3 files changed, 33 insertions, 53 deletions

diff --git a/crates/ide_assists/src/utils.rs b/crates/ide_assists/src/utils.rs
index 7d562d1d4..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,
 };
@@ -139,34 +139,32 @@ pub fn add_trait_assoc_items_to_impl(
         .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).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 {
-        if first_item.is_none() {
-            first_item = Some(item.clone())
-        }
-        assoc_item_list.add_item(item)
-    }
-    return (res, first_item.unwrap());
-
-    fn add_body(fn_def: ast::Fn) -> ast::Fn {
-        match fn_def.body() {
-            Some(_) => fn_def,
-            None => {
+        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/syntax/src/ast/edit.rs b/crates/syntax/src/ast/edit.rs
index 7e4b8252e..4b5f5c571 100644
--- a/crates/syntax/src/ast/edit.rs
+++ b/crates/syntax/src/ast/edit.rs
@@ -13,7 +13,7 @@ use crate::{
     ast::{
         self,
         make::{self, tokens},
-        AstNode, TypeBoundsOwner,
+        AstNode,
     },
     ted, AstToken, Direction, InsertPosition, NodeOrToken, SmolStr, SyntaxElement, SyntaxKind,
     SyntaxKind::{ATTR, COMMENT, WHITESPACE},
@@ -29,25 +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)
-    }
-}
-
 fn make_multiline<N>(node: N) -> N
 where
     N: AstNode + Clone,
@@ -156,21 +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::Path {
     #[must_use]
     pub fn with_segment(&self, segment: ast::PathSegment) -> ast::Path {
diff --git a/crates/syntax/src/ast/edit_in_place.rs b/crates/syntax/src/ast/edit_in_place.rs
index 9812e00c9..ca777d057 100644
--- a/crates/syntax/src/ast/edit_in_place.rs
+++ b/crates/syntax/src/ast/edit_in_place.rs
@@ -330,6 +330,22 @@ impl ast::AssocItemList {
     }
 }
 
+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;