27 files changed, 437 insertions, 520 deletions

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index c9ef4b420..6233bca83 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -873,6 +873,10 @@ impl Function {
         db.function_data(self.id).is_unsafe()
     }
 
+    pub fn is_async(self, db: &dyn HirDatabase) -> bool {
+        db.function_data(self.id).is_async()
+    }
+
     pub fn diagnostics(self, db: &dyn HirDatabase, sink: &mut DiagnosticSink) {
         let krate = self.module(db).id.krate();
         hir_def::diagnostics::validate_body(db.upcast(), self.id.into(), sink);
diff --git a/crates/hir_def/src/body.rs b/crates/hir_def/src/body.rs
index 8360426f1..98b485b60 100644
--- a/crates/hir_def/src/body.rs
+++ b/crates/hir_def/src/body.rs
@@ -21,8 +21,6 @@ use profile::Count;
 use rustc_hash::FxHashMap;
 use syntax::{ast, AstNode, AstPtr};
 
-pub use lower::LowerCtx;
-
 use crate::{
     attr::{Attrs, RawAttrs},
     db::DefDatabase,
@@ -35,6 +33,8 @@ use crate::{
     UnresolvedMacro,
 };
 
+pub use lower::LowerCtx;
+
 /// A subset of Expander that only deals with cfg attributes. We only need it to
 /// avoid cyclic queries in crate def map during enum processing.
 #[derive(Debug)]
diff --git a/crates/hir_def/src/find_path.rs b/crates/hir_def/src/find_path.rs
index 858e88038..ee52794aa 100644
--- a/crates/hir_def/src/find_path.rs
+++ b/crates/hir_def/src/find_path.rs
@@ -5,10 +5,10 @@ use std::iter;
 use hir_expand::name::{known, AsName, Name};
 use rustc_hash::FxHashSet;
 
-use crate::nameres::DefMap;
 use crate::{
     db::DefDatabase,
     item_scope::ItemInNs,
+    nameres::DefMap,
     path::{ModPath, PathKind},
     visibility::Visibility,
     ModuleDefId, ModuleId,
@@ -134,7 +134,16 @@ fn find_path_inner(
     for (name, def_id) in root_def_map.extern_prelude() {
         if item == ItemInNs::Types(*def_id) {
             let name = scope_name.unwrap_or_else(|| name.clone());
-            return Some(ModPath::from_segments(PathKind::Plain, vec![name]));
+
+            let name_already_occupied_in_type_ns = def_map
+                .with_ancestor_maps(db, from.local_id, &mut |def_map, local_id| {
+                    def_map[local_id].scope.get(&name).take_types().filter(|&id| id != *def_id)
+                })
+                .is_some();
+            return Some(ModPath::from_segments(
+                if name_already_occupied_in_type_ns { PathKind::Abs } else { PathKind::Plain },
+                vec![name],
+            ));
         }
     }
 
diff --git a/crates/hir_expand/src/builtin_macro.rs b/crates/hir_expand/src/builtin_macro.rs
index af9802144..280c25f11 100644
--- a/crates/hir_expand/src/builtin_macro.rs
+++ b/crates/hir_expand/src/builtin_macro.rs
@@ -118,6 +118,7 @@ register_builtin! {
     EAGER:
     (compile_error, CompileError) => compile_error_expand,
     (concat, Concat) => concat_expand,
+    (concat_idents, ConcatIdents) => concat_idents_expand,
     (include, Include) => include_expand,
     (include_bytes, IncludeBytes) => include_bytes_expand,
     (include_str, IncludeStr) => include_str_expand,
@@ -373,6 +374,28 @@ fn concat_expand(
     ExpandResult { value: Some(ExpandedEager::new(quote!(#text), FragmentKind::Expr)), err }
 }
 
+fn concat_idents_expand(
+    _db: &dyn AstDatabase,
+    _arg_id: EagerMacroId,
+    tt: &tt::Subtree,
+) -> ExpandResult<Option<ExpandedEager>> {
+    let mut err = None;
+    let mut ident = String::new();
+    for (i, t) in tt.token_trees.iter().enumerate() {
+        match t {
+            tt::TokenTree::Leaf(tt::Leaf::Ident(id)) => {
+                ident.push_str(id.text.as_str());
+            }
+            tt::TokenTree::Leaf(tt::Leaf::Punct(punct)) if i % 2 == 1 && punct.char == ',' => (),
+            _ => {
+                err.get_or_insert(mbe::ExpandError::UnexpectedToken);
+            }
+        }
+    }
+    let ident = tt::Ident { text: ident.into(), id: tt::TokenId::unspecified() };
+    ExpandResult { value: Some(ExpandedEager::new(quote!(#ident), FragmentKind::Expr)), err }
+}
+
 fn relative_file(
     db: &dyn AstDatabase,
     call_id: MacroCallId,
@@ -794,4 +817,16 @@ mod tests {
             expect![[r#""foor0bar\nfalse""#]],
         );
     }
+
+    #[test]
+    fn test_concat_idents_expand() {
+        check_expansion(
+            r##"
+            #[rustc_builtin_macro]
+            macro_rules! concat_idents {}
+            concat_idents!(foo, bar);
+            "##,
+            expect![[r#"foobar"#]],
+        );
+    }
 }
diff --git a/crates/hir_expand/src/name.rs b/crates/hir_expand/src/name.rs
index bcfd3e524..5a5dc9afd 100644
--- a/crates/hir_expand/src/name.rs
+++ b/crates/hir_expand/src/name.rs
@@ -212,6 +212,7 @@ pub mod known {
         std_panic,
         stringify,
         concat,
+        concat_idents,
         include,
         include_bytes,
         include_str,
diff --git a/crates/ide/src/doc_links.rs b/crates/ide/src/doc_links.rs
index cb5a8e19a..320694a17 100644
--- a/crates/ide/src/doc_links.rs
+++ b/crates/ide/src/doc_links.rs
@@ -29,7 +29,8 @@ pub(crate) type DocumentationLink = String;
 /// Rewrite documentation links in markdown to point to an online host (e.g. docs.rs)
 pub(crate) fn rewrite_links(db: &RootDatabase, markdown: &str, definition: &Definition) -> String {
     let mut cb = broken_link_clone_cb;
-    let doc = Parser::new_with_broken_link_callback(markdown, Options::empty(), Some(&mut cb));
+    let doc =
+        Parser::new_with_broken_link_callback(markdown, Options::ENABLE_TASKLISTS, Some(&mut cb));
 
     let doc = map_links(doc, |target, title: &str| {
         // This check is imperfect, there's some overlap between valid intra-doc links
@@ -64,8 +65,7 @@ pub(crate) fn rewrite_links(db: &RootDatabase, markdown: &str, definition: &Defi
 pub(crate) fn remove_links(markdown: &str) -> String {
     let mut drop_link = false;
 
-    let mut opts = Options::empty();
-    opts.insert(Options::ENABLE_FOOTNOTES);
+    let opts = Options::ENABLE_TASKLISTS | Options::ENABLE_FOOTNOTES;
 
