23 files changed, 999 insertions, 627 deletions

diff --git a/crates/assists/src/assist_context.rs b/crates/assists/src/assist_context.rs
index a1c0550e4..a17e592b0 100644
--- a/crates/assists/src/assist_context.rs
+++ b/crates/assists/src/assist_context.rs
@@ -12,7 +12,7 @@ use ide_db::{
 };
 use syntax::{
     algo::{self, find_node_at_offset, SyntaxRewriter},
-    AstNode, SourceFile, SyntaxElement, SyntaxKind, SyntaxToken, TextRange, TextSize,
+    AstNode, AstToken, SourceFile, SyntaxElement, SyntaxKind, SyntaxToken, TextRange, TextSize,
     TokenAtOffset,
 };
 use text_edit::{TextEdit, TextEditBuilder};
@@ -81,9 +81,12 @@ impl<'a> AssistContext<'a> {
     pub(crate) fn token_at_offset(&self) -> TokenAtOffset<SyntaxToken> {
         self.source_file.syntax().token_at_offset(self.offset())
     }
-    pub(crate) fn find_token_at_offset(&self, kind: SyntaxKind) -> Option<SyntaxToken> {
+    pub(crate) fn find_token_syntax_at_offset(&self, kind: SyntaxKind) -> Option<SyntaxToken> {
         self.token_at_offset().find(|it| it.kind() == kind)
     }
+    pub(crate) fn find_token_at_offset<T: AstToken>(&self) -> Option<T> {
+        self.token_at_offset().find_map(T::cast)
+    }
     pub(crate) fn find_node_at_offset<N: AstNode>(&self) -> Option<N> {
         find_node_at_offset(self.source_file.syntax(), self.offset())
     }
@@ -279,12 +282,6 @@ impl AssistBuilder {
         algo::diff(&node, &new).into_text_edit(&mut self.edit);
     }
 
-    // FIXME: kill this API
-    /// Get access to the raw `TextEditBuilder`.
-    pub(crate) fn text_edit_builder(&mut self) -> &mut TextEditBuilder {
-        &mut self.edit
-    }
-
     fn finish(mut self) -> SourceChange {
         self.commit();
         SourceChange {
diff --git a/crates/assists/src/handlers/add_custom_impl.rs b/crates/assists/src/handlers/add_custom_impl.rs
index 8757fa33f..c13493fd8 100644
--- a/crates/assists/src/handlers/add_custom_impl.rs
+++ b/crates/assists/src/handlers/add_custom_impl.rs
@@ -1,13 +1,18 @@
+use ide_db::imports_locator;
 use itertools::Itertools;
 use syntax::{
-    ast::{self, AstNode},
+    ast::{self, make, AstNode},
     Direction, SmolStr,
     SyntaxKind::{IDENT, WHITESPACE},
-    TextRange, TextSize,
+    TextSize,
 };
 
 use crate::{
-    assist_context::{AssistContext, Assists},
+    assist_context::{AssistBuilder, AssistContext, Assists},
+    utils::{
+        add_trait_assoc_items_to_impl, filter_assoc_items, mod_path_to_ast, render_snippet, Cursor,
+        DefaultMethods,
+    },
     AssistId, AssistKind,
 };
 
@@ -30,72 +35,154 @@ use crate::{
 // ```
 pub(crate) fn add_custom_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let attr = ctx.find_node_at_offset::<ast::Attr>()?;
-    let input = attr.token_tree()?;
 
     let attr_name = attr
         .syntax()
         .descendants_with_tokens()
         .filter(|t| t.kind() == IDENT)
-        .find_map(|i| i.into_token())
-        .filter(|t| *t.text() == "derive")?
+        .find_map(syntax::NodeOrToken::into_token)
+        .filter(|t| t.text() == "derive")?
         .text()
         .clone();
 
     let trait_token =
         ctx.token_at_offset().find(|t| t.kind() == IDENT && *t.text() != attr_name)?;
+    let trait_path = make::path_unqualified(make::path_segment(make::name_ref(trait_token.text())));
+
+    let annotated_name = attr.syntax().siblings(Direction::Next).find_map(ast::Name::cast)?;
+    let insert_pos = annotated_name.syntax().parent()?.text_range().end();
+
+    let current_module = ctx.sema.scope(annotated_name.syntax()).module()?;
+    let current_crate = current_module.krate();
 
-    let annotated = attr.syntax().siblings(Direction::Next).find_map(ast::Name::cast)?;
-    let annotated_name = annotated.syntax().text().to_string();
-    let start_offset = annotated.syntax().parent()?.text_range().end();
+    let found_traits = imports_locator::find_imports(&ctx.sema, current_crate, trait_token.text())
+        .into_iter()
+        .filter_map(|candidate: either::Either<hir::ModuleDef, hir::MacroDef>| match candidate {
+            either::Either::Left(hir::ModuleDef::Trait(trait_)) => Some(trait_),
+            _ => None,
+        })
+        .flat_map(|trait_| {
+            current_module
+                .find_use_path(ctx.sema.db, hir::ModuleDef::Trait(trait_))
+                .as_ref()
+                .map(mod_path_to_ast)
+                .zip(Some(trait_))
+        });
 
-    let label =
-        format!("Add custom impl `{}` for `{}`", trait_token.text().as_str(), annotated_name);
+    let mut no_traits_found = true;
+    for (trait_path, trait_) in found_traits.inspect(|_| no_traits_found = false) {
+        add_assist(acc, ctx, &attr, &trait_path, Some(trait_), &annotated_name, insert_pos)?;
+    }
+    if no_traits_found {
+        add_assist(acc, ctx, &attr, &trait_path, None, &annotated_name, insert_pos)?;
+    }
+    Some(())
+}
 
+fn add_assist(
+    acc: &mut Assists,
+    ctx: &AssistContext,
+    attr: &ast::Attr,
+    trait_path: &ast::Path,
+    trait_: Option<hir::Trait>,
+    annotated_name: &ast::Name,
+    insert_pos: TextSize,
+) -> Option<()> {
     let target = attr.syntax().text_range();
+    let input = attr.token_tree()?;
+    let label = format!("Add custom impl `{}` for `{}`", trait_path, annotated_name);
+    let trait_name = trait_path.segment().and_then(|seg| seg.name_ref())?;
+
     acc.add(AssistId("add_custom_impl", AssistKind::Refactor), label, target, |builder| {
-        let new_attr_input = input
-            .syntax()
-            .descendants_with_tokens()
-            .filter(|t| t.kind() == IDENT)
-            .filter_map(|t| t.into_token().map(|t| t.text().clone()))
-            .filter(|t| t != trait_token.text())
-            .collect::<Vec<SmolStr>>();
-        let has_more_derives = !new_attr_input.is_empty();
-
-        if has_more_derives {
-            let new_attr_input = format!("({})", new_attr_input.iter().format(", "));
-            builder.replace(input.syntax().text_range(), new_attr_input);
-        } else {
-            let attr_range = attr.syntax().text_range();
-            builder.delete(attr_range);
-
-            let line_break_range = attr
-                .syntax()
-                .next_sibling_or_token()
-                .filter(|t| t.kind() == WHITESPACE)
-                .map(|t| t.text_range())
-                .unwrap_or_else(|| TextRange::new(TextSize::from(0), TextSize::from(0)));
-            builder.delete(line_break_range);
-        }
+        let impl_def_with_items =
+            impl_def_from_trait(&ctx.sema, annotated_name, trait_, trait_path);
+        update_attribute(builder, &input, &trait_name, &attr);
+        match (ctx.config.snippet_cap, impl_def_with_items) {
+            (None, _) => builder.insert(
+                insert_pos,
+                format!("\n\nimpl {} for {} {{\n\n}}", trait_path, annotated_name),
+            ),
+            (Some(cap), None) => builder.insert_snippet(
+                cap,
+                insert_pos,
+                format!("\n\nimpl {} for {} {{\n    $0\n}}", trait_path, annotated_name),
+            ),
+            (Some(cap), Some((impl_def, first_assoc_item))) => {
+                let mut cursor = Cursor::Before(first_assoc_item.syntax());
+                let placeholder;
+                if let ast::AssocItem::Fn(ref func) = first_assoc_item {
+                    if let Some(m) = func.syntax().descendants().find_map(ast::MacroCall::cast) {
+                        if m.syntax().text() == "todo!()" {
+                            placeholder = m;
+                            cursor = Cursor::Replace(placeholder.syntax());
+                        }
+                    }
+                }
 
-        match ctx.config.snippet_cap {
-            Some(cap) => {
                 builder.insert_snippet(
                     cap,
-                    start_offset,
-                    format!("\n\nimpl {} for {} {{\n    $0\n}}", trait_token, annotated_name),
-                );
-            }
-            None => {
-                builder.insert(
-                    start_offset,
-                    format!("\n\nimpl {} for {} {{\n\n}}", trait_token, annotated_name),
-                );
+                    insert_pos,
+                    format!("\n\n{}", render_snippet(cap, impl_def.syntax(), cursor)),
+                )
             }
-        }
+        };
     })
 }
 
