-paste `foo`.
+///      // But we want a slightly-modified version of it:
+///      fn foo(&self, _: ()) -> x::A<()> {}
+///   }
+/// }
+/// ```
+pub struct PathTransform<'a> {
+    pub subst: (hir::Trait, ast::Impl),
+    pub target_scope: &'a SemanticsScope<'a>,
+    pub source_scope: &'a SemanticsScope<'a>,
+}
+
+impl<'a> PathTransform<'a> {
+    pub fn apply(&self, item: ast::AssocItem) {
+        if let Some(ctx) = self.build_ctx() {
+            ctx.apply(item)
+        }
+    }
+    fn build_ctx(&self) -> Option<Ctx<'a>> {
+        let db = self.source_scope.db;
+        let target_module = self.target_scope.module()?;
+        let source_module = self.source_scope.module()?;
+
+        let substs = get_syntactic_substs(self.subst.1.clone()).unwrap_or_default();
+        let generic_def: hir::GenericDef = self.subst.0.into();
+        let substs_by_param: FxHashMap<_, _> = generic_def
+            .type_params(db)
+            .into_iter()
+            // this is a trait impl, so we need to skip the first type parameter -- this is a bit hacky
+            .skip(1)
+            // The actual list of trait type parameters may be longer than the one
+            // used in the `impl` block due to trailing default type parameters.
+            // For that case we extend the `substs` with an empty iterator so we
+            // can still hit those trailing values and check if they actually have
+            // a default type. If they do, go for that type from `hir` to `ast` so
+            // the resulting change can be applied correctly.
+            .zip(substs.into_iter().map(Some).chain(std::iter::repeat(None)))
+            .filter_map(|(k, v)| match v {
+                Some(v) => Some((k, v)),
+                None => {
+                    let default = k.default(db)?;
+                    Some((
+                        k,
+                        ast::make::ty(&default.display_source_code(db, source_module.into()).ok()?),
+                    ))
+                }
+            })
+            .collect();
+
+        let res = Ctx { substs: substs_by_param, target_module, source_scope: self.source_scope };
+        Some(res)
+    }
+}
+
+struct Ctx<'a> {
+    substs: FxHashMap<hir::TypeParam, ast::Type>,
+    target_module: hir::Module,
+    source_scope: &'a SemanticsScope<'a>,
+}
+
+impl<'a> Ctx<'a> {
+    fn apply(&self, item: ast::AssocItem) {
+        for event in item.syntax().preorder() {
+            let node = match event {
+                syntax::WalkEvent::Enter(_) => continue,
+                syntax::WalkEvent::Leave(it) => it,
+            };
+            if let Some(path) = ast::Path::cast(node.clone()) {
+                self.transform_path(path);
+            }
+        }
+    }
+    fn transform_path(&self, path: ast::Path) -> Option<()> {
+        if path.qualifier().is_some() {
+            return None;
+        }
+        if path.segment().and_then(|s| s.param_list()).is_some() {
+            // don't try to qualify `Fn(Foo) -> Bar` paths, they are in prelude anyway
+            return None;
+        }
+
+        let resolution = self.source_scope.speculative_resolve(&path)?;
+
+        match resolution {
+            hir::PathResolution::TypeParam(tp) => {
+                if let Some(subst) = self.substs.get(&tp) {
+                    ted::replace(path.syntax(), subst.clone_subtree().clone_for_update().syntax())
+                }
+            }
+            hir::PathResolution::Def(def) => {
+                let found_path =
+                    self.target_module.find_use_path(self.source_scope.db.upcast(), def)?;
+                let res = mod_path_to_ast(&found_path).clone_for_update();
+                if let Some(args) = path.segment().and_then(|it| it.generic_arg_list()) {
+                    if let Some(segment) = res.segment() {
+                        let old = segment.get_or_create_generic_arg_list();
+                        ted::replace(old.syntax(), args.clone_subtree().syntax().clone_for_update())
+                    }
+                }
+                ted::replace(path.syntax(), res.syntax())
+            }
+            hir::PathResolution::Local(_)
+            | hir::PathResolution::ConstParam(_)
+            | hir::PathResolution::SelfType(_)
+            | hir::PathResolution::Macro(_)
+            | hir::PathResolution::AssocItem(_) => (),
+        }
+        Some(())
+    }
+}
+
+// FIXME: It would probably be nicer if we could get this via HIR (i.e. get the
+// trait ref, and then go from the types in the substs back to the syntax).