     let mut cb = |_: BrokenLink| {
         let empty = InlineStr::try_from("").unwrap();
@@ -123,7 +123,7 @@ pub(crate) fn extract_definitions_from_markdown(
 ) -> Vec<(TextRange, String, Option<hir::Namespace>)> {
     Parser::new_with_broken_link_callback(
         markdown,
-        Options::empty(),
+        Options::ENABLE_TASKLISTS,
         Some(&mut broken_link_clone_cb),
     )
     .into_offset_iter()
diff --git a/crates/ide/src/syntax_highlighting/highlight.rs b/crates/ide/src/syntax_highlighting/highlight.rs
index b586dcc17..baed8e217 100644
--- a/crates/ide/src/syntax_highlighting/highlight.rs
+++ b/crates/ide/src/syntax_highlighting/highlight.rs
@@ -227,8 +227,8 @@ pub(super) fn element(
         k if k.is_keyword() => {
             let h = Highlight::new(HlTag::Keyword);
             match k {
-                T![await]
-                | T![break]
+                T![await] => h | HlMod::Async | HlMod::ControlFlow,
+                T![break]
                 | T![continue]
                 | T![else]
                 | T![if]
@@ -255,6 +255,7 @@ pub(super) fn element(
                     })
                     .map(|modifier| h | modifier)
                     .unwrap_or(h),
+                T![async] => h | HlMod::Async,
                 _ => h,
             }
         }
@@ -310,6 +311,9 @@ fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
                 if func.is_unsafe(db) {
                     h |= HlMod::Unsafe;
                 }
+                if func.is_async(db) {
+                    h |= HlMod::Async;
+                }
                 return h;
             }
             hir::ModuleDef::Adt(hir::Adt::Struct(_)) => HlTag::Symbol(SymbolKind::Struct),
@@ -409,6 +413,9 @@ fn highlight_method_call(
     if func.is_unsafe(sema.db) || sema.is_unsafe_method_call(&method_call) {
         h |= HlMod::Unsafe;
     }
+    if func.is_async(sema.db) {
+        h |= HlMod::Async;
+    }
     if func.as_assoc_item(sema.db).and_then(|it| it.containing_trait(sema.db)).is_some() {
         h |= HlMod::Trait
     }
diff --git a/crates/ide/src/syntax_highlighting/tags.rs b/crates/ide/src/syntax_highlighting/tags.rs
index a304b3250..f4a2e7506 100644
--- a/crates/ide/src/syntax_highlighting/tags.rs
+++ b/crates/ide/src/syntax_highlighting/tags.rs
@@ -65,6 +65,8 @@ pub enum HlMod {
     Static,
     /// Used for items in traits and trait impls.
     Trait,
+    /// Used with keywords like `async` and `await`.
+    Async,
     // Keep this last!
     /// Used for unsafe functions, mutable statics, union accesses and unsafe operations.
     Unsafe,
@@ -186,6 +188,7 @@ impl HlMod {
         HlMod::Mutable,
         HlMod::Static,
         HlMod::Trait,
+        HlMod::Async,
         HlMod::Unsafe,
     ];
 
@@ -203,6 +206,7 @@ impl HlMod {
             HlMod::Mutable => "mutable",
             HlMod::Static => "static",
             HlMod::Trait => "trait",
+            HlMod::Async => "async",
             HlMod::Unsafe => "unsafe",
         }
     }
diff --git a/crates/ide/src/syntax_highlighting/test_data/highlighting.html b/crates/ide/src/syntax_highlighting/test_data/highlighting.html
index df4192194..33bc6b0f3 100644
--- a/crates/ide/src/syntax_highlighting/test_data/highlighting.html
+++ b/crates/ide/src/syntax_highlighting/test_data/highlighting.html
@@ -234,4 +234,15 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
             <span class="variable declaration">Nope</span> <span class="operator">=&gt;</span> <span class="variable">Nope</span><span class="comma">,</span>
         <span class="brace">}</span>
     <span class="brace">}</span>
+<span class="brace">}</span>
+
+<span class="keyword async">async</span> <span class="keyword">fn</span> <span class="function declaration async">learn_and_sing</span><span class="parenthesis">(</span><span class="parenthesis">)</span> <span class="brace">{</span>
+    <span class="keyword">let</span> <span class="variable declaration">song</span> <span class="operator">=</span> <span class="unresolved_reference">learn_song</span><span class="parenthesis">(</span><span class="parenthesis">)</span><span class="operator">.</span><span class="keyword control async">await</span><span class="semicolon">;</span>
+    <span class="unresolved_reference">sing_song</span><span class="parenthesis">(</span><span class="variable consuming">song</span><span class="parenthesis">)</span><span class="operator">.</span><span class="keyword control async">await</span><span class="semicolon">;</span>
+<span class="brace">}</span>
+
+<span class="keyword async">async</span> <span class="keyword">fn</span> <span class="function declaration async">async_main</span><span class="parenthesis">(</span><span class="parenthesis">)</span> <span class="brace">{</span>
+    <span class="keyword">let</span> <span class="variable declaration">f1</span> <span class="operator">=</span> <span class="function async">learn_and_sing</span><span class="parenthesis">(</span><span class="parenthesis">)</span><span class="semicolon">;</span>
+    <span class="keyword">let</span> <span class="variable declaration">f2</span> <span class="operator">=</span> <span class="unresolved_reference">dance</span><span class="parenthesis">(</span><span class="parenthesis">)</span><span class="semicolon">;</span>
+    futures::<span class="macro">join!</span><span class="parenthesis">(</span>f1<span class="comma">,</span> f2<span class="parenthesis">)</span><span class="semicolon">;</span>
 <span class="brace">}</span></code></pre>
\ No newline at end of file
diff --git a/crates/ide/src/syntax_highlighting/tests.rs b/crates/ide/src/syntax_highlighting/tests.rs
index b6e952b08..32f2d9038 100644
--- a/crates/ide/src/syntax_highlighting/tests.rs
+++ b/crates/ide/src/syntax_highlighting/tests.rs
@@ -208,6 +208,17 @@ impl<T> Option<T> {
         }
     }
 }
+
+async fn learn_and_sing() {
+    let song = learn_song().await;
+    sing_song(song).await;
+}
+
+async fn async_main() {
+    let f1 = learn_and_sing();
+    let f2 = dance();
+    futures::join!(f1, f2);
+}
 "#
         .trim(),
         expect_file!["./test_data/highlighting.html"],
diff --git a/crates/ide_assists/src/handlers/add_missing_impl_members.rs b/crates/ide_assists/src/handlers/add_missing_impl_members.rs
index 0148635f9..8225ae22c 100644
--- a/crates/ide_assists/src/handlers/add_missing_impl_members.rs
+++ b/crates/ide_assists/src/handlers/add_missing_impl_members.rs
@@ -64,7 +64,6 @@ pub(crate) fn add_missing_impl_members(acc: &mut Assists, ctx: &AssistContext) -
 // impl Trait for () {
 //     type X = ();
 //     fn foo(&self) {}$0
-//
 // }
 // ```
 // ->
@@ -195,6 +194,7 @@ impl Foo for S {
     fn baz(&self) {
         todo!()
     }
+
 }"#,
         );
     }
@@ -231,6 +231,7 @@ impl Foo for S {
     fn foo(&self) {
         ${0:todo!()}
     }
+
 }"#,
         );
     }
diff --git a/crates/ide_assists/src/handlers/auto_import.rs b/crates/ide_assists/src/handlers/auto_import.rs
index a454a2af3..506cc292c 100644
--- a/crates/ide_assists/src/handlers/auto_import.rs
+++ b/crates/ide_assists/src/handlers/auto_import.rs
@@ -969,4 +969,30 @@ mod bar {
 "#,
         );
     }
+
+    #[test]
+    fn uses_abs_path_with_extern_crate_clash() {
+        check_assist(
+            auto_import,
+            r#"
+//- /main.rs crate:main deps:foo
+mod foo {}
+
+const _: () = {
+    Foo$0
+};
+//- /foo.rs crate:foo
+pub struct Foo
+"#,
+            r#"
+use ::foo::Foo;
+
+mod foo {}
+
+const _: () = {
+    Foo
+};
+"#,
+        );
+    }
 }
diff --git a/crates/ide_assists/src/handlers/generate_new.rs b/crates/ide_assists/src/handlers/generate_new.rs
index 8ce5930b7..959a1f86c 100644
--- a/crates/ide_assists/src/handlers/generate_new.rs
+++ b/crates/ide_assists/src/handlers/generate_new.rs
@@ -1,4 +1,3 @@
-use ast::Adt;
 use itertools::Itertools;
 use stdx::format_to;
 use syntax::ast::{self, AstNode, NameOwner, StructKind, VisibilityOwner};
@@ -37,7 +36,7 @@ pub(crate) fn generate_new(acc: &mut Assists, ctx: &AssistContext) -> Option<()>
     };
 
     // Return early if we've found an existing new fn
-    let impl_def = find_struct_impl(&ctx, &Adt::Struct(strukt.clone()), "new")?;
+    let impl_def = find_struct_impl(&ctx, &ast::Adt::Struct(strukt.clone()), "new")?;
 
     let target = strukt.syntax().text_range();
     acc.add(AssistId("generate_new", AssistKind::Generate), "Generate `new`", target, |builder| {
@@ -60,7 +59,7 @@ pub(crate) fn generate_new(acc: &mut Assists, ctx: &AssistContext) -> Option<()>
         let start_offset = impl_def
             .and_then(|impl_def| find_impl_block_start(impl_def, &mut buf))
             .unwrap_or_else(|| {
-                buf = generate_impl_text(&Adt::Struct(strukt.clone()), &buf);
+                buf = generate_impl_text(&ast::Adt::Struct(strukt.clone()), &buf);
                 strukt.syntax().text_range().end()
             });
 