+fn impl_def_from_trait(
+    sema: &hir::Semantics<ide_db::RootDatabase>,
+    annotated_name: &ast::Name,
+    trait_: Option<hir::Trait>,
+    trait_path: &ast::Path,
+) -> Option<(ast::Impl, ast::AssocItem)> {
+    let trait_ = trait_?;
+    let target_scope = sema.scope(annotated_name.syntax());
+    let trait_items = filter_assoc_items(sema.db, &trait_.items(sema.db), DefaultMethods::No);
+    if trait_items.is_empty() {
+        return None;
+    }
+    let impl_def = make::impl_trait(
+        trait_path.clone(),
+        make::path_unqualified(make::path_segment(make::name_ref(annotated_name.text()))),
+    );
+    let (impl_def, first_assoc_item) =
+        add_trait_assoc_items_to_impl(sema, trait_items, trait_, impl_def, target_scope);
+    Some((impl_def, first_assoc_item))
+}
+
+fn update_attribute(
+    builder: &mut AssistBuilder,
+    input: &ast::TokenTree,
+    trait_name: &ast::NameRef,
+    attr: &ast::Attr,
+) {
+    let new_attr_input = input
+        .syntax()
+        .descendants_with_tokens()
+        .filter(|t| t.kind() == IDENT)
+        .filter_map(|t| t.into_token().map(|t| t.text().clone()))
+        .filter(|t| t != trait_name.text())
+        .collect::<Vec<SmolStr>>();
+    let has_more_derives = !new_attr_input.is_empty();
+
+    if has_more_derives {
+        let new_attr_input = format!("({})", new_attr_input.iter().format(", "));
+        builder.replace(input.syntax().text_range(), new_attr_input);
+    } else {
+        let attr_range = attr.syntax().text_range();
+        builder.delete(attr_range);
+
+        if let Some(line_break_range) = attr
+            .syntax()
+            .next_sibling_or_token()
+            .filter(|t| t.kind() == WHITESPACE)
+            .map(|t| t.text_range())
+        {
+            builder.delete(line_break_range);
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::tests::{check_assist, check_assist_not_applicable};
@@ -103,6 +190,96 @@ mod tests {
     use super::*;
 
     #[test]
+    fn add_custom_impl_debug() {
+        check_assist(
+            add_custom_impl,
+            "
+mod fmt {
+    pub struct Error;
+    pub type Result = Result<(), Error>;
+    pub struct Formatter<'a>;
+    pub trait Debug {
+        fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+    }
+}
+
+#[derive(Debu<|>g)]
+struct Foo {
+    bar: String,
+}
+",
+            "
+mod fmt {
+    pub struct Error;
+    pub type Result = Result<(), Error>;
+    pub struct Formatter<'a>;
+    pub trait Debug {
+        fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+    }
+}
+
+struct Foo {
+    bar: String,
+}
+
+impl fmt::Debug for Foo {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        ${0:todo!()}
+    }
+}
+",
+        )
+    }
+    #[test]
+    fn add_custom_impl_all() {
+        check_assist(
+            add_custom_impl,
+            "
+mod foo {
+    pub trait Bar {
+        type Qux;
+        const Baz: usize = 42;
+        const Fez: usize;
+        fn foo();
+        fn bar() {}
+    }
+}
+
+#[derive(<|>Bar)]
+struct Foo {
+    bar: String,
+}
+",
+            "
+mod foo {
+    pub trait Bar {
+        type Qux;
+        const Baz: usize = 42;
+        const Fez: usize;
+        fn foo();
+        fn bar() {}
+    }
+}
+
+struct Foo {
+    bar: String,
+}
+
+impl foo::Bar for Foo {
+    $0type Qux;
+
+    const Baz: usize = 42;
+
+    const Fez: usize;
+
+    fn foo() {
+        todo!()
+    }
+}
+",
+        )
+    }
+    #[test]
     fn add_custom_impl_for_unique_input() {
         check_assist(
             add_custom_impl,
diff --git a/crates/assists/src/handlers/add_missing_impl_members.rs b/crates/assists/src/handlers/add_missing_impl_members.rs
index b82fb30ad..bbb71e261 100644
--- a/crates/assists/src/handlers/add_missing_impl_members.rs
+++ b/crates/assists/src/handlers/add_missing_impl_members.rs
@@ -1,27 +1,14 @@
-use hir::HasSource;
-use ide_db::traits::{get_missing_assoc_items, resolve_target_trait};
-use syntax::{
-    ast::{
-        self,
-        edit::{self, AstNodeEdit, IndentLevel},
-        make, AstNode, NameOwner,
-    },
-    SmolStr,
-};
+use ide_db::traits::resolve_target_trait;
+use syntax::ast::{self, AstNode};
 
 use crate::{
     assist_context::{AssistContext, Assists},
-    ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
-    utils::{render_snippet, Cursor},
+    utils::add_trait_assoc_items_to_impl,
+    utils::DefaultMethods,
+    utils::{filter_assoc_items, render_snippet, Cursor},
     AssistId, AssistKind,
 };
 
-#[derive(PartialEq)]
-enum AddMissingImplMembersMode {
-    DefaultMethodsOnly,
-    NoDefaultMethods,
-}
-
 // Assist: add_impl_missing_members
 //
 // Adds scaffold for required impl members.
@@ -55,7 +42,7 @@ pub(crate) fn add_missing_impl_members(acc: &mut Assists, ctx: &AssistContext) -
     add_missing_impl_members_inner(
         acc,
         ctx,
-        AddMissingImplMembersMode::NoDefaultMethods,
+        DefaultMethods::No,
         "add_impl_missing_members",
         "Implement missing members",
     )
@@ -97,7 +84,7 @@ pub(crate) fn add_missing_default_members(acc: &mut Assists, ctx: &AssistContext
     add_missing_impl_members_inner(
         acc,
         ctx,
-        AddMissingImplMembersMode::DefaultMethodsOnly,
+        DefaultMethods::Only,
         "add_impl_default_members",
         "Implement default members",
     )
@@ -106,7 +93,7 @@ pub(crate) fn add_missing_default_members(acc: &mut Assists, ctx: &AssistContext
 fn add_missing_impl_members_inner(
     acc: &mut Assists,
     ctx: &AssistContext,
-    mode: AddMissingImplMembersMode,
+    mode: DefaultMethods,
     assist_id: &'static str,
     label: &'static str,
 ) -> Option<()> {
@@ -114,32 +101,11 @@ fn add_missing_impl_members_inner(
     let impl_def = ctx.find_node_at_offset::<ast::Impl>()?;
     let trait_ = resolve_target_trait(&ctx.sema, &impl_def)?;
 
-    let def_name = |item: &ast::AssocItem| -> Option<SmolStr> {
-        match item {
-            ast::AssocItem::Fn(def) => def.name(),
-            ast::AssocItem::TypeAlias(def) => def.name(),
-            ast::AssocItem::Const(def) => def.name(),
-            ast::AssocItem::MacroCall(_) => None,
-        }
-        .map(|it| it.text().clone())
-    };
-
-    let missing_items = get_missing_assoc_items(&ctx.sema, &impl_def)
-        .iter()
-        .map(|i| match i {
-            hir::AssocItem::Function(i) => ast::AssocItem::Fn(i.source(ctx.db()).value),
-            hir::AssocItem::TypeAlias(i) => ast::AssocItem::TypeAlias(i.source(ctx.db()).value),
-            hir::AssocItem::Const(i) => ast::AssocItem::Const(i.source(ctx.db()).value),
-        })
-        .filter(|t| def_name(&t).is_some())
-        .filter(|t| match t {
-            ast::AssocItem::Fn(def) => match mode {
-                AddMissingImplMembersMode::DefaultMethodsOnly => def.body().is_some(),
-                AddMissingImplMembersMode::NoDefaultMethods => def.body().is_none(),
-            },
-            _ => mode == AddMissingImplMembersMode::NoDefaultMethods,
-        })
-        .collect::<Vec<_>>();
+    let missing_items = filter_assoc_items(
+        ctx.db(),
+        &ide_db::traits::get_missing_assoc_items(&ctx.sema, &impl_def),
+        mode,
+    );
 
     if missing_items.is_empty() {
         return None;
@@ -147,29 +113,9 @@ fn add_missing_impl_members_inner(
 
     let target = impl_def.syntax().text_range();
     acc.add(AssistId(assist_id, AssistKind::QuickFix), label, target, |builder| {
-        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 = ctx.sema.scope_for_def(trait_);
         let target_scope = ctx.sema.scope(impl_def.syntax());
-        let ast_transform = QualifyPaths::new(&target_scope, &source_scope)
-            .or(SubstituteTypeParams::for_trait_impl(&source_scope, trait_, impl_def.clone()));
-
-        let items = missing_items
-            .into_iter()
-            .map(|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();
-
+        let (new_impl_def, first_new_item) =
+            add_trait_assoc_items_to_impl(&ctx.sema, missing_items, trait_, impl_def, target_scope);
         match ctx.config.snippet_cap {
             None => builder.replace(target, new_impl_def.to_string()),
             Some(cap) => {
@@ -193,14 +139,6 @@ fn add_missing_impl_members_inner(
     })
 }
 