+fn get_syntactic_substs(impl_def: ast::Impl) -> Option<Vec<ast::Type>> {
+    let target_trait = impl_def.trait_()?;
+    let path_type = match target_trait {
+        ast::Type::PathType(path) => path,
+        _ => return None,
+    };
+    let generic_arg_list = path_type.path()?.segment()?.generic_arg_list()?;
+
+    let mut result = Vec::new();
+    for generic_arg in generic_arg_list.generic_args() {
+        match generic_arg {
+            ast::GenericArg::TypeArg(type_arg) => result.push(type_arg.ty()?),
+            ast::GenericArg::AssocTypeArg(_)
+            | ast::GenericArg::LifetimeArg(_)
+            | ast::GenericArg::ConstArg(_) => (),
+        }
+    }
+
+    Some(result)
+}
diff --git a/crates/ide_db/src/rename.rs b/crates/ide_db/src/rename.rs
new file mode 100644
index 000000000..643e67781
--- /dev/null
+++ b/crates/ide_db/src/rename.rs
@@ -0,0 +1,468 @@
+//! Rename infrastructure for rust-analyzer. It is used primarily for the
+//! literal "rename" in the ide (look for tests there), but it is also available
+//! as a general-purpose service. For example, it is used by the fix for the
+//! "incorrect case" diagnostic.
+//!
+//! It leverages the [`crate::search`] functionality to find what needs to be
+//! renamed. The actual renames are tricky -- field shorthands need special
+//! attention, and, when renaming modules, you also want to rename files on the
+//! file system.
+//!
+//! Another can of worms are macros:
+//!
+//! ```
+//! macro_rules! m { () => { fn f() {} } }
+//! m!();
+//! fn main() {
+//!     f() // <- rename me
+//! }
+//! ```
+//!
+//! The correct behavior in such cases is probably to show a dialog to the user.
+//! Our current behavior is ¯\_(ツ)_/¯.
+use std::fmt;
+
+use base_db::{AnchoredPathBuf, FileId, FileRange};
+use either::Either;
+use hir::{AsAssocItem, FieldSource, HasSource, InFile, ModuleSource, Semantics};
+use stdx::never;
+use syntax::{
+    ast::{self, NameOwner},
+    lex_single_syntax_kind, AstNode, SyntaxKind, TextRange, T,
+};
+use text_edit::TextEdit;
+
+use crate::{
+    defs::Definition,
+    search::FileReference,
+    source_change::{FileSystemEdit, SourceChange},
+    RootDatabase,
+};
+
+pub type Result<T, E = RenameError> = std::result::Result<T, E>;
+
+#[derive(Debug)]
+pub struct RenameError(pub String);
+
+impl fmt::Display for RenameError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.0, f)
+    }
+}
+
+#[macro_export]
+macro_rules! _format_err {
+    ($fmt:expr) => { RenameError(format!($fmt)) };
+    ($fmt:expr, $($arg:tt)+) => { RenameError(format!($fmt, $($arg)+)) }
+}
+pub use _format_err as format_err;
+
+#[macro_export]
+macro_rules! _bail {
+    ($($tokens:tt)*) => { return Err(format_err!($($tokens)*)) }
+}
+pub use _bail as bail;
+
+impl Definition {
+    pub fn rename(&self, sema: &Semantics<RootDatabase>, new_name: &str) -> Result<SourceChange> {
+        match *self {
+            Definition::ModuleDef(hir::ModuleDef::Module(module)) => {
+                rename_mod(sema, module, new_name)
+            }
+            Definition::ModuleDef(hir::ModuleDef::BuiltinType(_)) => {
+                bail!("Cannot rename builtin type")
+            }
+            Definition::SelfType(_) => bail!("Cannot rename `Self`"),
+            def => rename_reference(sema, def, new_name),
+        }
+    }
+
+    /// Textual range of the identifier which will change when renaming this
+    /// `Definition`. Note that some definitions, like buitin types, can't be
+    /// renamed.
