From 265707857379e12490a344ad7cb70af5edec59e8 Mon Sep 17 00:00:00 2001
From: maxwase <max.vvase@gmail.com>
Date: Sat, 18 May 2024 19:37:04 +0300
Subject: [PATCH 1/3] Add toggle_async_sugar assist code action

---
 .../src/handlers/toggle_async_sugar.rs        | 460 ++++++++++++++++++
 crates/ide-assists/src/lib.rs                 |   2 +
 crates/ide-assists/src/tests/generated.rs     |  17 +
 crates/ide-db/src/famous_defs.rs              |   4 +
 4 files changed, 483 insertions(+)
 create mode 100644 crates/ide-assists/src/handlers/toggle_async_sugar.rs

diff --git a/crates/ide-assists/src/handlers/toggle_async_sugar.rs b/crates/ide-assists/src/handlers/toggle_async_sugar.rs
new file mode 100644
index 0000000000..ea127d65e5
--- /dev/null
+++ b/crates/ide-assists/src/handlers/toggle_async_sugar.rs
@@ -0,0 +1,460 @@
+use ide_db::{
+    assists::{AssistId, AssistKind},
+    famous_defs::FamousDefs,
+};
+use syntax::{
+    ast::{self, HasVisibility},
+    AstNode, NodeOrToken, SyntaxKind, SyntaxNode, SyntaxToken, TextRange,
+};
+
+use crate::{AssistContext, Assists};
+
+// Assist: toggle_async_sugar
+//
+// Rewrites asynchronous function into `impl Future` and back.
+// This action does not touch the function body and therefore `async { 0 }`
+// block does not transform to just `0`.
+//
+// ```
+// pub async f$0n foo() -> usize {
+//     0
+// }
+// ```
+// ->
+// ```
+// pub fn foo() -> impl Future<Output = usize> {
+//     0
+// }
+// ```
+pub(crate) fn toggle_async_sugar(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let function: ast::Fn = ctx.find_node_at_offset()?;
+    match (function.async_token(), function.ret_type()) {
+        // async function returning futures cannot be flattened
+        // const async is not yet supported
+        (None, Some(ret_type)) if function.const_token().is_none() => {
+            add_async(acc, ctx, function, ret_type)
+        }
+        (Some(async_token), ret_type) => remove_async(function, ret_type, acc, async_token),
+        _ => None,
+    }
+}
+
+fn add_async(
+    acc: &mut Assists,
+    ctx: &AssistContext<'_>,
+    function: ast::Fn,
+    ret_type: ast::RetType,
+) -> Option<()> {
+    let ast::Type::ImplTraitType(return_impl_trait) = ret_type.ty()? else {
+        return None;
+    };
+
+    let main_trait_path = return_impl_trait
+        .type_bound_list()?
+        .bounds()
+        .filter_map(|bound| match bound.ty() {
+            Some(ast::Type::PathType(trait_path)) => trait_path.path(),
+            _ => None,
+        })
+        .next()?;
+
+    let trait_type = ctx.sema.resolve_trait(&main_trait_path)?;
+    let scope = ctx.sema.scope(main_trait_path.syntax())?;
+    if trait_type != FamousDefs(&ctx.sema, scope.krate()).core_future_Future()? {
+        return None;
+    }
+    let future_output = unwrap_future_output(main_trait_path)?;
+
+    acc.add(
+        AssistId("toggle_async_sugar", AssistKind::RefactorRewrite),
+        "Convert `impl Future` into async",
+        function.syntax().text_range(),
+        |builder| {
+            match future_output {
+                ast::Type::TupleType(_) => {
+                    let mut ret_type_range = ret_type.syntax().text_range();
+
+                    // find leftover whitespace
+                    let whitespace_range = function
+                        .param_list()
+                        .as_ref()
+                        .map(|params| NodeOrToken::Node(params.syntax()))
+                        .and_then(following_whitespace);
+
+                    if let Some(whitespace_range) = whitespace_range {
+                        ret_type_range =
+                            TextRange::new(whitespace_range.start(), ret_type_range.end());
+                    }
+
+                    builder.delete(ret_type_range);
+                }
+                _ => {
+                    builder.replace(
+                        return_impl_trait.syntax().text_range(),
+                        future_output.syntax().text(),
+                    );
+                }
+            }
+
+            let (place_for_async, async_kw) = match function.visibility() {