@@ -81,101 +80,132 @@ mod tests {
     use super::*;
 
     #[test]
-    #[rustfmt::skip]
     fn test_generate_new() {
-        // Check output of generation
         check_assist(
             generate_new,
-"struct Foo {$0}",
-"struct Foo {}
+            r#"
+struct Foo {$0}
+"#,
+            r#"
+struct Foo {}
 
 impl Foo {
     fn $0new() -> Self { Self {  } }
-}",
+}
+"#,
         );
         check_assist(
             generate_new,
-"struct Foo<T: Clone> {$0}",
-"struct Foo<T: Clone> {}
+            r#"
+struct Foo<T: Clone> {$0}
+"#,
+            r#"
+struct Foo<T: Clone> {}
 
 impl<T: Clone> Foo<T> {
     fn $0new() -> Self { Self {  } }
-}",
+}
+"#,
         );
         check_assist(
             generate_new,
-"struct Foo<'a, T: Foo<'a>> {$0}",
-"struct Foo<'a, T: Foo<'a>> {}
+            r#"
+struct Foo<'a, T: Foo<'a>> {$0}
+"#,
+            r#"
+struct Foo<'a, T: Foo<'a>> {}
 
 impl<'a, T: Foo<'a>> Foo<'a, T> {
     fn $0new() -> Self { Self {  } }
-}",
+}
+"#,
         );
         check_assist(
             generate_new,
-"struct Foo { baz: String $0}",
-"struct Foo { baz: String }
+            r#"
+struct Foo { baz: String $0}
+"#,
+            r#"
+struct Foo { baz: String }
 
 impl Foo {
     fn $0new(baz: String) -> Self { Self { baz } }
-}",
+}
+"#,
         );
         check_assist(
             generate_new,
-"struct Foo { baz: String, qux: Vec<i32> $0}",
-"struct Foo { baz: String, qux: Vec<i32> }
+            r#"
+struct Foo { baz: String, qux: Vec<i32> $0}
+"#,
+            r#"
+struct Foo { baz: String, qux: Vec<i32> }
 
 impl Foo {
     fn $0new(baz: String, qux: Vec<i32>) -> Self { Self { baz, qux } }
-}",
+}
+"#,
         );
+    }
 
-        // Check that visibility modifiers don't get brought in for fields
+    #[test]
+    fn check_that_visibility_modifiers_dont_get_brought_in() {
         check_assist(
             generate_new,
-"struct Foo { pub baz: String, pub qux: Vec<i32> $0}",
-"struct Foo { pub baz: String, pub qux: Vec<i32> }
+            r#"
+struct Foo { pub baz: String, pub qux: Vec<i32> $0}
+"#,
+            r#"
+struct Foo { pub baz: String, pub qux: Vec<i32> }
 
 impl Foo {
     fn $0new(baz: String, qux: Vec<i32>) -> Self { Self { baz, qux } }
-}",
+}
+"#,
         );
+    }
 
-        // Check that it reuses existing impls
+    #[test]
+    fn check_it_reuses_existing_impls() {
         check_assist(
             generate_new,
-"struct Foo {$0}
+            r#"
+struct Foo {$0}
 
 impl Foo {}
-",
-"struct Foo {}
+"#,
+            r#"
+struct Foo {}
 
 impl Foo {
     fn $0new() -> Self { Self {  } }
 }
-",
+"#,
         );
         check_assist(
             generate_new,
-"struct Foo {$0}
+            r#"
+struct Foo {$0}
 
 impl Foo {
     fn qux(&self) {}
 }
-",
-"struct Foo {}
+"#,
+            r#"
+struct Foo {}
 
 impl Foo {
     fn $0new() -> Self { Self {  } }
 
     fn qux(&self) {}
 }
-",
+"#,
         );
 
         check_assist(
             generate_new,
-"struct Foo {$0}
+            r#"
+struct Foo {$0}
 
 impl Foo {
     fn qux(&self) {}
@@ -183,8 +213,9 @@ impl Foo {
         5
     }
 }
-",
-"struct Foo {}
+"#,
+            r#"
+struct Foo {}
 
 impl Foo {
     fn $0new() -> Self { Self {  } }
@@ -194,27 +225,37 @@ impl Foo {
         5
     }
 }
-",
+"#,
         );
+    }
 
-        // Check visibility of new fn based on struct
+    #[test]
+    fn check_visibility_of_new_fn_based_on_struct() {
         check_assist(
             generate_new,
-"pub struct Foo {$0}",
-"pub struct Foo {}
+            r#"
+pub struct Foo {$0}
+"#,
+            r#"
+pub struct Foo {}
 
 impl Foo {
     pub fn $0new() -> Self { Self {  } }
-}",
+}
+"#,
         );
         check_assist(
             generate_new,
-"pub(crate) struct Foo {$0}",
-"pub(crate) struct Foo {}
+            r#"
+pub(crate) struct Foo {$0}
+"#,
+            r#"
+pub(crate) struct Foo {}
 
 impl Foo {
     pub(crate) fn $0new() -> Self { Self {  } }
-}",
+}
+"#,
         );
     }
 
@@ -222,26 +263,28 @@ impl Foo {
     fn generate_new_not_applicable_if_fn_exists() {
         check_assist_not_applicable(
             generate_new,
-            "
+            r#"
 struct Foo {$0}
 
 impl Foo {
     fn new() -> Self {
         Self
     }
-}",
+}
+"#,
         );
 
         check_assist_not_applicable(
             generate_new,
-            "
+            r#"
 struct Foo {$0}
 
 impl Foo {
     fn New() -> Self {
         Self
     }
-}",
+}
+"#,
         );
     }
 
@@ -249,12 +292,12 @@ impl Foo {
     fn generate_new_target() {
         check_assist_target(
             generate_new,
-            "
+            r#"
 struct SomeThingIrrelevant;
 /// Has a lifetime parameter
 struct Foo<'a, T: Foo<'a>> {$0}
 struct EvenMoreIrrelevant;
-",
+"#,
             "/// Has a lifetime parameter
 struct Foo<'a, T: Foo<'a>> {}",
         );
@@ -264,7 +307,7 @@ struct Foo<'a, T: Foo<'a>> {}",
     fn test_unrelated_new() {
         check_assist(
             generate_new,
-            r##"
+            r#"
 pub struct AstId<N: AstNode> {
     file_id: HirFileId,
     file_ast_id: FileAstId<N>,
@@ -285,8 +328,9 @@ impl<T> Source<T> {
     pub fn map<F: FnOnce(T) -> U, U>(self, f: F) -> Source<U> {
         Source { file_id: self.file_id, ast: f(self.ast) }
     }
-}"##,
-            r##"
+}
+"#,
+            r#"
 pub struct AstId<N: AstNode> {
     file_id: HirFileId,
     file_ast_id: FileAstId<N>,
@@ -309,7 +353,8 @@ impl<T> Source<T> {
     pub fn map<F: FnOnce(T) -> U, U>(self, f: F) -> Source<U> {
         Source { file_id: self.file_id, ast: f(self.ast) }
     }
-}"##,
+}
+"#,
         );
     }
 }
diff --git a/crates/ide_assists/src/handlers/move_module_to_file.rs b/crates/ide_assists/src/handlers/move_module_to_file.rs
index 6e685b4b2..93f702c55 100644
--- a/crates/ide_assists/src/handlers/move_module_to_file.rs
+++ b/crates/ide_assists/src/handlers/move_module_to_file.rs
@@ -1,4 +1,4 @@
-use ast::{edit::IndentLevel, VisibilityOwner};
+use ast::edit::IndentLevel;
 use ide_db::base_db::AnchoredPathBuf;
 use stdx::format_to;
 use syntax::{
@@ -60,12 +60,18 @@ pub(crate) fn move_module_to_file(acc: &mut Assists, ctx: &AssistContext) -> Opt
             };
 
             let mut buf = String::new();
-            if let Some(v) = module_ast.visibility() {
-                format_to!(buf, "{} ", v);
-            }
             format_to!(buf, "mod {};", module_name);
 