+    pub fn range_for_rename(self, sema: &Semantics<RootDatabase>) -> Option<FileRange> {
+        // FIXME: the `original_file_range` calls here are wrong -- they never fail,
+        // and _fall back_ to the entirety of the macro call. Such fall back is
+        // incorrect for renames. The safe behavior would be to return an error for
+        // such cases. The correct behavior would be to return an auxiliary list of
+        // "can't rename these occurrences in macros" items, and then show some kind
+        // of a dialog to the user. See:
+        cov_mark::hit!(macros_are_broken_lol);
+
+        let res = match self {
+            Definition::Macro(mac) => {
+                let src = mac.source(sema.db)?;
+                let name = match &src.value {
+                    Either::Left(it) => it.name()?,
+                    Either::Right(it) => it.name()?,
+                };
+                src.with_value(name.syntax()).original_file_range(sema.db)
+            }
+            Definition::Field(field) => {
+                let src = field.source(sema.db)?;
+
+                match &src.value {
+                    FieldSource::Named(record_field) => {
+                        let name = record_field.name()?;
+                        src.with_value(name.syntax()).original_file_range(sema.db)
+                    }
+                    FieldSource::Pos(_) => {
+                        return None;
+                    }
+                }
+            }
+            Definition::ModuleDef(module_def) => match module_def {
+                hir::ModuleDef::Module(module) => {
+                    let src = module.declaration_source(sema.db)?;
+                    let name = src.value.name()?;
+                    src.with_value(name.syntax()).original_file_range(sema.db)
+                }
+                hir::ModuleDef::Function(it) => name_range(it, sema)?,
+                hir::ModuleDef::Adt(adt) => match adt {
+                    hir::Adt::Struct(it) => name_range(it, sema)?,
+                    hir::Adt::Union(it) => name_range(it, sema)?,
+                    hir::Adt::Enum(it) => name_range(it, sema)?,
+                },
+                hir::ModuleDef::Variant(it) => name_range(it, sema)?,
+                hir::ModuleDef::Const(it) => name_range(it, sema)?,
+                hir::ModuleDef::Static(it) => name_range(it, sema)?,
+                hir::ModuleDef::Trait(it) => name_range(it, sema)?,
+                hir::ModuleDef::TypeAlias(it) => name_range(it, sema)?,
+                hir::ModuleDef::BuiltinType(_) => return None,
+            },
+            Definition::SelfType(_) => return None,
+            Definition::Local(local) => {
+                let src = local.source(sema.db);
+                let name = match &src.value {
+                    Either::Left(bind_pat) => bind_pat.name()?,
+                    Either::Right(_) => return None,
+                };
+                src.with_value(name.syntax()).original_file_range(sema.db)
+            }
+            Definition::GenericParam(generic_param) => match generic_param {
+                hir::GenericParam::TypeParam(type_param) => {
+                    let src = type_param.source(sema.db)?;
+                    let name = match &src.value {
+                        Either::Left(type_param) => type_param.name()?,
+                        Either::Right(_trait) => return None,
+                    };
+                    src.with_value(name.syntax()).original_file_range(sema.db)
+                }
+                hir::GenericParam::LifetimeParam(lifetime_param) => {
+                    let src = lifetime_param.source(sema.db)?;
+                    let lifetime = src.value.lifetime()?;
+                    src.with_value(lifetime.syntax()).original_file_range(sema.db)
+                }
+                hir::GenericParam::ConstParam(it) => name_range(it, sema)?,
+            },
+            Definition::Label(label) => {
+                let src = label.source(sema.db);
+                let lifetime = src.value.lifetime()?;
+                src.with_value(lifetime.syntax()).original_file_range(sema.db)