+                Some(vis) => (vis.syntax().text_range().end(), " async"),
+                None => (function.syntax().text_range().start(), "async "),
+            };
+            builder.insert(place_for_async, async_kw);
+        },
+    )
+}
+
+fn remove_async(
+    function: ast::Fn,
+    ret_type: Option<ast::RetType>,
+    acc: &mut Assists,
+    async_token: SyntaxToken,
+) -> Option<()> {
+    let rparen = function.param_list()?.r_paren_token()?;
+    let return_type = match ret_type {
+        // unable to get a `ty` makes the action unapplicable
+        Some(ret_type) => Some(ret_type.ty()?),
+        // No type means `-> ()`
+        None => None,
+    };
+
+    acc.add(
+        AssistId("toggle_async_sugar", AssistKind::RefactorRewrite),
+        "Convert async into `impl Future`",
+        function.syntax().text_range(),
+        |builder| {
+            let mut async_range = async_token.text_range();
+
+            if let Some(whitespace_range) = following_whitespace(NodeOrToken::Token(async_token)) {
+                async_range = TextRange::new(async_range.start(), whitespace_range.end());
+            }
+            builder.delete(async_range);
+
+            match return_type {
+                Some(ret_type) => builder.replace(
+                    ret_type.syntax().text_range(),
+                    format!("impl Future<Output = {ret_type}>"),
+                ),
+                None => builder.insert(rparen.text_range().end(), " -> impl Future<Output = ()>"),
+            }
+        },
+    )
+}
+
+fn unwrap_future_output(path: ast::Path) -> Option<ast::Type> {
+    let future_trait = path.segments().last()?;
+    let assoc_list = future_trait.generic_arg_list()?;
+    let future_assoc = assoc_list.generic_args().next()?;
+    match future_assoc {
+        ast::GenericArg::AssocTypeArg(output_type) => output_type.ty(),
+        _ => None,
+    }
+}
+
+fn following_whitespace(nt: NodeOrToken<&SyntaxNode, SyntaxToken>) -> Option<TextRange> {
+    let next_token = match nt {
+        NodeOrToken::Node(node) => node.next_sibling_or_token(),
+        NodeOrToken::Token(token) => token.next_sibling_or_token(),
+    }?;
+    (next_token.kind() == SyntaxKind::WHITESPACE).then_some(next_token.text_range())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    #[test]
+    fn sugar_with_use() {
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    use core::future::Future;
+    f$0n foo() -> impl Future<Output = ()> {
+        todo!()
+    }
+    "#,
+            r#"
+    use core::future::Future;
+    async fn foo() {
+        todo!()
+    }
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    use core::future::Future;
+    f$0n foo() -> impl Future<Output = usize> {
+        todo!()
+    }
+    "#,
+            r#"
+    use core::future::Future;
+    async fn foo() -> usize {
+        todo!()
+    }
+    "#,
+        );
+    }
+
+    #[test]
+    fn desugar_with_use() {
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    use core::future::Future;
+    async f$0n foo() {
+        todo!()
+    }
+    "#,
+            r#"
+    use core::future::Future;
+    fn foo() -> impl Future<Output = ()> {
+        todo!()
+    }
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    use core::future::Future;
+    async f$0n foo() -> usize {
+        todo!()
+    }
+    "#,
+            r#"
+    use core::future::Future;
+    fn foo() -> impl Future<Output = usize> {
+        todo!()
+    }
+    "#,
+        );
+    }
+
+    #[test]
+    fn sugar_without_use() {
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    f$0n foo() -> impl core::future::Future<Output = ()> {
+        todo!()
+    }
+    "#,
+            r#"
+    async fn foo() {
+        todo!()
+    }
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    f$0n foo() -> impl core::future::Future<Output = usize> {
+        todo!()
+    }
+    "#,
+            r#"
+    async fn foo() -> usize {
+        todo!()
+    }
+    "#,
+        );
+    }
+
+    #[test]
+    fn desugar_without_use() {
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    async f$0n foo() {
+        todo!()
+    }
+    "#,
+            r#"
+    fn foo() -> impl Future<Output = ()> {