-            builder.replace(module_ast.syntax().text_range(), buf);
+            let replacement_start = if let Some(mod_token) = module_ast.mod_token() {
+                mod_token.text_range().start()
+            } else {
+                module_ast.syntax().text_range().start()
+            };
+
+            builder.replace(
+                TextRange::new(replacement_start, module_ast.syntax().text_range().end()),
+                buf,
+            );
 
             let dst = AnchoredPathBuf { anchor: ctx.frange.file_id, path };
             builder.create_file(dst, contents);
@@ -184,4 +190,26 @@ pub(crate) mod tests;
         cov_mark::check!(available_before_curly);
         check_assist_not_applicable(move_module_to_file, r#"mod m { $0 }"#);
     }
+
+    #[test]
+    fn keep_outer_comments_and_attributes() {
+        check_assist(
+            move_module_to_file,
+            r#"
+/// doc comment
+#[attribute]
+mod $0tests {
+    #[test] fn t() {}
+}
+"#,
+            r#"
+//- /main.rs
+/// doc comment
+#[attribute]
+mod tests;
+//- /tests.rs
+#[test] fn t() {}
+"#,
+        );
+    }
 }
diff --git a/crates/ide_assists/src/handlers/replace_unwrap_with_match.rs b/crates/ide_assists/src/handlers/replace_unwrap_with_match.rs
index 0fec961b4..a3bfa221c 100644
--- a/crates/ide_assists/src/handlers/replace_unwrap_with_match.rs
+++ b/crates/ide_assists/src/handlers/replace_unwrap_with_match.rs
@@ -17,7 +17,7 @@ use ide_db::ty_filter::TryEnum;
 
 // Assist: replace_unwrap_with_match
 //
-// Replaces `unwrap` a `match` expression. Works for Result and Option.
+// Replaces `unwrap` with a `match` expression. Works for Result and Option.
 //
 // ```
 // enum Result<T, E> { Ok(T), Err(E) }
diff --git a/crates/ide_assists/src/tests/generated.rs b/crates/ide_assists/src/tests/generated.rs
index 49c1a9776..4406406a2 100644
--- a/crates/ide_assists/src/tests/generated.rs
+++ b/crates/ide_assists/src/tests/generated.rs
@@ -50,7 +50,6 @@ trait Trait {
 impl Trait for () {
     type X = ();
     fn foo(&self) {}$0
-
 }
 "#####,
         r#####"
diff --git a/crates/ide_assists/src/utils.rs b/crates/ide_assists/src/utils.rs
index 0dcf20c61..fc7caee04 100644
--- a/crates/ide_assists/src/utils.rs
+++ b/crates/ide_assists/src/utils.rs
@@ -17,7 +17,7 @@ use syntax::{
     ast::AttrsOwner,
     ast::NameOwner,
     ast::{self, edit, make, ArgListOwner, GenericParamsOwner},
-    AstNode, Direction, SmolStr,
+    ted, AstNode, Direction, SmolStr,
     SyntaxKind::*,
     SyntaxNode, TextSize, T,
 };
@@ -128,43 +128,43 @@ pub fn add_trait_assoc_items_to_impl(
     sema: &hir::Semantics<ide_db::RootDatabase>,
     items: Vec<ast::AssocItem>,
     trait_: hir::Trait,
-    impl_def: ast::Impl,
+    impl_: ast::Impl,
     target_scope: hir::SemanticsScope,
 ) -> (ast::Impl, ast::AssocItem) {
-    let impl_item_list = impl_def.assoc_item_list().unwrap_or_else(make::assoc_item_list);
-
-    let n_existing_items = impl_item_list.assoc_items().count();
     let source_scope = sema.scope_for_def(trait_);
     let ast_transform = QualifyPaths::new(&target_scope, &source_scope)
-        .or(SubstituteTypeParams::for_trait_impl(&source_scope, trait_, impl_def.clone()));
+        .or(SubstituteTypeParams::for_trait_impl(&source_scope, trait_, impl_.clone()));
 
     let items = items
         .into_iter()
         .map(|it| it.clone_for_update())
         .inspect(|it| ast_transform::apply(&*ast_transform, it))
-        .map(|it| match it {
-            ast::AssocItem::Fn(def) => ast::AssocItem::Fn(add_body(def)),
-            ast::AssocItem::TypeAlias(def) => ast::AssocItem::TypeAlias(def.remove_bounds()),
-            _ => it,
-        })
-        .map(|it| edit::remove_attrs_and_docs(&it));
-
-    let new_impl_item_list = impl_item_list.append_items(items);
-    let new_impl_def = impl_def.with_assoc_item_list(new_impl_item_list);
-    let first_new_item =
-        new_impl_def.assoc_item_list().unwrap().assoc_items().nth(n_existing_items).unwrap();
-    return (new_impl_def, first_new_item);
-
-    fn add_body(fn_def: ast::Fn) -> ast::Fn {
-        match fn_def.body() {
-            Some(_) => fn_def,
-            None => {
+        .map(|it| edit::remove_attrs_and_docs(&it).clone_subtree().clone_for_update());
+
+    let res = impl_.clone_for_update();
+
+    let assoc_item_list = res.get_or_create_assoc_item_list();
+    let mut first_item = None;
+    for item in items {
+        first_item.get_or_insert_with(|| item.clone());
+        match &item {
+            ast::AssocItem::Fn(fn_) if fn_.body().is_none() => {
                 let body = make::block_expr(None, Some(make::ext::expr_todo()))
                     .indent(edit::IndentLevel(1));
-                fn_def.with_body(body)
+                ted::replace(fn_.get_or_create_body().syntax(), body.clone_for_update().syntax())
             }
+            ast::AssocItem::TypeAlias(type_alias) => {
+                if let Some(type_bound_list) = type_alias.type_bound_list() {
+                    type_bound_list.remove()
+                }
+            }
+            _ => {}
         }
+
+        assoc_item_list.add_item(item)
     }
+
+    (res, first_item.unwrap())
 }
 
 #[derive(Clone, Copy, Debug)]
diff --git a/crates/ide_db/src/helpers/merge_imports.rs b/crates/ide_db/src/helpers/merge_imports.rs
index af2a51a4d..8fb40e837 100644
--- a/crates/ide_db/src/helpers/merge_imports.rs
+++ b/crates/ide_db/src/helpers/merge_imports.rs
@@ -2,8 +2,9 @@
 use std::cmp::Ordering;
 
 use itertools::{EitherOrBoth, Itertools};
-use syntax::ast::{
-    self, edit::AstNodeEdit, make, AstNode, AttrsOwner, PathSegmentKind, VisibilityOwner,
+use syntax::{
+    ast::{self, make, AstNode, AttrsOwner, PathSegmentKind, VisibilityOwner},
+    ted,
 };
 
 /// What type of merges are allowed.
@@ -41,10 +42,12 @@ pub fn try_merge_imports(
         return None;
     }
 
+    let lhs = lhs.clone_subtree().clone_for_update();
     let lhs_tree = lhs.use_tree()?;
     let rhs_tree = rhs.use_tree()?;
     let merged = try_merge_trees(&lhs_tree, &rhs_tree, merge_behavior)?;
-    Some(lhs.with_use_tree(merged).clone_for_update())
+    ted::replace(lhs_tree.syntax(), merged.syntax());
+    Some(lhs)
 }
 
 pub fn try_merge_trees(
@@ -65,7 +68,7 @@ pub fn try_merge_trees(
     } else {
         (lhs.split_prefix(&lhs_prefix), rhs.split_prefix(&rhs_prefix))
     };
-    recursive_merge(&lhs, &rhs, merge)
+    recursive_merge(&lhs, &rhs, merge).map(|it| it.clone_for_update())
 }
 