+            }
+        };
+        return Some(res);
+
+        fn name_range<D>(def: D, sema: &Semantics<RootDatabase>) -> Option<FileRange>
+        where
+            D: HasSource,
+            D::Ast: ast::NameOwner,
+        {
+            let src = def.source(sema.db)?;
+            let name = src.value.name()?;
+            let res = src.with_value(name.syntax()).original_file_range(sema.db);
+            Some(res)
+        }
+    }
+}
+
+fn rename_mod(
+    sema: &Semantics<RootDatabase>,
+    module: hir::Module,
+    new_name: &str,
+) -> Result<SourceChange> {
+    if IdentifierKind::classify(new_name)? != IdentifierKind::Ident {
+        bail!("Invalid name `{0}`: cannot rename module to {0}", new_name);
+    }
+
+    let mut source_change = SourceChange::default();
+
+    let InFile { file_id, value: def_source } = module.definition_source(sema.db);
+    let file_id = file_id.original_file(sema.db);
+    if let ModuleSource::SourceFile(..) = def_source {
+        // mod is defined in path/to/dir/mod.rs
+        let path = if module.is_mod_rs(sema.db) {
+            format!("../{}/mod.rs", new_name)
+        } else {
+            format!("{}.rs", new_name)
+        };
+        let dst = AnchoredPathBuf { anchor: file_id, path };
+        let move_file = FileSystemEdit::MoveFile { src: file_id, dst };
+        source_change.push_file_system_edit(move_file);
+    }
+
+    if let Some(InFile { file_id, value: decl_source }) = module.declaration_source(sema.db) {
+        let file_id = file_id.original_file(sema.db);
+        match decl_source.name() {
+            Some(name) => source_change.insert_source_edit(
+                file_id,
+                TextEdit::replace(name.syntax().text_range(), new_name.to_string()),
+            ),
+            _ => never!("Module source node is missing a name"),
+        }
+    }
+    let def = Definition::ModuleDef(hir::ModuleDef::Module(module));
+    let usages = def.usages(sema).all();
+    let ref_edits = usages.iter().map(|(&file_id, references)| {
+        (file_id, source_edit_from_references(references, def, new_name))
+    });
+    source_change.extend(ref_edits);
+
+    Ok(source_change)
+}
+
+fn rename_reference(
+    sema: &Semantics<RootDatabase>,
+    mut def: Definition,
+    new_name: &str,
+) -> Result<SourceChange> {
+    let ident_kind = IdentifierKind::classify(new_name)?;
+
+    if matches!(
+        def, // is target a lifetime?
+        Definition::GenericParam(hir::GenericParam::LifetimeParam(_)) | Definition::Label(_)
+    ) {
+        match ident_kind {
+            IdentifierKind::Ident | IdentifierKind::Underscore => {
+                cov_mark::hit!(rename_not_a_lifetime_ident_ref);
+                bail!("Invalid name `{}`: not a lifetime identifier", new_name);
+            }
+            IdentifierKind::Lifetime => cov_mark::hit!(rename_lifetime),
+        }
+    } else {
+        match (ident_kind, def) {
+            (IdentifierKind::Lifetime, _) => {
+                cov_mark::hit!(rename_not_an_ident_ref);
+                bail!("Invalid name `{}`: not an identifier", new_name);
+            }
+            (IdentifierKind::Ident, _) => cov_mark::hit!(rename_non_local),
+            (IdentifierKind::Underscore, _) => (),
+        }
+    }
+
+    def = match def {
+        // HACK: resolve trait impl items to the item def of the trait definition
+        // so that we properly resolve all trait item references
+        Definition::ModuleDef(mod_def) => mod_def
+            .as_assoc_item(sema.db)
+            .and_then(|it| it.containing_trait_impl(sema.db))
+            .and_then(|it| {
+                it.items(sema.db).into_iter().find_map(|it| match (it, mod_def) {
+                    (hir::AssocItem::Function(trait_func), hir::ModuleDef::Function(func))
+                        if trait_func.name(sema.db) == func.name(sema.db) =>
+                    {
+                        Some(Definition::ModuleDef(hir::ModuleDef::Function(trait_func)))
+                    }
+                    (hir::AssocItem::Const(trait_konst), hir::ModuleDef::Const(konst))
+                        if trait_konst.name(sema.db) == konst.name(sema.db) =>