+        todo!()
+    }
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    async f$0n foo() -> usize {
+        todo!()
+    }
+    "#,
+            r#"
+    fn foo() -> impl Future<Output = usize> {
+        todo!()
+    }
+    "#,
+        );
+    }
+
+    #[test]
+    fn sugar_not_applicable() {
+        check_assist_not_applicable(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    trait Future {
+        type Output;
+    }
+    f$0n foo() -> impl Future<Output = ()> {
+        todo!()
+    }
+    "#,
+        );
+
+        check_assist_not_applicable(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    trait Future {
+        type Output;
+    }
+    f$0n foo() -> impl Future<Output = usize> {
+        todo!()
+    }
+    "#,
+        );
+    }
+
+    #[test]
+    fn sugar_definition_with_use() {
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    use core::future::Future;
+    f$0n foo() -> impl Future<Output = ()>;
+    "#,
+            r#"
+    use core::future::Future;
+    async fn foo();
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    use core::future::Future;
+    f$0n foo() -> impl Future<Output = usize>;
+    "#,
+            r#"
+    use core::future::Future;
+    async fn foo() -> usize;
+    "#,
+        );
+    }
+
+    #[test]
+    fn sugar_definition_without_use() {
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    f$0n foo() -> impl core::future::Future<Output = ()>;
+    "#,
+            r#"
+    async fn foo();
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    f$0n foo() -> impl core::future::Future<Output = usize>;
+    "#,
+            r#"
+    async fn foo() -> usize;
+    "#,
+        );
+    }
+
+    #[test]
+    fn sugar_with_modifiers() {
+        check_assist_not_applicable(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    const f$0n foo() -> impl core::future::Future<Output = ()>;
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+            //- minicore: future
+            pub(crate) unsafe f$0n foo() -> impl core::future::Future<Output = usize>;
+        "#,
+            r#"
+            pub(crate) async unsafe fn foo() -> usize;
+        "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    unsafe f$0n foo() -> impl core::future::Future<Output = ()>;
+    "#,
+            r#"
+    async unsafe fn foo();
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    unsafe extern "C" f$0n foo() -> impl core::future::Future<Output = ()>;
+    "#,
+            r#"
+    async unsafe extern "C" fn foo();
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    f$0n foo<T>() -> impl core::future::Future<Output = T>;
+    "#,
+            r#"
+    async fn foo<T>() -> T;
+    "#,
+        );
+
+        check_assist(
+            toggle_async_sugar,
+            r#"
+    //- minicore: future
+    f$0n foo<T>() -> impl core::future::Future<Output = T>
+    where
+        T: Sized;
+    "#,
+            r#"
+    async fn foo<T>() -> T
+    where
+        T: Sized;
+    "#,
+        );
+    }
+}
diff --git a/crates/ide-assists/src/lib.rs b/crates/ide-assists/src/lib.rs
index 0df5e913a5..d26ac23099 100644
--- a/crates/ide-assists/src/lib.rs
+++ b/crates/ide-assists/src/lib.rs
@@ -209,6 +209,7 @@ mod handlers {
     mod sort_items;
     mod split_import;
     mod term_search;
+    mod toggle_async_sugar;
     mod toggle_ignore;
     mod unmerge_match_arm;
     mod unmerge_use;
@@ -238,6 +239,7 @@ mod handlers {
             change_visibility::change_visibility,
             convert_bool_then::convert_bool_then_to_if,
             convert_bool_then::convert_if_to_bool_then,
+            toggle_async_sugar::toggle_async_sugar,
             convert_comment_block::convert_comment_block,
             convert_from_to_tryfrom::convert_from_to_tryfrom,
             convert_integer_literal::convert_integer_literal,
diff --git a/crates/ide-assists/src/tests/generated.rs b/crates/ide-assists/src/tests/generated.rs
index 937e78f8d7..8e0d1bd667 100644
--- a/crates/ide-assists/src/tests/generated.rs
+++ b/crates/ide-assists/src/tests/generated.rs
@@ -3020,6 +3020,23 @@ use std::{collections::HashMap};
     )
 }
 