 /// Recursively "zips" together lhs and rhs.
@@ -78,7 +81,8 @@ fn recursive_merge(
         .use_tree_list()
         .into_iter()
         .flat_map(|list| list.use_trees())
-        // we use Option here to early return from this function(this is not the same as a `filter` op)
+        // We use Option here to early return from this function(this is not the
+        // same as a `filter` op).
         .map(|tree| match merge.is_tree_allowed(&tree) {
             true => Some(tree),
             false => None,
@@ -111,8 +115,10 @@ fn recursive_merge(
                     let tree_is_self = |tree: ast::UseTree| {
                         tree.path().as_ref().map(path_is_self).unwrap_or(false)
                     };
-                    // check if only one of the two trees has a tree list, and whether that then contains `self` or not.
-                    // If this is the case we can skip this iteration since the path without the list is already included in the other one via `self`
+                    // Check if only one of the two trees has a tree list, and
+                    // whether that then contains `self` or not. If this is the
+                    // case we can skip this iteration since the path without
+                    // the list is already included in the other one via `self`.
                     let tree_contains_self = |tree: &ast::UseTree| {
                         tree.use_tree_list()
                             .map(|tree_list| tree_list.use_trees().any(tree_is_self))
@@ -127,9 +133,11 @@ fn recursive_merge(
                         _ => (),
                     }
 
-                    // glob imports arent part of the use-tree lists so we need to special handle them here as well
-                    // this special handling is only required for when we merge a module import into a glob import of said module
-                    // see the `merge_self_glob` or `merge_mod_into_glob` tests
+                    // Glob imports aren't part of the use-tree lists so we need
+                    // to special handle them here as well this special handling
+                    // is only required for when we merge a module import into a
+                    // glob import of said module see the `merge_self_glob` or
+                    // `merge_mod_into_glob` tests.
                     if lhs_t.star_token().is_some() || rhs_t.star_token().is_some() {
                         *lhs_t = make::use_tree(
                             make::path_unqualified(make::path_segment_self()),
@@ -165,11 +173,11 @@ fn recursive_merge(
         }
     }
 
-    Some(if let Some(old) = lhs.use_tree_list() {
-        lhs.replace_descendant(old, make::use_tree_list(use_trees)).clone_for_update()
-    } else {
-        lhs.clone()
-    })
+    let lhs = lhs.clone_subtree().clone_for_update();
+    if let Some(old) = lhs.use_tree_list() {
+        ted::replace(old.syntax(), make::use_tree_list(use_trees).syntax().clone_for_update());
+    }
+    ast::UseTree::cast(lhs.syntax().clone_subtree())
 }
 
 /// Traverses both paths until they differ, returning the common prefix of both.
diff --git a/crates/rust-analyzer/src/semantic_tokens.rs b/crates/rust-analyzer/src/semantic_tokens.rs
index ecab89b2a..c9d38693e 100644
--- a/crates/rust-analyzer/src/semantic_tokens.rs
+++ b/crates/rust-analyzer/src/semantic_tokens.rs
@@ -91,6 +91,7 @@ define_semantic_token_modifiers![
     (INJECTED, "injected"),
     (MUTABLE, "mutable"),
     (CONSUMING, "consuming"),
+    (ASYNC, "async"),
     (UNSAFE, "unsafe"),
     (ATTRIBUTE_MODIFIER, "attribute"),
     (TRAIT_MODIFIER, "trait"),
diff --git a/crates/rust-analyzer/src/to_proto.rs b/crates/rust-analyzer/src/to_proto.rs
index ecf6fd12f..8ce4aa242 100644
--- a/crates/rust-analyzer/src/to_proto.rs
+++ b/crates/rust-analyzer/src/to_proto.rs
@@ -496,6 +496,7 @@ fn semantic_token_type_and_modifiers(
             HlMod::ControlFlow => semantic_tokens::CONTROL_FLOW,
             HlMod::Mutable => semantic_tokens::MUTABLE,
             HlMod::Consuming => semantic_tokens::CONSUMING,
+            HlMod::Async => semantic_tokens::ASYNC,
             HlMod::Unsafe => semantic_tokens::UNSAFE,
             HlMod::Callable => semantic_tokens::CALLABLE,
             HlMod::Static => lsp_types::SemanticTokenModifier::STATIC,
diff --git a/crates/syntax/Cargo.toml b/crates/syntax/Cargo.toml
index c0bc59918..747f0b9eb 100644
--- a/crates/syntax/Cargo.toml
+++ b/crates/syntax/Cargo.toml
@@ -13,7 +13,7 @@ doctest = false
 [dependencies]
 cov-mark = { version = "1.1", features = ["thread-local"] }
 itertools = "0.10.0"
-rowan = "=0.13.0-pre.5"
+rowan = "=0.13.0-pre.6"
 rustc_lexer = { version = "716.0.0", package = "rustc-ap-rustc_lexer" }
 rustc-hash = "1.1.0"
 arrayvec = "0.7"
diff --git a/crates/syntax/src/algo.rs b/crates/syntax/src/algo.rs
index 3f9b84ab9..241713c48 100644
--- a/crates/syntax/src/algo.rs
+++ b/crates/syntax/src/algo.rs
@@ -1,6 +1,6 @@
 //! FIXME: write short doc here
 
-use std::{fmt, hash::BuildHasherDefault, ops::RangeInclusive};
+use std::{hash::BuildHasherDefault, ops::RangeInclusive};
 
 use indexmap::IndexMap;
 use itertools::Itertools;
@@ -330,137 +330,6 @@ fn _replace_children(
     with_children(parent, new_children)
 }
 
-#[derive(Debug, PartialEq, Eq, Hash)]
-enum InsertPos {
-    FirstChildOf(SyntaxNode),
-    After(SyntaxElement),
-}
-
-#[derive(Default)]
-pub struct SyntaxRewriter<'a> {
-    //FIXME: add debug_assertions that all elements are in fact from the same file.
-    replacements: FxHashMap<SyntaxElement, Replacement>,
-    insertions: IndexMap<InsertPos, Vec<SyntaxElement>>,
-    _pd: std::marker::PhantomData<&'a ()>,
-}
-
-impl fmt::Debug for SyntaxRewriter<'_> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("SyntaxRewriter")
-            .field("replacements", &self.replacements)
-            .field("insertions", &self.insertions)
-            .finish()
-    }
-}
-
-impl SyntaxRewriter<'_> {
-    pub fn replace<T: Clone + Into<SyntaxElement>>(&mut self, what: &T, with: &T) {
-        let what = what.clone().into();
-        let replacement = Replacement::Single(with.clone().into());
-        self.replacements.insert(what, replacement);
-    }
-
-    pub fn rewrite(&self, node: &SyntaxNode) -> SyntaxNode {
-        let _p = profile::span("rewrite");
-
-        if self.replacements.is_empty() && self.insertions.is_empty() {
-            return node.clone();
-        }
-        let green = self.rewrite_children(node);
-        with_green(node, green)
-    }
-
-    pub fn rewrite_ast<N: AstNode>(self, node: &N) -> N {
-        N::cast(self.rewrite(node.syntax())).unwrap()
-    }
-
-    /// Returns a node that encompasses all replacements to be done by this rewriter.
-    ///
-    /// Passing the returned node to `rewrite` will apply all replacements queued up in `self`.
-    ///
-    /// Returns `None` when there are no replacements.
-    pub fn rewrite_root(&self) -> Option<SyntaxNode> {
-        let _p = profile::span("rewrite_root");
-        fn element_to_node_or_parent(element: &SyntaxElement) -> Option<SyntaxNode> {
-            match element {
-                SyntaxElement::Node(it) => Some(it.clone()),
-                SyntaxElement::Token(it) => it.parent(),
-            }
-        }
-
-        self.replacements
-            .keys()
-            .filter_map(element_to_node_or_parent)
-            .chain(self.insertions.keys().filter_map(|pos| match pos {
-                InsertPos::FirstChildOf(it) => Some(it.clone()),
-                InsertPos::After(it) => element_to_node_or_parent(it),
-            }))
-            // If we only have one replacement/insertion, we must return its parent node, since `rewrite` does
-            // not replace the node passed to it.
-            .map(|it| it.parent().unwrap_or(it))
-            .fold1(|a, b| least_common_ancestor(&a, &b).unwrap())
-    }
-
-    fn replacement(&self, element: &SyntaxElement) -> Option<Replacement> {
-        self.replacements.get(element).cloned()
-    }
-
-    fn insertions(&self, pos: &InsertPos) -> Option<impl Iterator<Item = SyntaxElement> + '_> {
-        self.insertions.get(pos).map(|insertions| insertions.iter().cloned())
-    }
-
-    fn rewrite_children(&self, node: &SyntaxNode) -> rowan::GreenNode {
-        let _p = profile::span("rewrite_children");
-
-        //  FIXME: this could be made much faster.
-        let mut new_children = Vec::new();
-        if let Some(elements) = self.insertions(&InsertPos::FirstChildOf(node.clone())) {
-            new_children.extend(elements.map(element_to_green));
-        }
-        for child in node.children_with_tokens() {
-            self.rewrite_self(&mut new_children, &child);
-        }
-
-        rowan::GreenNode::new(rowan::SyntaxKind(node.kind() as u16), new_children)
-    }
-
-    fn rewrite_self(
-        &self,
-        acc: &mut Vec<NodeOrToken<rowan::GreenNode, rowan::GreenToken>>,
-        element: &SyntaxElement,
-    ) {
-        let _p = profile::span("rewrite_self");
-
-        if let Some(replacement) = self.replacement(&element) {
-            match replacement {
-                Replacement::Single(element) => acc.push(element_to_green(element)),
-            };
-        } else {
-            match element {
-                NodeOrToken::Token(it) => acc.push(NodeOrToken::Token(it.green().to_owned())),
-                NodeOrToken::Node(it) => {
-                    acc.push(NodeOrToken::Node(self.rewrite_children(it)));
-                }
-            }
-        }
-        if let Some(elements) = self.insertions(&InsertPos::After(element.clone())) {
-            acc.extend(elements.map(element_to_green));
-        }
-    }
-}
-
-fn element_to_green(element: SyntaxElement) -> NodeOrToken<rowan::GreenNode, rowan::GreenToken> {
-    match element {
-        NodeOrToken::Node(it) => NodeOrToken::Node(it.green().into_owned()),
-        NodeOrToken::Token(it) => NodeOrToken::Token(it.green().to_owned()),
-    }
-}
-
-#[derive(Clone, Debug)]
-enum Replacement {
-    Single(SyntaxElement),
-}
-
 fn with_children(
     parent: &SyntaxNode,
     new_children: Vec<NodeOrToken<rowan::GreenNode, rowan::GreenToken>>,
diff --git a/crates/syntax/src/ast.rs b/crates/syntax/src/ast.rs
index 7f472d4db..a8071b51d 100644
--- a/crates/syntax/src/ast.rs
+++ b/crates/syntax/src/ast.rs
@@ -47,6 +47,12 @@ pub trait AstNode {
     {
         Self::cast(self.syntax().clone_for_update()).unwrap()
     }
+    fn clone_subtree(&self) -> Self
+    where
+        Self: Sized,
+    {
+        Self::cast(self.syntax().clone_subtree()).unwrap()
+    }
 }
 