-fn add_body(fn_def: ast::Fn) -> ast::Fn {
-    if fn_def.body().is_some() {
-        return fn_def;
-    }
-    let body = make::block_expr(None, Some(make::expr_todo())).indent(IndentLevel(1));
-    fn_def.with_body(body)
-}
-
 #[cfg(test)]
 mod tests {
     use crate::tests::{check_assist, check_assist_not_applicable};
diff --git a/crates/assists/src/handlers/add_turbo_fish.rs b/crates/assists/src/handlers/add_turbo_fish.rs
index e3d84d698..1f486c013 100644
--- a/crates/assists/src/handlers/add_turbo_fish.rs
+++ b/crates/assists/src/handlers/add_turbo_fish.rs
@@ -25,7 +25,7 @@ use crate::{
 // }
 // ```
 pub(crate) fn add_turbo_fish(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let ident = ctx.find_token_at_offset(SyntaxKind::IDENT).or_else(|| {
+    let ident = ctx.find_token_syntax_at_offset(SyntaxKind::IDENT).or_else(|| {
         let arg_list = ctx.find_node_at_offset::<ast::ArgList>()?;
         if arg_list.args().count() > 0 {
             return None;
diff --git a/crates/assists/src/handlers/change_return_type_to_result.rs b/crates/assists/src/handlers/change_return_type_to_result.rs
index be480943c..76f33a5b6 100644
--- a/crates/assists/src/handlers/change_return_type_to_result.rs
+++ b/crates/assists/src/handlers/change_return_type_to_result.rs
@@ -2,7 +2,7 @@ use std::iter;
 
 use syntax::{
     ast::{self, make, BlockExpr, Expr, LoopBodyOwner},
-    AstNode, SyntaxNode,
+    match_ast, AstNode, SyntaxNode,
 };
 use test_utils::mark;
 
@@ -21,8 +21,18 @@ use crate::{AssistContext, AssistId, AssistKind, Assists};
 // ```
 pub(crate) fn change_return_type_to_result(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let ret_type = ctx.find_node_at_offset::<ast::RetType>()?;
-    // FIXME: extend to lambdas as well
-    let fn_def = ret_type.syntax().parent().and_then(ast::Fn::cast)?;
+    let parent = ret_type.syntax().parent()?;
+    let block_expr = match_ast! {
+        match parent {
+            ast::Fn(func) => func.body()?,
+            ast::ClosureExpr(closure) => match closure.body()? {
+                Expr::BlockExpr(block) => block,
+                // closures require a block when a return type is specified
+                _ => return None,
+            },
+            _ => return None,
+        }
+    };
 
     let type_ref = &ret_type.ty()?;
     let ret_type_str = type_ref.syntax().text().to_string();
@@ -34,16 +44,14 @@ pub(crate) fn change_return_type_to_result(acc: &mut Assists, ctx: &AssistContex
         }
     }
 
-    let block_expr = &fn_def.body()?;
-
     acc.add(
         AssistId("change_return_type_to_result", AssistKind::RefactorRewrite),
         "Wrap return type in Result",
         type_ref.syntax().text_range(),
         |builder| {
             let mut tail_return_expr_collector = TailReturnCollector::new();
-            tail_return_expr_collector.collect_jump_exprs(block_expr, false);
-            tail_return_expr_collector.collect_tail_exprs(block_expr);
+            tail_return_expr_collector.collect_jump_exprs(&block_expr, false);
+            tail_return_expr_collector.collect_tail_exprs(&block_expr);
 
             for ret_expr_arg in tail_return_expr_collector.exprs_to_wrap {
                 let ok_wrapped = make::expr_call(
@@ -285,16 +293,20 @@ mod tests {
     }
 
     #[test]
-    fn change_return_type_to_result_simple_return_type() {
+    fn change_return_type_to_result_simple_closure() {
         check_assist(
             change_return_type_to_result,
-            r#"fn foo() -> i32<|> {
-                let test = "test";
-                return 42i32;
+            r#"fn foo() {
+                || -> i32<|> {
+                    let test = "test";
+                    return 42i32;
+                };
             }"#,
-            r#"fn foo() -> Result<i32, ${0:_}> {
-                let test = "test";
-                return Ok(42i32);
+            r#"fn foo() {
+                || -> Result<i32, ${0:_}> {
+                    let test = "test";
+                    return Ok(42i32);
+                };
             }"#,
         );
     }
@@ -311,6 +323,29 @@ mod tests {
     }
 
     #[test]
+    fn change_return_type_to_result_simple_return_type_bad_cursor_closure() {
+        check_assist_not_applicable(
+            change_return_type_to_result,
+            r#"fn foo() {
+                || -> i32 {
+                    let test = "test";<|>
+                    return 42i32;
+                };
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_closure_non_block() {
+        check_assist_not_applicable(
+            change_return_type_to_result,
+            r#"fn foo() {
+                || -> i<|>32 3;
+            }"#,
+        );
+    }
+
+    #[test]
     fn change_return_type_to_result_simple_return_type_already_result_std() {
         check_assist_not_applicable(
             change_return_type_to_result,
@@ -334,6 +369,19 @@ mod tests {
     }
 
     #[test]
+    fn change_return_type_to_result_simple_return_type_already_result_closure() {
+        check_assist_not_applicable(
+            change_return_type_to_result,
+            r#"fn foo() {
+                || -> Result<i32<|>, String> {
+                    let test = "test";
+                    return 42i32;
+                };
+            }"#,
+        );
+    }
+
+    #[test]
     fn change_return_type_to_result_simple_with_cursor() {
         check_assist(
             change_return_type_to_result,
@@ -364,6 +412,25 @@ mod tests {
     }
 
     #[test]
+    fn change_return_type_to_result_simple_with_tail_closure() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() {
+                || -><|> i32 {
+                    let test = "test";
+                    42i32
+                };
+            }"#,
+            r#"fn foo() {
+                || -> Result<i32, ${0:_}> {
+                    let test = "test";
+                    Ok(42i32)
+                };
+            }"#,
+        );
+    }
+
+    #[test]
     fn change_return_type_to_result_simple_with_tail_only() {
         check_assist(
             change_return_type_to_result,
@@ -375,6 +442,7 @@ mod tests {
             }"#,
         );
     }
+
     #[test]
     fn change_return_type_to_result_simple_with_tail_block_like() {
         check_assist(
@@ -397,6 +465,31 @@ mod tests {
     }
 
     #[test]
+    fn change_return_type_to_result_simple_without_block_closure() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() {
+                || -> i32<|> {
+                    if true {
+                        42i32
+                    } else {
+                        24i32
+                    }
+                };
+            }"#,
+            r#"fn foo() {
+                || -> Result<i32, ${0:_}> {
+                    if true {
+                        Ok(42i32)
+                    } else {
+                        Ok(24i32)
+                    }
+                };
+            }"#,
+        );
+    }
+
+    #[test]
     fn change_return_type_to_result_simple_with_nested_if() {
         check_assist(
             change_return_type_to_result,
diff --git a/crates/assists/src/handlers/convert_integer_literal.rs b/crates/assists/src/handlers/convert_integer_literal.rs
index c8af80701..667115382 100644
--- a/crates/assists/src/handlers/convert_integer_literal.rs
+++ b/crates/assists/src/handlers/convert_integer_literal.rs
@@ -1,4 +1,4 @@
-use syntax::{ast, ast::Radix, AstNode};
+use syntax::{ast, ast::Radix, AstToken};
 
 use crate::{AssistContext, AssistId, AssistKind, Assists, GroupLabel};
 
@@ -15,14 +15,16 @@ use crate::{AssistContext, AssistId, AssistKind, Assists, GroupLabel};
 // ```
 pub(crate) fn convert_integer_literal(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let literal = ctx.find_node_at_offset::<ast::Literal>()?;
-    let (radix, value) = literal.int_value()?;
+    let literal = match literal.kind() {
+        ast::LiteralKind::IntNumber(it) => it,
+        _ => return None,
+    };
+    let radix = literal.radix();
+    let value = literal.value()?;
+    let suffix = literal.suffix();
 
     let range = literal.syntax().text_range();
     let group_id = GroupLabel("Convert integer base".into());
-    let suffix = match literal.kind() {
-        ast::LiteralKind::IntNumber { suffix } => suffix,
-        _ => return None,
-    };
 
     for &target_radix in Radix::ALL {
         if target_radix == radix {
@@ -36,16 +38,11 @@ pub(crate) fn convert_integer_literal(acc: &mut Assists, ctx: &AssistContext) ->
             Radix::Hexadecimal => format!("0x{:X}", value),
         };
 