+#[test]
+fn doctest_toggle_async_sugar() {
+    check_doc_test(
+        "toggle_async_sugar",
+        r#####"
+pub async f$0n foo() -> usize {
+    0
+}
+"#####,
+        r#####"
+pub fn foo() -> impl Future<Output = usize> {
+    0
+}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_toggle_ignore() {
     check_doc_test(
diff --git a/crates/ide-db/src/famous_defs.rs b/crates/ide-db/src/famous_defs.rs
index 3106772e63..e445e9fb68 100644
--- a/crates/ide-db/src/famous_defs.rs
+++ b/crates/ide-db/src/famous_defs.rs
@@ -106,6 +106,10 @@ impl FamousDefs<'_, '_> {
         self.find_trait("core:marker:Copy")
     }
 
+    pub fn core_future_Future(&self) -> Option<Trait> {
+        self.find_trait("core:future:Future")
+    }
+
     pub fn core_macros_builtin_derive(&self) -> Option<Macro> {
         self.find_macro("core:macros:builtin:derive")
     }

From 624f99b4b9f66cd056fc07a83fbb287fd4960aa5 Mon Sep 17 00:00:00 2001
From: maxwase <max.vvase@gmail.com>
Date: Fri, 24 May 2024 01:10:18 +0300
Subject: [PATCH 2/3] Review fixes: Split into 2, check tuple fields

---
 .../src/handlers/toggle_async_sugar.rs        | 161 ++++++++++++------
 crates/ide-assists/src/lib.rs                 |   3 +-
 crates/ide-assists/src/tests/generated.rs     |  30 +++-
 3 files changed, 137 insertions(+), 57 deletions(-)

diff --git a/crates/ide-assists/src/handlers/toggle_async_sugar.rs b/crates/ide-assists/src/handlers/toggle_async_sugar.rs
index ea127d65e5..356e1d50ae 100644
--- a/crates/ide-assists/src/handlers/toggle_async_sugar.rs
+++ b/crates/ide-assists/src/handlers/toggle_async_sugar.rs
@@ -9,42 +9,38 @@ use syntax::{
 
 use crate::{AssistContext, Assists};
 
-// Assist: toggle_async_sugar
+// Assist: sugar_impl_future_into_async
 //
-// Rewrites asynchronous function into `impl Future` and back.
+// Rewrites asynchronous function from `impl Future` to `async fn`.
 // This action does not touch the function body and therefore `async { 0 }`
 // block does not transform to just `0`.
 //
 // ```
-// pub async f$0n foo() -> usize {
-//     0
+// # //- minicore: future
+// pub f$0n foo() -> impl core::future::Future<Output = usize> {
+//     async { 0 }
 // }
 // ```
 // ->
 // ```
-// pub fn foo() -> impl Future<Output = usize> {
-//     0
+// pub async fn foo() -> usize {
+//     async { 0 }
 // }
 // ```
-pub(crate) fn toggle_async_sugar(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
-    let function: ast::Fn = ctx.find_node_at_offset()?;
-    match (function.async_token(), function.ret_type()) {
-        // async function returning futures cannot be flattened
-        // const async is not yet supported
-        (None, Some(ret_type)) if function.const_token().is_none() => {
-            add_async(acc, ctx, function, ret_type)
-        }
-        (Some(async_token), ret_type) => remove_async(function, ret_type, acc, async_token),
-        _ => None,
-    }
-}
-
-fn add_async(
+pub(crate) fn sugar_impl_future_into_async(
     acc: &mut Assists,
     ctx: &AssistContext<'_>,
-    function: ast::Fn,
-    ret_type: ast::RetType,
 ) -> Option<()> {
+    let function: ast::Fn = ctx.find_node_at_offset()?;
+    if function.async_token().is_some() {
+        return None;
+    }
+
+    let ret_type = function.ret_type()?;
+    if function.const_token().is_some() {
+        return None;
+    }
+
     let ast::Type::ImplTraitType(return_impl_trait) = ret_type.ty()? else {
         return None;
     };
@@ -66,12 +62,12 @@ fn add_async(
     let future_output = unwrap_future_output(main_trait_path)?;
 