 /// Like `AstNode`, but wraps tokens rather than interior nodes.
diff --git a/crates/syntax/src/ast/edit.rs b/crates/syntax/src/ast/edit.rs
index cbc75f922..4b5f5c571 100644
--- a/crates/syntax/src/ast/edit.rs
+++ b/crates/syntax/src/ast/edit.rs
@@ -2,20 +2,20 @@
 //! immutable, all function here return a fresh copy of the tree, instead of
 //! doing an in-place modification.
 use std::{
-    array, fmt, iter,
+    fmt, iter,
     ops::{self, RangeInclusive},
 };
 
 use arrayvec::ArrayVec;
 
 use crate::{
-    algo::{self, SyntaxRewriter},
+    algo,
     ast::{
         self,
         make::{self, tokens},
-        AstNode, GenericParamsOwner, NameOwner, TypeBoundsOwner,
+        AstNode,
     },
-    AstToken, Direction, InsertPosition, SmolStr, SyntaxElement, SyntaxKind,
+    ted, AstToken, Direction, InsertPosition, NodeOrToken, SmolStr, SyntaxElement, SyntaxKind,
     SyntaxKind::{ATTR, COMMENT, WHITESPACE},
     SyntaxNode, SyntaxToken, T,
 };
@@ -29,37 +29,6 @@ impl ast::BinExpr {
     }
 }
 
-impl ast::Fn {
-    #[must_use]
-    pub fn with_body(&self, body: ast::BlockExpr) -> ast::Fn {
-        let mut to_insert: ArrayVec<SyntaxElement, 2> = ArrayVec::new();
-        let old_body_or_semi: SyntaxElement = if let Some(old_body) = self.body() {
-            old_body.syntax().clone().into()
-        } else if let Some(semi) = self.semicolon_token() {
-            to_insert.push(make::tokens::single_space().into());
-            semi.into()
-        } else {
-            to_insert.push(make::tokens::single_space().into());
-            to_insert.push(body.syntax().clone().into());
-            return self.insert_children(InsertPosition::Last, to_insert);
-        };
-        to_insert.push(body.syntax().clone().into());
-        self.replace_children(single_node(old_body_or_semi), to_insert)
-    }
-
-    #[must_use]
-    pub fn with_generic_param_list(&self, generic_args: ast::GenericParamList) -> ast::Fn {
-        if let Some(old) = self.generic_param_list() {
-            return self.replace_descendant(old, generic_args);
-        }
-
-        let anchor = self.name().expect("The function must have a name").syntax().clone();
-
-        let to_insert = [generic_args.syntax().clone().into()];
-        self.insert_children(InsertPosition::After(anchor.into()), array::IntoIter::new(to_insert))
-    }
-}
-
 fn make_multiline<N>(node: N) -> N
 where
     N: AstNode + Clone,
@@ -92,81 +61,6 @@ where
     }
 }
 
-impl ast::Impl {
-    #[must_use]
-    pub fn with_assoc_item_list(&self, items: ast::AssocItemList) -> ast::Impl {
-        let mut to_insert: ArrayVec<SyntaxElement, 2> = ArrayVec::new();
-        if let Some(old_items) = self.assoc_item_list() {
-            let to_replace: SyntaxElement = old_items.syntax().clone().into();
-            to_insert.push(items.syntax().clone().into());
-            self.replace_children(single_node(to_replace), to_insert)
-        } else {
-            to_insert.push(make::tokens::single_space().into());
-            to_insert.push(items.syntax().clone().into());
-            self.insert_children(InsertPosition::Last, to_insert)
-        }
-    }
-}
-
-impl ast::AssocItemList {
-    #[must_use]
-    pub fn append_items(
-        &self,
-        items: impl IntoIterator<Item = ast::AssocItem>,
-    ) -> ast::AssocItemList {
-        let mut res = self.clone();
-        if !self.syntax().text().contains_char('\n') {
-            res = make_multiline(res);
-        }
-        items.into_iter().for_each(|it| res = res.append_item(it));
-        res.fixup_trailing_whitespace().unwrap_or(res)
-    }
-
-    #[must_use]
-    pub fn append_item(&self, item: ast::AssocItem) -> ast::AssocItemList {
-        let (indent, position, whitespace) = match self.assoc_items().last() {
-            Some(it) => (
-                leading_indent(it.syntax()).unwrap_or_default().to_string(),
-                InsertPosition::After(it.syntax().clone().into()),
-                "\n\n",
-            ),
-            None => match self.l_curly_token() {
-                Some(it) => (
-                    "    ".to_string() + &leading_indent(self.syntax()).unwrap_or_default(),
-                    InsertPosition::After(it.into()),
-                    "\n",
-                ),
-                None => return self.clone(),
-            },
-        };
-        let ws = tokens::WsBuilder::new(&format!("{}{}", whitespace, indent));
-        let to_insert: ArrayVec<SyntaxElement, 2> =
-            [ws.ws().into(), item.syntax().clone().into()].into();
-        self.insert_children(position, to_insert)
-    }
-
-    /// Remove extra whitespace between last item and closing curly brace.
-    fn fixup_trailing_whitespace(&self) -> Option<ast::AssocItemList> {
-        let first_token_after_items =
-            self.assoc_items().last()?.syntax().next_sibling_or_token()?;
-        let last_token_before_curly = self.r_curly_token()?.prev_sibling_or_token()?;
-        if last_token_before_curly != first_token_after_items {
-            // there is something more between last item and
-            // right curly than just whitespace - bail out
-            return None;
-        }
-        let whitespace =
-            last_token_before_curly.clone().into_token().and_then(ast::Whitespace::cast)?;
-        let text = whitespace.syntax().text();
-        let newline = text.rfind('\n')?;
-        let keep = tokens::WsBuilder::new(&text[newline..]);
-        Some(self.replace_children(
-            first_token_after_items..=last_token_before_curly,
-            std::iter::once(keep.ws().into()),
-        ))
-    }
-}
-
 impl ast::RecordExprFieldList {
     #[must_use]
     pub fn append_field(&self, field: &ast::RecordExprField) -> ast::RecordExprFieldList {
@@ -243,36 +137,6 @@ impl ast::RecordExprFieldList {
     }
 }
 