-        let label = format!(
-            "Convert {} to {}{}",
-            literal,
-            converted,
-            suffix.as_deref().unwrap_or_default()
-        );
+        let label = format!("Convert {} to {}{}", literal, converted, suffix.unwrap_or_default());
 
         // Appends the type suffix back into the new literal if it exists.
-        if let Some(suffix) = &suffix {
-            converted.push_str(&suffix);
+        if let Some(suffix) = suffix {
+            converted.push_str(suffix);
         }
 
         acc.add_group(
@@ -132,34 +129,6 @@ mod tests {
         );
     }
 
-    // Decimal numbers under 3 digits have a special case where they return early because we can't fit a
-    // other base's prefix, so we have a separate test for that.
-    #[test]
-    fn convert_small_decimal_integer() {
-        let before = "const _: i32 = 10<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b1010;",
-            "Convert 10 to 0b1010",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o12;",
-            "Convert 10 to 0o12",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xA;",
-            "Convert 10 to 0xA",
-        );
-    }
-
     #[test]
     fn convert_hexadecimal_integer() {
         let before = "const _: i32 = 0xFF<|>;";
@@ -239,7 +208,7 @@ mod tests {
     }
 
     #[test]
-    fn convert_decimal_integer_with_underscores() {
+    fn convert_integer_with_underscores() {
         let before = "const _: i32 = 1_00_0<|>;";
 
         check_assist_by_label(
@@ -265,111 +234,7 @@ mod tests {
     }
 
     #[test]
-    fn convert_small_decimal_integer_with_underscores() {
-        let before = "const _: i32 = 1_0<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b1010;",
-            "Convert 1_0 to 0b1010",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o12;",
-            "Convert 1_0 to 0o12",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xA;",
-            "Convert 1_0 to 0xA",
-        );
-    }
-
-    #[test]
-    fn convert_hexadecimal_integer_with_underscores() {
-        let before = "const _: i32 = 0x_F_F<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b11111111;",
-            "Convert 0x_F_F to 0b11111111",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o377;",
-            "Convert 0x_F_F to 0o377",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 255;",
-            "Convert 0x_F_F to 255",
-        );
-    }
-
-    #[test]
-    fn convert_binary_integer_with_underscores() {
-        let before = "const _: i32 = 0b1111_1111<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o377;",
-            "Convert 0b1111_1111 to 0o377",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 255;",
-            "Convert 0b1111_1111 to 255",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xFF;",
-            "Convert 0b1111_1111 to 0xFF",
-        );
-    }
-
-    #[test]
-    fn convert_octal_integer_with_underscores() {
-        let before = "const _: i32 = 0o3_77<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b11111111;",
-            "Convert 0o3_77 to 0b11111111",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 255;",
-            "Convert 0o3_77 to 255",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xFF;",
-            "Convert 0o3_77 to 0xFF",
-        );
-    }
-
-    #[test]
-    fn convert_decimal_integer_with_suffix() {
+    fn convert_integer_with_suffix() {
         let before = "const _: i32 = 1000i32<|>;";
 
         check_assist_by_label(
@@ -395,240 +260,6 @@ mod tests {
     }
 
     #[test]
-    fn convert_small_decimal_integer_with_suffix() {
-        let before = "const _: i32 = 10i32<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b1010i32;",
-            "Convert 10i32 to 0b1010i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o12i32;",
-            "Convert 10i32 to 0o12i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xAi32;",
-            "Convert 10i32 to 0xAi32",
-        );
-    }
-
-    #[test]
-    fn convert_hexadecimal_integer_with_suffix() {
-        let before = "const _: i32 = 0xFFi32<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b11111111i32;",
-            "Convert 0xFFi32 to 0b11111111i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o377i32;",
-            "Convert 0xFFi32 to 0o377i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 255i32;",
-            "Convert 0xFFi32 to 255i32",
-        );
-    }
-
-    #[test]
-    fn convert_binary_integer_with_suffix() {
-        let before = "const _: i32 = 0b11111111i32<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o377i32;",
-            "Convert 0b11111111i32 to 0o377i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 255i32;",
-            "Convert 0b11111111i32 to 255i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xFFi32;",
-            "Convert 0b11111111i32 to 0xFFi32",
-        );
-    }
-
-    #[test]
-    fn convert_octal_integer_with_suffix() {
-        let before = "const _: i32 = 0o377i32<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b11111111i32;",
-            "Convert 0o377i32 to 0b11111111i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 255i32;",
-            "Convert 0o377i32 to 255i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xFFi32;",
-            "Convert 0o377i32 to 0xFFi32",
-        );
-    }
-
-    #[test]
-    fn convert_decimal_integer_with_underscores_and_suffix() {
-        let before = "const _: i32 = 1_00_0i32<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b1111101000i32;",
-            "Convert 1_00_0i32 to 0b1111101000i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o1750i32;",
-            "Convert 1_00_0i32 to 0o1750i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0x3E8i32;",
-            "Convert 1_00_0i32 to 0x3E8i32",
-        );
-    }
-
-    #[test]
-    fn convert_small_decimal_integer_with_underscores_and_suffix() {
-        let before = "const _: i32 = 1_0i32<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b1010i32;",
-            "Convert 1_0i32 to 0b1010i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o12i32;",
-            "Convert 1_0i32 to 0o12i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xAi32;",
-            "Convert 1_0i32 to 0xAi32",
-        );
-    }
-
-    #[test]
-    fn convert_hexadecimal_integer_with_underscores_and_suffix() {
-        let before = "const _: i32 = 0x_F_Fi32<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b11111111i32;",
-            "Convert 0x_F_Fi32 to 0b11111111i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o377i32;",
-            "Convert 0x_F_Fi32 to 0o377i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 255i32;",
-            "Convert 0x_F_Fi32 to 255i32",
-        );
-    }
-
-    #[test]
-    fn convert_binary_integer_with_underscores_and_suffix() {
-        let before = "const _: i32 = 0b1111_1111i32<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0o377i32;",
-            "Convert 0b1111_1111i32 to 0o377i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 255i32;",
-            "Convert 0b1111_1111i32 to 255i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xFFi32;",
-            "Convert 0b1111_1111i32 to 0xFFi32",
-        );
-    }
-
-    #[test]
-    fn convert_octal_integer_with_underscores_and_suffix() {
-        let before = "const _: i32 = 0o3_77i32<|>;";
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0b11111111i32;",
-            "Convert 0o3_77i32 to 0b11111111i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 255i32;",
-            "Convert 0o3_77i32 to 255i32",
-        );
-
-        check_assist_by_label(
-            convert_integer_literal,
-            before,
-            "const _: i32 = 0xFFi32;",
-            "Convert 0o3_77i32 to 0xFFi32",
-        );
-    }
-
-    #[test]
     fn convert_overflowing_literal() {
         let before = "const _: i32 =
             111111111111111111111111111111111111111111111111111111111111111111111111<|>;";
diff --git a/crates/assists/src/handlers/expand_glob_import.rs b/crates/assists/src/handlers/expand_glob_import.rs
index 316a58d88..f51a9a4ad 100644
--- a/crates/assists/src/handlers/expand_glob_import.rs
+++ b/crates/assists/src/handlers/expand_glob_import.rs
@@ -5,13 +5,13 @@ use ide_db::{
     search::SearchScope,
 };
 use syntax::{
-    algo,
+    algo::SyntaxRewriter,
     ast::{self, make},
     AstNode, Direction, SyntaxNode, SyntaxToken, T,
 };
 
 use crate::{
-    assist_context::{AssistBuilder, AssistContext, Assists},
+    assist_context::{AssistContext, Assists},
     AssistId, AssistKind,
 };
 
@@ -41,7 +41,7 @@ use crate::{
 // fn qux(bar: Bar, baz: Baz) {}
 // ```
 pub(crate) fn expand_glob_import(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let star = ctx.find_token_at_offset(T![*])?;
+    let star = ctx.find_token_syntax_at_offset(T![*])?;
     let (parent, mod_path) = find_parent_and_path(&star)?;
     let target_module = match ctx.sema.resolve_path(&mod_path)? {
         PathResolution::Def(ModuleDef::Module(it)) => it,
@@ -61,7 +61,9 @@ pub(crate) fn expand_glob_import(acc: &mut Assists, ctx: &AssistContext) -> Opti
         "Expand glob import",
         target.text_range(),
         |builder| {
-            replace_ast(builder, parent, mod_path, names_to_import);
+            let mut rewriter = SyntaxRewriter::default();
+            replace_ast(&mut rewriter, parent, mod_path, names_to_import);
+            builder.rewrite(rewriter);
         },
     )
 }
@@ -236,7 +238,7 @@ fn find_names_to_import(
 }
 