+                    {
+                        Some(Definition::ModuleDef(hir::ModuleDef::Const(trait_konst)))
+                    }
+                    (
+                        hir::AssocItem::TypeAlias(trait_type_alias),
+                        hir::ModuleDef::TypeAlias(type_alias),
+                    ) if trait_type_alias.name(sema.db) == type_alias.name(sema.db) => {
+                        Some(Definition::ModuleDef(hir::ModuleDef::TypeAlias(trait_type_alias)))
+                    }
+                    _ => None,
+                })
+            })
+            .unwrap_or(def),
+        _ => def,
+    };
+    let usages = def.usages(sema).all();
+
+    if !usages.is_empty() && ident_kind == IdentifierKind::Underscore {
+        cov_mark::hit!(rename_underscore_multiple);
+        bail!("Cannot rename reference to `_` as it is being referenced multiple times");
+    }
+    let mut source_change = SourceChange::default();
+    source_change.extend(usages.iter().map(|(&file_id, references)| {
+        (file_id, source_edit_from_references(references, def, new_name))
+    }));
+
+    let (file_id, edit) = source_edit_from_def(sema, def, new_name)?;
+    source_change.insert_source_edit(file_id, edit);
+    Ok(source_change)
+}
+
+pub fn source_edit_from_references(
+    references: &[FileReference],
+    def: Definition,
+    new_name: &str,
+) -> TextEdit {
+    let mut edit = TextEdit::builder();
+    for reference in references {
+        let (range, replacement) = match &reference.name {
+            // if the ranges differ then the node is inside a macro call, we can't really attempt
+            // to make special rewrites like shorthand syntax and such, so just rename the node in
+            // the macro input
+            ast::NameLike::NameRef(name_ref)
+                if name_ref.syntax().text_range() == reference.range =>
+            {
+                source_edit_from_name_ref(name_ref, new_name, def)
+            }
+            ast::NameLike::Name(name) if name.syntax().text_range() == reference.range => {
+                source_edit_from_name(name, new_name)
+            }
+            _ => None,
+        }
+        .unwrap_or_else(|| (reference.range, new_name.to_string()));
+        edit.replace(range, replacement);
+    }
+    edit.finish()
+}
+
+fn source_edit_from_name(name: &ast::Name, new_name: &str) -> Option<(TextRange, String)> {
+    if let Some(_) = ast::RecordPatField::for_field_name(name) {
+        if let Some(ident_pat) = name.syntax().parent().and_then(ast::IdentPat::cast) {
+            return Some((
+                TextRange::empty(ident_pat.syntax().text_range().start()),
+                [new_name, ": "].concat(),
+            ));
+        }
+    }
+    None
+}
+
+fn source_edit_from_name_ref(
+    name_ref: &ast::NameRef,
+    new_name: &str,
+    def: Definition,
+) -> Option<(TextRange, String)> {
+    if let Some(record_field) = ast::RecordExprField::for_name_ref(name_ref) {
+        let rcf_name_ref = record_field.name_ref();
+        let rcf_expr = record_field.expr();
+        match (rcf_name_ref, rcf_expr.and_then(|it| it.name_ref())) {
+            // field: init-expr, check if we can use a field init shorthand
+            (Some(field_name), Some(init)) => {
+                if field_name == *name_ref {
+                    if init.text() == new_name {
+                        cov_mark::hit!(test_rename_field_put_init_shorthand);
+                        // same names, we can use a shorthand here instead.
+                        // we do not want to erase attributes hence this range start
+                        let s = field_name.syntax().text_range().start();
+                        let e = record_field.syntax().text_range().end();
+                        return Some((TextRange::new(s, e), new_name.to_owned()));
+                    }
+                } else if init == *name_ref {
+                    if field_name.text() == new_name {
+                        cov_mark::hit!(test_rename_local_put_init_shorthand);
+                        // same names, we can use a shorthand here instead.