-impl ast::TypeAlias {
-    #[must_use]
-    pub fn remove_bounds(&self) -> ast::TypeAlias {
-        let colon = match self.colon_token() {
-            Some(it) => it,
-            None => return self.clone(),
-        };
-        let end = match self.type_bound_list() {
-            Some(it) => it.syntax().clone().into(),
-            None => colon.clone().into(),
-        };
-        self.replace_children(colon.into()..=end, iter::empty())
-    }
-}
-
-impl ast::TypeParam {
-    #[must_use]
-    pub fn remove_bounds(&self) -> ast::TypeParam {
-        let colon = match self.colon_token() {
-            Some(it) => it,
-            None => return self.clone(),
-        };
-        let end = match self.type_bound_list() {
-            Some(it) => it.syntax().clone().into(),
-            None => colon.clone().into(),
-        };
-        self.replace_children(colon.into()..=end, iter::empty())
-    }
-}
-
 impl ast::Path {
     #[must_use]
     pub fn with_segment(&self, segment: ast::PathSegment) -> ast::Path {
@@ -313,33 +177,7 @@ impl ast::PathSegment {
     }
 }
 
-impl ast::Use {
-    #[must_use]
-    pub fn with_use_tree(&self, use_tree: ast::UseTree) -> ast::Use {
-        if let Some(old) = self.use_tree() {
-            return self.replace_descendant(old, use_tree);
-        }
-        self.clone()
-    }
-}
-
 impl ast::UseTree {
-    #[must_use]
-    pub fn with_path(&self, path: ast::Path) -> ast::UseTree {
-        if let Some(old) = self.path() {
-            return self.replace_descendant(old, path);
-        }
-        self.clone()
-    }
-
-    #[must_use]
-    pub fn with_use_tree_list(&self, use_tree_list: ast::UseTreeList) -> ast::UseTree {
-        if let Some(old) = self.use_tree_list() {
-            return self.replace_descendant(old, use_tree_list);
-        }
-        self.clone()
-    }
-
     /// Splits off the given prefix, making it the path component of the use tree, appending the rest of the path to all UseTreeList items.
     #[must_use]
     pub fn split_prefix(&self, prefix: &ast::Path) -> ast::UseTree {
@@ -449,61 +287,6 @@ impl ast::MatchArmList {
     }
 }
 
-impl ast::GenericParamList {
-    #[must_use]
-    pub fn append_params(
-        &self,
-        params: impl IntoIterator<Item = ast::GenericParam>,
-    ) -> ast::GenericParamList {
-        let mut res = self.clone();
-        params.into_iter().for_each(|it| res = res.append_param(it));
-        res
-    }
-
-    #[must_use]
-    pub fn append_param(&self, item: ast::GenericParam) -> ast::GenericParamList {
-        let space = tokens::single_space();
-
-        let mut to_insert: ArrayVec<SyntaxElement, 4> = ArrayVec::new();
-        if self.generic_params().next().is_some() {
-            to_insert.push(space.into());
-        }
-        to_insert.push(item.syntax().clone().into());
-
-        macro_rules! after_l_angle {
-            () => {{
-                let anchor = match self.l_angle_token() {
-                    Some(it) => it.into(),
-                    None => return self.clone(),
-                };
-                InsertPosition::After(anchor)
-            }};
-        }
-
-        macro_rules! after_field {
-            ($anchor:expr) => {
-                if let Some(comma) = $anchor
-                    .syntax()
-                    .siblings_with_tokens(Direction::Next)
-                    .find(|it| it.kind() == T![,])
-                {
-                    InsertPosition::After(comma)
-                } else {
-                    to_insert.insert(0, make::token(T![,]).into());
-                    InsertPosition::After($anchor.syntax().clone().into())
-                }
-            };
-        }
-
-        let position = match self.generic_params().last() {
-            Some(it) => after_field!(it),
-            None => after_l_angle!(),
-        };
-
-        self.insert_children(position, to_insert)
-    }
-}
-
 #[must_use]
 pub fn remove_attrs_and_docs<N: ast::AttrsOwner>(node: &N) -> N {
     N::cast(remove_attrs_and_docs_inner(node.syntax().clone())).unwrap()
@@ -554,6 +337,12 @@ impl ops::Add<u8> for IndentLevel {
 }
 
 impl IndentLevel {
+    pub fn single() -> IndentLevel {
+        IndentLevel(0)
+    }
+    pub fn is_zero(&self) -> bool {
+        self.0 == 0
+    }
     pub fn from_element(element: &SyntaxElement) -> IndentLevel {
         match element {
             rowan::NodeOrToken::Node(it) => IndentLevel::from_node(it),
@@ -588,37 +377,39 @@ impl IndentLevel {
     /// ```
     /// if you indent the block, the `{` token would stay put.
     fn increase_indent(self, node: SyntaxNode) -> SyntaxNode {
-        let mut rewriter = SyntaxRewriter::default();
-        node.descendants_with_tokens()
-            .filter_map(|el| el.into_token())
-            .filter_map(ast::Whitespace::cast)
-            .filter(|ws| {
-                let text = ws.syntax().text();
-                text.contains('\n')
-            })
-            .for_each(|ws| {
-                let new_ws = make::tokens::whitespace(&format!("{}{}", ws.syntax(), self,));
-                rewriter.replace(ws.syntax(), &new_ws)
-            });
-        rewriter.rewrite(&node)
+        let res = node.clone_subtree().clone_for_update();
+        let tokens = res.preorder_with_tokens().filter_map(|event| match event {
+            rowan::WalkEvent::Leave(NodeOrToken::Token(it)) => Some(it),
+            _ => None,
+        });
+        for token in tokens {
+            if let Some(ws) = ast::Whitespace::cast(token) {
+                if ws.text().contains('\n') {
+                    let new_ws = make::tokens::whitespace(&format!("{}{}", ws.syntax(), self));
+                    ted::replace(ws.syntax(), &new_ws)
+                }
+            }
+        }
+        res.clone_subtree()
     }
 
     fn decrease_indent(self, node: SyntaxNode) -> SyntaxNode {
-        let mut rewriter = SyntaxRewriter::default();
-        node.descendants_with_tokens()
-            .filter_map(|el| el.into_token())
-            .filter_map(ast::Whitespace::cast)
-            .filter(|ws| {
-                let text = ws.syntax().text();
-                text.contains('\n')
-            })
-            .for_each(|ws| {
-                let new_ws = make::tokens::whitespace(
-                    &ws.syntax().text().replace(&format!("\n{}", self), "\n"),
-                );
-                rewriter.replace(ws.syntax(), &new_ws)
-            });
-        rewriter.rewrite(&node)
+        let res = node.clone_subtree().clone_for_update();
+        let tokens = res.preorder_with_tokens().filter_map(|event| match event {
+            rowan::WalkEvent::Leave(NodeOrToken::Token(it)) => Some(it),
+            _ => None,
+        });
+        for token in tokens {
+            if let Some(ws) = ast::Whitespace::cast(token) {
+                if ws.text().contains('\n') {
+                    let new_ws = make::tokens::whitespace(
+                        &ws.syntax().text().replace(&format!("\n{}", self), "\n"),
+                    );
+                    ted::replace(ws.syntax(), &new_ws)
+                }
+            }
+        }
+        res.clone_subtree()
     }
 }
 
@@ -662,13 +453,6 @@ pub trait AstNodeEdit: AstNode + Clone + Sized {
         let new_syntax = algo::replace_children(self.syntax(), to_replace, to_insert);
         Self::cast(new_syntax).unwrap()
     }
-
-    #[must_use]
-    fn replace_descendant<D: AstNode>(&self, old: D, new: D) -> Self {
-        let mut rewriter = SyntaxRewriter::default();
-        rewriter.replace(old.syntax(), new.syntax());
-        rewriter.rewrite_ast(self)
-    }
     fn indent_level(&self) -> IndentLevel {
         IndentLevel::from_node(self.syntax())
     }
diff --git a/crates/syntax/src/ast/edit_in_place.rs b/crates/syntax/src/ast/edit_in_place.rs
index 168355555..ca777d057 100644
--- a/crates/syntax/src/ast/edit_in_place.rs
+++ b/crates/syntax/src/ast/edit_in_place.rs
@@ -2,11 +2,16 @@
 
 use std::iter::empty;
 