 fn replace_ast(
-    builder: &mut AssistBuilder,
+    rewriter: &mut SyntaxRewriter,
     parent: Either<ast::UseTree, ast::UseTreeList>,
     path: ast::Path,
     names_to_import: Vec<Name>,
@@ -264,32 +266,21 @@ fn replace_ast(
     match use_trees.as_slice() {
         [name] => {
             if let Some(end_path) = name.path() {
-                let replacement =
-                    make::use_tree(make::path_concat(path, end_path), None, None, false);
-
-                algo::diff(
-                    &parent.either(|n| n.syntax().clone(), |n| n.syntax().clone()),
-                    replacement.syntax(),
-                )
-                .into_text_edit(builder.text_edit_builder());
+                rewriter.replace_ast(
+                    &parent.left_or_else(|tl| tl.parent_use_tree()),
+                    &make::use_tree(make::path_concat(path, end_path), None, None, false),
+                );
             }
         }
-        names => {
-            let replacement = match parent {
-                Either::Left(_) => {
-                    make::use_tree(path, Some(make::use_tree_list(names.to_owned())), None, false)
-                        .syntax()
-                        .clone()
-                }
-                Either::Right(_) => make::use_tree_list(names.to_owned()).syntax().clone(),
-            };
-
-            algo::diff(
-                &parent.either(|n| n.syntax().clone(), |n| n.syntax().clone()),
-                &replacement,
-            )
-            .into_text_edit(builder.text_edit_builder());
-        }
+        names => match &parent {
+            Either::Left(parent) => rewriter.replace_ast(
+                parent,
+                &make::use_tree(path, Some(make::use_tree_list(names.to_owned())), None, false),
+            ),
+            Either::Right(parent) => {
+                rewriter.replace_ast(parent, &make::use_tree_list(names.to_owned()))
+            }
+        },
     };
 }
 
@@ -884,4 +875,33 @@ fn qux(baz: Baz) {}
     ",
         )
     }
+
+    #[test]
+    fn expanding_glob_import_single_nested_glob_only() {
+        check_assist(
+            expand_glob_import,
+            r"
+mod foo {
+    pub struct Bar;
+}
+
+use foo::{*<|>};
+
+struct Baz {
+    bar: Bar
+}
+",
+            r"
+mod foo {
+    pub struct Bar;
+}
+
+use foo::Bar;
+
+struct Baz {
+    bar: Bar
+}
+",
+        );
+    }
 }
diff --git a/crates/assists/src/handlers/extract_struct_from_enum_variant.rs b/crates/assists/src/handlers/extract_struct_from_enum_variant.rs
index dddab255e..14209b771 100644
--- a/crates/assists/src/handlers/extract_struct_from_enum_variant.rs
+++ b/crates/assists/src/handlers/extract_struct_from_enum_variant.rs
@@ -1,3 +1,6 @@
+use std::iter;
+
+use either::Either;
 use hir::{AsName, EnumVariant, Module, ModuleDef, Name};
 use ide_db::{defs::Definition, search::Reference, RootDatabase};
 use rustc_hash::{FxHashMap, FxHashSet};
@@ -31,40 +34,32 @@ pub(crate) fn extract_struct_from_enum_variant(
     ctx: &AssistContext,
 ) -> Option<()> {
     let variant = ctx.find_node_at_offset::<ast::Variant>()?;
-    let field_list = match variant.kind() {
-        ast::StructKind::Tuple(field_list) => field_list,
-        _ => return None,
-    };
-
-    // skip 1-tuple variants
-    if field_list.fields().count() == 1 {
-        return None;
-    }
+    let field_list = extract_field_list_if_applicable(&variant)?;
 
     let variant_name = variant.name()?;
     let variant_hir = ctx.sema.to_def(&variant)?;
-    if existing_struct_def(ctx.db(), &variant_name, &variant_hir) {
+    if existing_definition(ctx.db(), &variant_name, &variant_hir) {
         return None;
     }
+
     let enum_ast = variant.parent_enum();
-    let visibility = enum_ast.visibility();
     let enum_hir = ctx.sema.to_def(&enum_ast)?;
-    let variant_hir_name = variant_hir.name(ctx.db());
-    let enum_module_def = ModuleDef::from(enum_hir);
-    let current_module = enum_hir.module(ctx.db());
     let target = variant.syntax().text_range();
     acc.add(
         AssistId("extract_struct_from_enum_variant", AssistKind::RefactorRewrite),
         "Extract struct from enum variant",
         target,
         |builder| {
-            let definition = Definition::ModuleDef(ModuleDef::EnumVariant(variant_hir));
-            let res = definition.usages(&ctx.sema).all();
+            let variant_hir_name = variant_hir.name(ctx.db());
+            let enum_module_def = ModuleDef::from(enum_hir);
+            let usages =
+                Definition::ModuleDef(ModuleDef::EnumVariant(variant_hir)).usages(&ctx.sema).all();
 
             let mut visited_modules_set = FxHashSet::default();
+            let current_module = enum_hir.module(ctx.db());
             visited_modules_set.insert(current_module);
             let mut rewriters = FxHashMap::default();
-            for reference in res {
+            for reference in usages {
                 let rewriter = rewriters
                     .entry(reference.file_range.file_id)
                     .or_insert_with(SyntaxRewriter::default);
@@ -86,26 +81,49 @@ pub(crate) fn extract_struct_from_enum_variant(
                 builder.rewrite(rewriter);
             }
             builder.edit_file(ctx.frange.file_id);
-            update_variant(&mut rewriter, &variant_name, &field_list);
+            update_variant(&mut rewriter, &variant);
             extract_struct_def(
                 &mut rewriter,
                 &enum_ast,
                 variant_name.clone(),
                 &field_list,
                 &variant.parent_enum().syntax().clone().into(),
-                visibility,
+                enum_ast.visibility(),
             );
             builder.rewrite(rewriter);
         },
     )
 }
 
-fn existing_struct_def(db: &RootDatabase, variant_name: &ast::Name, variant: &EnumVariant) -> bool {
+fn extract_field_list_if_applicable(
+    variant: &ast::Variant,
+) -> Option<Either<ast::RecordFieldList, ast::TupleFieldList>> {
+    match variant.kind() {
+        ast::StructKind::Record(field_list) if field_list.fields().next().is_some() => {
+            Some(Either::Left(field_list))
+        }
+        ast::StructKind::Tuple(field_list) if field_list.fields().count() > 1 => {
+            Some(Either::Right(field_list))
+        }
+        _ => None,
+    }
+}
+
+fn existing_definition(db: &RootDatabase, variant_name: &ast::Name, variant: &EnumVariant) -> bool {
     variant
         .parent_enum(db)
         .module(db)
         .scope(db, None)
         .into_iter()
+        .filter(|(_, def)| match def {
+            // only check type-namespace
+            hir::ScopeDef::ModuleDef(def) => matches!(def,
+                ModuleDef::Module(_) | ModuleDef::Adt(_) |
+                ModuleDef::EnumVariant(_) | ModuleDef::Trait(_) |
+                ModuleDef::TypeAlias(_) | ModuleDef::BuiltinType(_)
+            ),
+            _ => false,
+        })
         .any(|(name, _)| name == variant_name.as_name())
 }
 
@@ -133,19 +151,29 @@ fn extract_struct_def(
     rewriter: &mut SyntaxRewriter,
     enum_: &ast::Enum,
     variant_name: ast::Name,
-    variant_list: &ast::TupleFieldList,
+    field_list: &Either<ast::RecordFieldList, ast::TupleFieldList>,
     start_offset: &SyntaxElement,
     visibility: Option<ast::Visibility>,
 ) -> Option<()> {
-    let variant_list = make::tuple_field_list(
-        variant_list
-            .fields()
-            .flat_map(|field| Some(make::tuple_field(Some(make::visibility_pub()), field.ty()?))),
-    );
+    let pub_vis = Some(make::visibility_pub());
+    let field_list = match field_list {
+        Either::Left(field_list) => {
+            make::record_field_list(field_list.fields().flat_map(|field| {
+                Some(make::record_field(pub_vis.clone(), field.name()?, field.ty()?))
+            }))
+            .into()
+        }
+        Either::Right(field_list) => make::tuple_field_list(
+            field_list
+                .fields()
+                .flat_map(|field| Some(make::tuple_field(pub_vis.clone(), field.ty()?))),
+        )
+        .into(),
+    };
 
     rewriter.insert_before(
         start_offset,
-        make::struct_(visibility, variant_name, None, variant_list.into()).syntax(),
+        make::struct_(visibility, variant_name, None, field_list).syntax(),
     );
     rewriter.insert_before(start_offset, &make::tokens::blank_line());
 
@@ -156,15 +184,14 @@ fn extract_struct_def(
     Some(())
 }
 
-fn update_variant(
-    rewriter: &mut SyntaxRewriter,
-    variant_name: &ast::Name,
-    field_list: &ast::TupleFieldList,
-) -> Option<()> {
-    let (l, r): (SyntaxElement, SyntaxElement) =
-        (field_list.l_paren_token()?.into(), field_list.r_paren_token()?.into());
-    let replacement = vec![l, variant_name.syntax().clone().into(), r];
-    rewriter.replace_with_many(field_list.syntax(), replacement);
+fn update_variant(rewriter: &mut SyntaxRewriter, variant: &ast::Variant) -> Option<()> {
+    let name = variant.name()?;
+    let tuple_field = make::tuple_field(None, make::ty(name.text()));
+    let replacement = make::variant(
+        name,
+        Some(ast::FieldList::TupleFieldList(make::tuple_field_list(iter::once(tuple_field)))),
+    );
+    rewriter.replace(variant.syntax(), replacement.syntax());
     Some(())
 }
 