     acc.add(
-        AssistId("toggle_async_sugar", AssistKind::RefactorRewrite),
+        AssistId("sugar_impl_future_into_async", AssistKind::RefactorRewrite),
         "Convert `impl Future` into async",
         function.syntax().text_range(),
         |builder| {
             match future_output {
-                ast::Type::TupleType(_) => {
+                ast::Type::TupleType(t) if t.fields().next().is_none() => {
                     let mut ret_type_range = ret_type.syntax().text_range();
 
                     // find leftover whitespace
@@ -105,14 +101,32 @@ fn add_async(
     )
 }
 
-fn remove_async(
-    function: ast::Fn,
-    ret_type: Option<ast::RetType>,
+// Assist: desugar_async_into_impl_future
+//
+// Rewrites asynchronous function from `async fn` to `impl Future`.
+// This action does not touch the function body and therefore `0`
+// block does not transform to `async { 0 }`.
+//
+// ```
+// pub async f$0n foo() -> usize {
+//     0
+// }
+// ```
+// ->
+// ```
+// pub fn foo() -> impl Future<Output = usize> {
+//     0
+// }
+// ```
+pub(crate) fn desugar_async_into_impl_future(
     acc: &mut Assists,
-    async_token: SyntaxToken,
+    ctx: &AssistContext<'_>,
 ) -> Option<()> {
+    let function: ast::Fn = ctx.find_node_at_offset()?;
+    let async_token = function.async_token()?;
+
     let rparen = function.param_list()?.r_paren_token()?;
-    let return_type = match ret_type {
+    let return_type = match function.ret_type() {
         // unable to get a `ty` makes the action unapplicable
         Some(ret_type) => Some(ret_type.ty()?),
         // No type means `-> ()`
@@ -120,7 +134,7 @@ fn remove_async(
     };
 
     acc.add(
-        AssistId("toggle_async_sugar", AssistKind::RefactorRewrite),
+        AssistId("desugar_async_into_impl_future", AssistKind::RefactorRewrite),
         "Convert async into `impl Future`",
         function.syntax().text_range(),
         |builder| {
@@ -168,7 +182,7 @@ mod tests {
     #[test]
     fn sugar_with_use() {
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     use core::future::Future;
@@ -185,7 +199,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     use core::future::Future;
@@ -205,7 +219,7 @@ mod tests {
     #[test]
     fn desugar_with_use() {
         check_assist(
-            toggle_async_sugar,
+            desugar_async_into_impl_future,
             r#"
     //- minicore: future
     use core::future::Future;
@@ -222,7 +236,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            desugar_async_into_impl_future,
             r#"
     //- minicore: future
     use core::future::Future;
@@ -242,7 +256,7 @@ mod tests {
     #[test]
     fn sugar_without_use() {
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     f$0n foo() -> impl core::future::Future<Output = ()> {
@@ -257,7 +271,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     f$0n foo() -> impl core::future::Future<Output = usize> {
@@ -275,7 +289,7 @@ mod tests {
     #[test]
     fn desugar_without_use() {
         check_assist(
-            toggle_async_sugar,
+            desugar_async_into_impl_future,
             r#"
     //- minicore: future
     async f$0n foo() {
@@ -290,7 +304,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            desugar_async_into_impl_future,
             r#"
     //- minicore: future
     async f$0n foo() -> usize {
@@ -308,7 +322,7 @@ mod tests {
     #[test]
     fn sugar_not_applicable() {
         check_assist_not_applicable(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     trait Future {
@@ -321,7 +335,7 @@ mod tests {
         );
 