+                        // we do not want to erase attributes hence this range start
+                        let s = field_name.syntax().text_range().start();
+                        let e = record_field.syntax().text_range().end();
+                        return Some((TextRange::new(s, e), new_name.to_owned()));
+                    }
+                }
+                None
+            }
+            // init shorthand
+            // FIXME: instead of splitting the shorthand, recursively trigger a rename of the
+            // other name https://github.com/rust-analyzer/rust-analyzer/issues/6547
+            (None, Some(_)) if matches!(def, Definition::Field(_)) => {
+                cov_mark::hit!(test_rename_field_in_field_shorthand);
+                let s = name_ref.syntax().text_range().start();
+                Some((TextRange::empty(s), format!("{}: ", new_name)))
+            }
+            (None, Some(_)) if matches!(def, Definition::Local(_)) => {
+                cov_mark::hit!(test_rename_local_in_field_shorthand);
+                let s = name_ref.syntax().text_range().end();
+                Some((TextRange::empty(s), format!(": {}", new_name)))
+            }
+            _ => None,
+        }
+    } else if let Some(record_field) = ast::RecordPatField::for_field_name_ref(name_ref) {
+        let rcf_name_ref = record_field.name_ref();
+        let rcf_pat = record_field.pat();
+        match (rcf_name_ref, rcf_pat) {
+            // field: rename
+            (Some(field_name), Some(ast::Pat::IdentPat(pat))) if field_name == *name_ref => {
+                // field name is being renamed
+                if pat.name().map_or(false, |it| it.text() == new_name) {
+                    cov_mark::hit!(test_rename_field_put_init_shorthand_pat);
+                    // same names, we can use a shorthand here instead/
+                    // we do not want to erase attributes hence this range start
+                    let s = field_name.syntax().text_range().start();
+                    let e = record_field.syntax().text_range().end();
+                    Some((TextRange::new(s, e), pat.to_string()))
+                } else {
+                    None
+                }
+            }
+            _ => None,
+        }
+    } else {
+        None
+    }
+}
+
+fn source_edit_from_def(
+    sema: &Semantics<RootDatabase>,
+    def: Definition,
+    new_name: &str,
+) -> Result<(FileId, TextEdit)> {
+    let frange = def
+        .range_for_rename(sema)
+        .ok_or_else(|| format_err!("No identifier available to rename"))?;
+
+    let mut replacement_text = String::new();
+    let mut repl_range = frange.range;
+    if let Definition::Local(local) = def {
+        if let Either::Left(pat) = local.source(sema.db).value {
+            if matches!(
+                pat.syntax().parent().and_then(ast::RecordPatField::cast),
+                Some(pat_field) if pat_field.name_ref().is_none()
+            ) {
+                replacement_text.push_str(": ");
+                replacement_text.push_str(new_name);
+                repl_range = TextRange::new(
+                    pat.syntax().text_range().end(),
+                    pat.syntax().text_range().end(),
+                );
+            }
+        }
+    }
+    if replacement_text.is_empty() {
+        replacement_text.push_str(new_name);
+    }
+    let edit = TextEdit::replace(repl_range, replacement_text);
+    Ok((frange.file_id, edit))
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub enum IdentifierKind {
+    Ident,
+    Lifetime,
+    Underscore,
+}
+
+impl IdentifierKind {
+    pub fn classify(new_name: &str) -> Result<IdentifierKind> {
+        match lex_single_syntax_kind(new_name) {
+            Some(res) => match res {
+                (SyntaxKind::IDENT, _) => Ok(IdentifierKind::Ident),
+                (T![_], _) => Ok(IdentifierKind::Underscore),
+                (SyntaxKind::LIFETIME_IDENT, _) if new_name != "'static" && new_name != "'_" => {
+                    Ok(IdentifierKind::Lifetime)
+                }
+                (SyntaxKind::LIFETIME_IDENT, _) => {
+                    bail!("Invalid name `{}`: not a lifetime identifier", new_name)
+                }
+                (_, Some(syntax_error)) => bail!("Invalid name `{}`: {}", new_name, syntax_error),
+                (_, None) => bail!("Invalid name `{}`: not an identifier", new_name),
+            },
+            None => bail!("Invalid name `{}`: not an identifier", new_name),
+        }
+    }
+}