@@ -211,7 +238,7 @@ mod tests {
     use super::*;
 
     #[test]
-    fn test_extract_struct_several_fields() {
+    fn test_extract_struct_several_fields_tuple() {
         check_assist(
             extract_struct_from_enum_variant,
             "enum A { <|>One(u32, u32) }",
@@ -222,6 +249,41 @@ enum A { One(One) }"#,
     }
 
     #[test]
+    fn test_extract_struct_several_fields_named() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            "enum A { <|>One { foo: u32, bar: u32 } }",
+            r#"struct One{ pub foo: u32, pub bar: u32 }
+
+enum A { One(One) }"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_struct_one_field_named() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            "enum A { <|>One { foo: u32 } }",
+            r#"struct One{ pub foo: u32 }
+
+enum A { One(One) }"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_enum_variant_name_value_namespace() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            r#"const One: () = ();
+enum A { <|>One(u32, u32) }"#,
+            r#"const One: () = ();
+struct One(pub u32, pub u32);
+
+enum A { One(One) }"#,
+        );
+    }
+
+    #[test]
     fn test_extract_struct_pub_visibility() {
         check_assist(
             extract_struct_from_enum_variant,
@@ -298,7 +360,7 @@ fn another_fn() {
     fn test_extract_enum_not_applicable_if_struct_exists() {
         check_not_applicable(
             r#"struct One;
-        enum A { <|>One(u8) }"#,
+        enum A { <|>One(u8, u32) }"#,
         );
     }
 
@@ -306,4 +368,14 @@ fn another_fn() {
     fn test_extract_not_applicable_one_field() {
         check_not_applicable(r"enum A { <|>One(u32) }");
     }
+
+    #[test]
+    fn test_extract_not_applicable_no_field_tuple() {
+        check_not_applicable(r"enum A { <|>None() }");
+    }
+
+    #[test]
+    fn test_extract_not_applicable_no_field_named() {
+        check_not_applicable(r"enum A { <|>None {} }");
+    }
 }
diff --git a/crates/assists/src/handlers/flip_comma.rs b/crates/assists/src/handlers/flip_comma.rs
index 5c69db53e..64b4b1a76 100644
--- a/crates/assists/src/handlers/flip_comma.rs
+++ b/crates/assists/src/handlers/flip_comma.rs
@@ -18,7 +18,7 @@ use crate::{AssistContext, AssistId, AssistKind, Assists};
 // }
 // ```
 pub(crate) fn flip_comma(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let comma = ctx.find_token_at_offset(T![,])?;
+    let comma = ctx.find_token_syntax_at_offset(T![,])?;
     let prev = non_trivia_sibling(comma.clone().into(), Direction::Prev)?;
     let next = non_trivia_sibling(comma.clone().into(), Direction::Next)?;
 
diff --git a/crates/assists/src/handlers/flip_trait_bound.rs b/crates/assists/src/handlers/flip_trait_bound.rs
index 347e79b1d..92ee42181 100644
--- a/crates/assists/src/handlers/flip_trait_bound.rs
+++ b/crates/assists/src/handlers/flip_trait_bound.rs
@@ -20,7 +20,7 @@ use crate::{AssistContext, AssistId, AssistKind, Assists};
 pub(crate) fn flip_trait_bound(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     // We want to replicate the behavior of `flip_binexpr` by only suggesting
     // the assist when the cursor is on a `+`
-    let plus = ctx.find_token_at_offset(T![+])?;
+    let plus = ctx.find_token_syntax_at_offset(T![+])?;
 
     // Make sure we're in a `TypeBoundList`
     if ast::TypeBoundList::cast(plus.parent()).is_none() {
diff --git a/crates/assists/src/handlers/infer_function_return_type.rs b/crates/assists/src/handlers/infer_function_return_type.rs
new file mode 100644
index 000000000..520d07ae0
--- /dev/null
+++ b/crates/assists/src/handlers/infer_function_return_type.rs
@@ -0,0 +1,337 @@
+use hir::HirDisplay;
+use syntax::{ast, AstNode, TextRange, TextSize};
+use test_utils::mark;
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: infer_function_return_type
+//
+// Adds the return type to a function or closure inferred from its tail expression if it doesn't have a return
+// type specified. This assists is useable in a functions or closures tail expression or return type position.
+//
+// ```
+// fn foo() { 4<|>2i32 }
+// ```
+// ->
+// ```
+// fn foo() -> i32 { 42i32 }
+// ```
+pub(crate) fn infer_function_return_type(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let (tail_expr, builder_edit_pos, wrap_expr) = extract_tail(ctx)?;
+    let module = ctx.sema.scope(tail_expr.syntax()).module()?;
+    let ty = ctx.sema.type_of_expr(&tail_expr)?;
+    if ty.is_unit() {
+        return None;
+    }
+    let ty = ty.display_source_code(ctx.db(), module.into()).ok()?;
+
+    acc.add(
+        AssistId("infer_function_return_type", AssistKind::RefactorRewrite),
+        "Add this function's return type",
+        tail_expr.syntax().text_range(),
+        |builder| {
+            match builder_edit_pos {
+                InsertOrReplace::Insert(insert_pos) => {
+                    builder.insert(insert_pos, &format!("-> {} ", ty))
+                }
+                InsertOrReplace::Replace(text_range) => {
+                    builder.replace(text_range, &format!("-> {}", ty))
+                }
+            }
+            if wrap_expr {
+                mark::hit!(wrap_closure_non_block_expr);
+                // `|x| x` becomes `|x| -> T x` which is invalid, so wrap it in a block
+                builder.replace(tail_expr.syntax().text_range(), &format!("{{{}}}", tail_expr));
+            }
+        },
+    )
+}
+
+enum InsertOrReplace {
+    Insert(TextSize),
+    Replace(TextRange),
+}
+
+/// Check the potentially already specified return type and reject it or turn it into a builder command
+/// if allowed.
+fn ret_ty_to_action(ret_ty: Option<ast::RetType>, insert_pos: TextSize) -> Option<InsertOrReplace> {
+    match ret_ty {
+        Some(ret_ty) => match ret_ty.ty() {
+            Some(ast::Type::InferType(_)) | None => {
+                mark::hit!(existing_infer_ret_type);
+                mark::hit!(existing_infer_ret_type_closure);
+                Some(InsertOrReplace::Replace(ret_ty.syntax().text_range()))
+            }
+            _ => {
+                mark::hit!(existing_ret_type);
+                mark::hit!(existing_ret_type_closure);
+                None
+            }
+        },
+        None => Some(InsertOrReplace::Insert(insert_pos + TextSize::from(1))),
+    }
+}
+
+fn extract_tail(ctx: &AssistContext) -> Option<(ast::Expr, InsertOrReplace, bool)> {
+    let (tail_expr, return_type_range, action, wrap_expr) =
+        if let Some(closure) = ctx.find_node_at_offset::<ast::ClosureExpr>() {
+            let rpipe_pos = closure.param_list()?.syntax().last_token()?.text_range().end();
+            let action = ret_ty_to_action(closure.ret_type(), rpipe_pos)?;
+
+            let body = closure.body()?;
+            let body_start = body.syntax().first_token()?.text_range().start();
+            let (tail_expr, wrap_expr) = match body {
+                ast::Expr::BlockExpr(block) => (block.expr()?, false),
+                body => (body, true),
+            };
+
+            let ret_range = TextRange::new(rpipe_pos, body_start);
+            (tail_expr, ret_range, action, wrap_expr)
+        } else {
+            let func = ctx.find_node_at_offset::<ast::Fn>()?;
+            let rparen_pos = func.param_list()?.r_paren_token()?.text_range().end();
+            let action = ret_ty_to_action(func.ret_type(), rparen_pos)?;
+
+            let body = func.body()?;
+            let tail_expr = body.expr()?;
+
+            let ret_range_end = body.l_curly_token()?.text_range().start();
+            let ret_range = TextRange::new(rparen_pos, ret_range_end);
+            (tail_expr, ret_range, action, false)
+        };
+    let frange = ctx.frange.range;
+    if return_type_range.contains_range(frange) {
+        mark::hit!(cursor_in_ret_position);
+        mark::hit!(cursor_in_ret_position_closure);
+    } else if tail_expr.syntax().text_range().contains_range(frange) {
+        mark::hit!(cursor_on_tail);
+        mark::hit!(cursor_on_tail_closure);
+    } else {
+        return None;
+    }
+    Some((tail_expr, action, wrap_expr))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn infer_return_type_specified_inferred() {
+        mark::check!(existing_infer_ret_type);
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() -> <|>_ {
+    45
+}"#,
+            r#"fn foo() -> i32 {
+    45
+}"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type_specified_inferred_closure() {
+        mark::check!(existing_infer_ret_type_closure);
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() {
+    || -> _ {<|>45};
+}"#,
+            r#"fn foo() {
+    || -> i32 {45};
+}"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type_cursor_at_return_type_pos() {
+        mark::check!(cursor_in_ret_position);
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() <|>{
+    45
+}"#,
+            r#"fn foo() -> i32 {
+    45
+}"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type_cursor_at_return_type_pos_closure() {
+        mark::check!(cursor_in_ret_position_closure);
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() {
+    || <|>45
+}"#,
+            r#"fn foo() {
+    || -> i32 {45}
+}"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type() {
+        mark::check!(cursor_on_tail);
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() {
+    45<|>
+}"#,
+            r#"fn foo() -> i32 {
+    45
+}"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type_nested() {
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() {
+    if true {
+        3<|>
+    } else {
+        5
+    }
+}"#,
+            r#"fn foo() -> i32 {
+    if true {
+        3
+    } else {
+        5
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_ret_type_specified() {
+        mark::check!(existing_ret_type);
+        check_assist_not_applicable(
+            infer_function_return_type,
+            r#"fn foo() -> i32 {
+    ( 45<|> + 32 ) * 123
+}"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_non_tail_expr() {
+        check_assist_not_applicable(
+            infer_function_return_type,
+            r#"fn foo() {
+    let x = <|>3;
+    ( 45 + 32 ) * 123
+}"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_unit_return_type() {
+        check_assist_not_applicable(
+            infer_function_return_type,
+            r#"fn foo() {
+    (<|>)
+}"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type_closure_block() {
+        mark::check!(cursor_on_tail_closure);
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() {
+    |x: i32| {
+        x<|>
+    };
+}"#,
+            r#"fn foo() {
+    |x: i32| -> i32 {
+        x
+    };
+}"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type_closure() {
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() {
+    |x: i32| { x<|> };
+}"#,
+            r#"fn foo() {
+    |x: i32| -> i32 { x };
+}"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type_closure_wrap() {
+        mark::check!(wrap_closure_non_block_expr);
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() {
+    |x: i32| x<|>;
+}"#,
+            r#"fn foo() {
+    |x: i32| -> i32 {x};
+}"#,
+        );
+    }
+
+    #[test]
+    fn infer_return_type_nested_closure() {
+        check_assist(
+            infer_function_return_type,
+            r#"fn foo() {
+    || {
+        if true {
+            3<|>
+        } else {
+            5
+        }
+    }
+}"#,
+            r#"fn foo() {
+    || -> i32 {
+        if true {
+            3
+        } else {
+            5
+        }
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_ret_type_specified_closure() {
+        mark::check!(existing_ret_type_closure);
+        check_assist_not_applicable(
+            infer_function_return_type,
+            r#"fn foo() {
+    || -> i32 { 3<|> }
+}"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_non_tail_expr_closure() {
+        check_assist_not_applicable(
+            infer_function_return_type,
+            r#"fn foo() {
+    || -> i32 {
+        let x = 3<|>;
+        6
+    }
+}"#,
+        );
+    }
+}
diff --git a/crates/assists/src/handlers/introduce_named_lifetime.rs b/crates/assists/src/handlers/introduce_named_lifetime.rs
index 5f623e5f7..4cc8dae65 100644
--- a/crates/assists/src/handlers/introduce_named_lifetime.rs
+++ b/crates/assists/src/handlers/introduce_named_lifetime.rs
@@ -36,7 +36,7 @@ static ASSIST_LABEL: &str = "Introduce named lifetime";
 // FIXME: should also add support for the case fun(f: &Foo) -> &<|>Foo
 pub(crate) fn introduce_named_lifetime(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let lifetime_token = ctx
-        .find_token_at_offset(SyntaxKind::LIFETIME)
+        .find_token_syntax_at_offset(SyntaxKind::LIFETIME)
         .filter(|lifetime| lifetime.text() == "'_")?;
     if let Some(fn_def) = lifetime_token.ancestors().find_map(ast::Fn::cast) {
         generate_fn_def_assist(acc, &fn_def, lifetime_token.text_range())
diff --git a/crates/assists/src/handlers/invert_if.rs b/crates/assists/src/handlers/invert_if.rs
index 461fcf862..ea722b91b 100644
--- a/crates/assists/src/handlers/invert_if.rs
+++ b/crates/assists/src/handlers/invert_if.rs
@@ -29,7 +29,7 @@ use crate::{
 // ```
 