-use parser::T;
+use parser::{SyntaxKind, T};
+use rowan::SyntaxElement;
 
 use crate::{
     algo::neighbor,
-    ast::{self, edit::AstNodeEdit, make, GenericParamsOwner, WhereClause},
+    ast::{
+        self,
+        edit::{AstNodeEdit, IndentLevel},
+        make, GenericParamsOwner,
+    },
     ted::{self, Position},
     AstNode, AstToken, Direction,
 };
@@ -37,7 +42,7 @@ impl GenericParamsOwnerEdit for ast::Fn {
         }
     }
 
-    fn get_or_create_where_clause(&self) -> WhereClause {
+    fn get_or_create_where_clause(&self) -> ast::WhereClause {
         if self.where_clause().is_none() {
             let position = if let Some(ty) = self.ret_type() {
                 Position::after(ty.syntax())
@@ -67,7 +72,7 @@ impl GenericParamsOwnerEdit for ast::Impl {
         }
     }
 
-    fn get_or_create_where_clause(&self) -> WhereClause {
+    fn get_or_create_where_clause(&self) -> ast::WhereClause {
         if self.where_clause().is_none() {
             let position = if let Some(items) = self.assoc_item_list() {
                 Position::before(items.syntax())
@@ -97,7 +102,7 @@ impl GenericParamsOwnerEdit for ast::Trait {
         }
     }
 
-    fn get_or_create_where_clause(&self) -> WhereClause {
+    fn get_or_create_where_clause(&self) -> ast::WhereClause {
         if self.where_clause().is_none() {
             let position = if let Some(items) = self.assoc_item_list() {
                 Position::before(items.syntax())
@@ -127,7 +132,7 @@ impl GenericParamsOwnerEdit for ast::Struct {
         }
     }
 
-    fn get_or_create_where_clause(&self) -> WhereClause {
+    fn get_or_create_where_clause(&self) -> ast::WhereClause {
         if self.where_clause().is_none() {
             let tfl = self.field_list().and_then(|fl| match fl {
                 ast::FieldList::RecordFieldList(_) => None,
@@ -165,7 +170,7 @@ impl GenericParamsOwnerEdit for ast::Enum {
         }
     }
 
-    fn get_or_create_where_clause(&self) -> WhereClause {
+    fn get_or_create_where_clause(&self) -> ast::WhereClause {
         if self.where_clause().is_none() {
             let position = if let Some(gpl) = self.generic_param_list() {
                 Position::after(gpl.syntax())
@@ -272,6 +277,75 @@ impl ast::Use {
     }
 }
 
+impl ast::Impl {
+    pub fn get_or_create_assoc_item_list(&self) -> ast::AssocItemList {
+        if self.assoc_item_list().is_none() {
+            let assoc_item_list = make::assoc_item_list().clone_for_update();
+            ted::append_child(self.syntax(), assoc_item_list.syntax());
+        }
+        self.assoc_item_list().unwrap()
+    }
+}
+
+impl ast::AssocItemList {
+    pub fn add_item(&self, item: ast::AssocItem) {
+        let (indent, position, whitespace) = match self.assoc_items().last() {
+            Some(last_item) => (
+                IndentLevel::from_node(last_item.syntax()),
+                Position::after(last_item.syntax()),
+                "\n\n",
+            ),
+            None => match self.l_curly_token() {
+                Some(l_curly) => {
+                    self.normalize_ws_between_braces();
+                    (IndentLevel::from_token(&l_curly) + 1, Position::after(&l_curly), "\n")
+                }
+                None => (IndentLevel::single(), Position::last_child_of(self.syntax()), "\n"),
+            },
+        };
+        let elements: Vec<SyntaxElement<_>> = vec![
+            make::tokens::whitespace(&format!("{}{}", whitespace, indent)).into(),
+            item.syntax().clone().into(),
+        ];
+        ted::insert_all(position, elements);
+    }
+
+    fn normalize_ws_between_braces(&self) -> Option<()> {
+        let l = self.l_curly_token()?;
+        let r = self.r_curly_token()?;
+        let indent = IndentLevel::from_node(self.syntax());
+
+        match l.next_sibling_or_token() {
+            Some(ws) if ws.kind() == SyntaxKind::WHITESPACE => {
+                if ws.next_sibling_or_token()?.into_token()? == r {
+                    ted::replace(ws, make::tokens::whitespace(&format!("\n{}", indent)));
+                }
+            }
+            Some(ws) if ws.kind() == T!['}'] => {
+                ted::insert(Position::after(l), make::tokens::whitespace(&format!("\n{}", indent)));
+            }
+            _ => (),
+        }
+        Some(())
+    }
+}
+
+impl ast::Fn {
+    pub fn get_or_create_body(&self) -> ast::BlockExpr {
+        if self.body().is_none() {
+            let body = make::ext::empty_block_expr().clone_for_update();
+            match self.semicolon_token() {
+                Some(semi) => {
+                    ted::replace(semi, body.syntax());
+                    ted::insert(Position::before(body.syntax), make::tokens::single_space());
+                }
+                None => ted::append_child(self.syntax(), body.syntax()),
+            }
+        }
+        self.body().unwrap()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use std::fmt;
diff --git a/crates/syntax/src/ast/make.rs b/crates/syntax/src/ast/make.rs
index 1998ad1f6..d13926ded 100644
--- a/crates/syntax/src/ast/make.rs
+++ b/crates/syntax/src/ast/make.rs
@@ -12,7 +12,7 @@
 use itertools::Itertools;
 use stdx::{format_to, never};
 
-use crate::{ast, AstNode, SourceFile, SyntaxKind, SyntaxNode, SyntaxToken};
+use crate::{ast, AstNode, SourceFile, SyntaxKind, SyntaxToken};
 
 /// While the parent module defines basic atomic "constructors", the `ext`
 /// module defines shortcuts for common things.
@@ -99,7 +99,7 @@ fn ty_from_text(text: &str) -> ast::Type {
 }
 
 pub fn assoc_item_list() -> ast::AssocItemList {
-    ast_from_text("impl C for D {};")
+    ast_from_text("impl C for D {}")
 }
 
 pub fn impl_trait(trait_: ast::Path, ty: ast::Path) -> ast::Impl {
@@ -601,17 +601,11 @@ fn ast_from_text<N: AstNode>(text: &str) -> N {
             panic!("Failed to make ast node `{}` from text {}", std::any::type_name::<N>(), text)
         }
     };
-    let node = node.syntax().clone();
-    let node = unroot(node);
-    let node = N::cast(node).unwrap();
+    let node = node.clone_subtree();
     assert_eq!(node.syntax().text_range().start(), 0.into());
     node
 }
 
-fn unroot(n: SyntaxNode) -> SyntaxNode {
-    SyntaxNode::new_root(n.green().into())
-}
-
 pub fn token(kind: SyntaxKind) -> SyntaxToken {
     tokens::SOURCE_FILE
         .tree()
diff --git a/crates/syntax/src/parsing.rs b/crates/syntax/src/parsing.rs
index 333bde54a..431ed0699 100644
--- a/crates/syntax/src/parsing.rs
+++ b/crates/syntax/src/parsing.rs
@@ -6,14 +6,13 @@ mod text_token_source;
 mod text_tree_sink;
 mod reparsing;
 
-use crate::{syntax_node::GreenNode, AstNode, SyntaxError, SyntaxNode};
+use parser::SyntaxKind;
 use text_token_source::TextTokenSource;
 use text_tree_sink::TextTreeSink;
 
-pub(crate) use lexer::*;
+use crate::{syntax_node::GreenNode, AstNode, SyntaxError, SyntaxNode};
 
-pub(crate) use self::reparsing::incremental_reparse;
-use parser::SyntaxKind;
+pub(crate) use crate::parsing::{lexer::*, reparsing::incremental_reparse};
 
 pub(crate) fn parse_text(text: &str) -> (GreenNode, Vec<SyntaxError>) {
     let (tokens, lexer_errors) = tokenize(&text);