 pub(crate) fn invert_if(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let if_keyword = ctx.find_token_at_offset(T![if])?;
+    let if_keyword = ctx.find_token_syntax_at_offset(T![if])?;
     let expr = ast::IfExpr::cast(if_keyword.parent())?;
     let if_range = if_keyword.text_range();
     let cursor_in_range = if_range.contains_range(ctx.frange.range);
diff --git a/crates/assists/src/handlers/raw_string.rs b/crates/assists/src/handlers/raw_string.rs
index 9ddd116e0..4c759cc25 100644
--- a/crates/assists/src/handlers/raw_string.rs
+++ b/crates/assists/src/handlers/raw_string.rs
@@ -1,11 +1,6 @@
 use std::borrow::Cow;
 
-use syntax::{
-    ast::{self, HasQuotes, HasStringValue},
-    AstToken,
-    SyntaxKind::{RAW_STRING, STRING},
-    TextRange, TextSize,
-};
+use syntax::{ast, AstToken, TextRange, TextSize};
 use test_utils::mark;
 
 use crate::{AssistContext, AssistId, AssistKind, Assists};
@@ -26,7 +21,10 @@ use crate::{AssistContext, AssistId, AssistKind, Assists};
 // }
 // ```
 pub(crate) fn make_raw_string(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let token = ctx.find_token_at_offset(STRING).and_then(ast::String::cast)?;
+    let token = ctx.find_token_at_offset::<ast::String>()?;
+    if token.is_raw() {
+        return None;
+    }
     let value = token.value()?;
     let target = token.syntax().text_range();
     acc.add(
@@ -65,7 +63,10 @@ pub(crate) fn make_raw_string(acc: &mut Assists, ctx: &AssistContext) -> Option<
 // }
 // ```
 pub(crate) fn make_usual_string(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let token = ctx.find_token_at_offset(RAW_STRING).and_then(ast::RawString::cast)?;
+    let token = ctx.find_token_at_offset::<ast::String>()?;
+    if !token.is_raw() {
+        return None;
+    }
     let value = token.value()?;
     let target = token.syntax().text_range();
     acc.add(
@@ -104,11 +105,15 @@ pub(crate) fn make_usual_string(acc: &mut Assists, ctx: &AssistContext) -> Optio
 // }
 // ```
 pub(crate) fn add_hash(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let token = ctx.find_token_at_offset(RAW_STRING)?;
-    let target = token.text_range();
+    let token = ctx.find_token_at_offset::<ast::String>()?;
+    if !token.is_raw() {
+        return None;
+    }
+    let text_range = token.syntax().text_range();
+    let target = text_range;
     acc.add(AssistId("add_hash", AssistKind::Refactor), "Add #", target, |edit| {
-        edit.insert(token.text_range().start() + TextSize::of('r'), "#");
-        edit.insert(token.text_range().end(), "#");
+        edit.insert(text_range.start() + TextSize::of('r'), "#");
+        edit.insert(text_range.end(), "#");
     })
 }
 
@@ -128,7 +133,10 @@ pub(crate) fn add_hash(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
 // }
 // ```
 pub(crate) fn remove_hash(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let token = ctx.find_token_at_offset(RAW_STRING).and_then(ast::RawString::cast)?;
+    let token = ctx.find_token_at_offset::<ast::String>()?;
+    if !token.is_raw() {
+        return None;
+    }
 
     let text = token.text().as_str();
     if !text.starts_with("r#") && text.ends_with('#') {
diff --git a/crates/assists/src/handlers/remove_mut.rs b/crates/assists/src/handlers/remove_mut.rs
index 44f41daa9..575b271f7 100644
--- a/crates/assists/src/handlers/remove_mut.rs
+++ b/crates/assists/src/handlers/remove_mut.rs
@@ -18,7 +18,7 @@ use crate::{AssistContext, AssistId, AssistKind, Assists};
 // }
 // ```
 pub(crate) fn remove_mut(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let mut_token = ctx.find_token_at_offset(T![mut])?;
+    let mut_token = ctx.find_token_syntax_at_offset(T![mut])?;
     let delete_from = mut_token.text_range().start();
     let delete_to = match mut_token.next_token() {
         Some(it) if it.kind() == SyntaxKind::WHITESPACE => it.text_range().end(),
diff --git a/crates/assists/src/handlers/reorder_fields.rs b/crates/assists/src/handlers/reorder_fields.rs
index 527f457a7..7c0f0f44e 100644
--- a/crates/assists/src/handlers/reorder_fields.rs
+++ b/crates/assists/src/handlers/reorder_fields.rs
@@ -47,9 +47,11 @@ fn reorder<R: AstNode>(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
         "Reorder record fields",
         target,
         |edit| {
+            let mut rewriter = algo::SyntaxRewriter::default();
             for (old, new) in fields.iter().zip(&sorted_fields) {
-                algo::diff(old, new).into_text_edit(edit.text_edit_builder());
+                rewriter.replace(old, new);
             }
+            edit.rewrite(rewriter);
         },
     )
 }
diff --git a/crates/assists/src/handlers/replace_let_with_if_let.rs b/crates/assists/src/handlers/replace_let_with_if_let.rs
index a5bcbda24..69d3b08d3 100644
--- a/crates/assists/src/handlers/replace_let_with_if_let.rs
+++ b/crates/assists/src/handlers/replace_let_with_if_let.rs
@@ -37,7 +37,7 @@ use ide_db::ty_filter::TryEnum;
 // fn compute() -> Option<i32> { None }
 // ```
 pub(crate) fn replace_let_with_if_let(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let let_kw = ctx.find_token_at_offset(T![let])?;
+    let let_kw = ctx.find_token_syntax_at_offset(T![let])?;
     let let_stmt = let_kw.ancestors().find_map(ast::LetStmt::cast)?;
     let init = let_stmt.initializer()?;
     let original_pat = let_stmt.pat()?;
diff --git a/crates/assists/src/handlers/replace_string_with_char.rs b/crates/assists/src/handlers/replace_string_with_char.rs
index 4ca87a8ec..b4b898846 100644
--- a/crates/assists/src/handlers/replace_string_with_char.rs
+++ b/crates/assists/src/handlers/replace_string_with_char.rs
@@ -1,8 +1,4 @@
-use syntax::{
-    ast::{self, HasStringValue},
-    AstToken,
-    SyntaxKind::STRING,
-};
+use syntax::{ast, AstToken, SyntaxKind::STRING};
 
 use crate::{AssistContext, AssistId, AssistKind, Assists};
 
@@ -22,7 +18,7 @@ use crate::{AssistContext, AssistId, AssistKind, Assists};
 // }
 // ```
 pub(crate) fn replace_string_with_char(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let token = ctx.find_token_at_offset(STRING).and_then(ast::String::cast)?;
+    let token = ctx.find_token_syntax_at_offset(STRING).and_then(ast::String::cast)?;
     let value = token.value()?;
     let target = token.syntax().text_range();
 
diff --git a/crates/assists/src/handlers/split_import.rs b/crates/assists/src/handlers/split_import.rs
index 15e67eaa1..ef1f6b8a1 100644
--- a/crates/assists/src/handlers/split_import.rs
+++ b/crates/assists/src/handlers/split_import.rs
@@ -16,7 +16,7 @@ use crate::{AssistContext, AssistId, AssistKind, Assists};
 // use std::{collections::HashMap};
 // ```
 pub(crate) fn split_import(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
-    let colon_colon = ctx.find_token_at_offset(T![::])?;
+    let colon_colon = ctx.find_token_syntax_at_offset(T![::])?;
     let path = ast::Path::cast(colon_colon.parent())?.qualifier()?;
     let top_path = successors(Some(path.clone()), |it| it.parent_path()).last()?;
 
diff --git a/crates/assists/src/handlers/unwrap_block.rs b/crates/assists/src/handlers/unwrap_block.rs
index 3851aeb3e..36ef871b9 100644
--- a/crates/assists/src/handlers/unwrap_block.rs
+++ b/crates/assists/src/handlers/unwrap_block.rs
@@ -29,7 +29,7 @@ pub(crate) fn unwrap_block(acc: &mut Assists, ctx: &AssistContext) -> Option<()>
     let assist_id = AssistId("unwrap_block", AssistKind::RefactorRewrite);
     let assist_label = "Unwrap block";
 
-    let l_curly_token = ctx.find_token_at_offset(T!['{'])?;
+    let l_curly_token = ctx.find_token_syntax_at_offset(T!['{'])?;
     let mut block = ast::BlockExpr::cast(l_curly_token.parent())?;
     let mut parent = block.syntax().parent()?;
     if ast::MatchArm::can_cast(parent.kind()) {
diff --git a/crates/assists/src/lib.rs b/crates/assists/src/lib.rs
index b804e495d..af88b3437 100644
--- a/crates/assists/src/lib.rs
+++ b/crates/assists/src/lib.rs
@@ -143,6 +143,7 @@ mod handlers {
     mod generate_function;
     mod generate_impl;
     mod generate_new;
+    mod infer_function_return_type;
     mod inline_local_variable;
     mod introduce_named_lifetime;
     mod invert_if;
@@ -190,6 +191,7 @@ mod handlers {
             generate_function::generate_function,
             generate_impl::generate_impl,
             generate_new::generate_new,
+            infer_function_return_type::infer_function_return_type,
             inline_local_variable::inline_local_variable,
             introduce_named_lifetime::introduce_named_lifetime,
             invert_if::invert_if,
diff --git a/crates/assists/src/tests/generated.rs b/crates/assists/src/tests/generated.rs
index acbf5b652..168e1626a 100644
--- a/crates/assists/src/tests/generated.rs
+++ b/crates/assists/src/tests/generated.rs
@@ -506,6 +506,19 @@ impl<T: Clone> Ctx<T> {
 }
 
 #[test]
+fn doctest_infer_function_return_type() {
+    check_doc_test(
+        "infer_function_return_type",
+        r#####"
+fn foo() { 4<|>2i32 }
+"#####,
+        r#####"
+fn foo() -> i32 { 42i32 }
+"#####,
+    )
+}
+
+#[test]
 fn doctest_inline_local_variable() {
     check_doc_test(
         "inline_local_variable",
diff --git a/crates/assists/src/utils.rs b/crates/assists/src/utils.rs
index 56f925ee6..7071fe96b 100644
--- a/crates/assists/src/utils.rs
+++ b/crates/assists/src/utils.rs
@@ -4,17 +4,22 @@ pub(crate) mod import_assets;
 
 use std::ops;
 
-use hir::{Crate, Enum, Module, ScopeDef, Semantics, Trait};
+use hir::{Crate, Enum, HasSource, Module, ScopeDef, Semantics, Trait};
 use ide_db::RootDatabase;
 use itertools::Itertools;
 use syntax::{
-    ast::{self, make, ArgListOwner},
+    ast::edit::AstNodeEdit,
+    ast::NameOwner,
+    ast::{self, edit, make, ArgListOwner},
     AstNode, Direction,
     SyntaxKind::*,
     SyntaxNode, TextSize, T,
 };
 
-use crate::assist_config::SnippetCap;
+use crate::{
+    assist_config::SnippetCap,
+    ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
+};
 
 pub use insert_use::MergeBehaviour;
 pub(crate) use insert_use::{insert_use, ImportScope};
@@ -77,6 +82,87 @@ pub fn extract_trivial_expression(block: &ast::BlockExpr) -> Option<ast::Expr> {
     None
 }
 
+#[derive(Copy, Clone, PartialEq)]
+pub enum DefaultMethods {
+    Only,
+    No,
+}
+
+pub fn filter_assoc_items(
+    db: &RootDatabase,
+    items: &[hir::AssocItem],
+    default_methods: DefaultMethods,
+) -> Vec<ast::AssocItem> {
+    fn has_def_name(item: &ast::AssocItem) -> bool {
+        match item {
+            ast::AssocItem::Fn(def) => def.name(),
+            ast::AssocItem::TypeAlias(def) => def.name(),
+            ast::AssocItem::Const(def) => def.name(),
+            ast::AssocItem::MacroCall(_) => None,
+        }
+        .is_some()
+    };
+
+    items
+        .iter()
+        .map(|i| match i {
+            hir::AssocItem::Function(i) => ast::AssocItem::Fn(i.source(db).value),
+            hir::AssocItem::TypeAlias(i) => ast::AssocItem::TypeAlias(i.source(db).value),
+            hir::AssocItem::Const(i) => ast::AssocItem::Const(i.source(db).value),
+        })
+        .filter(has_def_name)
+        .filter(|it| match it {
+            ast::AssocItem::Fn(def) => matches!(
+                (default_methods, def.body()),
+                (DefaultMethods::Only, Some(_)) | (DefaultMethods::No, None)
+            ),
+            _ => default_methods == DefaultMethods::No,
+        })
+        .collect::<Vec<_>>()
+}
+
+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,
+    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()));
+
+    let items = items
+        .into_iter()
+        .map(|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 => {
+                let body =
+                    make::block_expr(None, Some(make::expr_todo())).indent(edit::IndentLevel(1));
+                fn_def.with_body(body)
+            }
+        }
+    }
+}
+
 #[derive(Clone, Copy, Debug)]
 pub(crate) enum Cursor<'a> {
     Replace(&'a SyntaxNode),