         check_assist_not_applicable(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     trait Future {
@@ -337,7 +351,7 @@ mod tests {
     #[test]
     fn sugar_definition_with_use() {
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     use core::future::Future;
@@ -350,7 +364,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     use core::future::Future;
@@ -366,7 +380,7 @@ mod tests {
     #[test]
     fn sugar_definition_without_use() {
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     f$0n foo() -> impl core::future::Future<Output = ()>;
@@ -377,7 +391,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     f$0n foo() -> impl core::future::Future<Output = usize>;
@@ -388,10 +402,57 @@ mod tests {
         );
     }
 
+    #[test]
+    fn sugar_more_types() {
+        check_assist(
+            sugar_impl_future_into_async,
+            r#"
+    //- minicore: future
+    f$0n foo() -> impl core::future::Future<Output = ()> + Send + Sync;
+    "#,
+            r#"
+    async fn foo();
+    "#,
+        );
+
+        check_assist(
+            sugar_impl_future_into_async,
+            r#"
+    //- minicore: future
+    f$0n foo() -> impl core::future::Future<Output = usize> + Debug;
+    "#,
+            r#"
+    async fn foo() -> usize;
+    "#,
+        );
+
+        check_assist(
+            sugar_impl_future_into_async,
+            r#"
+    //- minicore: future
+    f$0n foo() -> impl core::future::Future<Output = (usize)> + Debug;
+    "#,
+            r#"
+    async fn foo() -> (usize);
+    "#,
+        );
+
+        check_assist(
+            sugar_impl_future_into_async,
+            r#"
+    //- minicore: future
+    f$0n foo() -> impl core::future::Future<Output = (usize, usize)> + Debug;
+    "#,
+            r#"
+    async fn foo() -> (usize, usize);
+    "#,
+        );
+    }
+
     #[test]
     fn sugar_with_modifiers() {
         check_assist_not_applicable(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     const f$0n foo() -> impl core::future::Future<Output = ()>;
@@ -399,7 +460,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
             //- minicore: future
             pub(crate) unsafe f$0n foo() -> impl core::future::Future<Output = usize>;
@@ -410,7 +471,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     unsafe f$0n foo() -> impl core::future::Future<Output = ()>;
@@ -421,7 +482,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     unsafe extern "C" f$0n foo() -> impl core::future::Future<Output = ()>;
@@ -432,7 +493,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     f$0n foo<T>() -> impl core::future::Future<Output = T>;
@@ -443,7 +504,7 @@ mod tests {
         );
 
         check_assist(
-            toggle_async_sugar,
+            sugar_impl_future_into_async,
             r#"
     //- minicore: future
     f$0n foo<T>() -> impl core::future::Future<Output = T>
diff --git a/crates/ide-assists/src/lib.rs b/crates/ide-assists/src/lib.rs
index d26ac23099..34ef341c44 100644
--- a/crates/ide-assists/src/lib.rs
+++ b/crates/ide-assists/src/lib.rs
@@ -239,7 +239,8 @@ mod handlers {
             change_visibility::change_visibility,
             convert_bool_then::convert_bool_then_to_if,
             convert_bool_then::convert_if_to_bool_then,
-            toggle_async_sugar::toggle_async_sugar,
+            toggle_async_sugar::desugar_async_into_impl_future,
+            toggle_async_sugar::sugar_impl_future_into_async,
             convert_comment_block::convert_comment_block,
             convert_from_to_tryfrom::convert_from_to_tryfrom,
             convert_integer_literal::convert_integer_literal,
diff --git a/crates/ide-assists/src/tests/generated.rs b/crates/ide-assists/src/tests/generated.rs
index 8e0d1bd667..5f187880b0 100644
--- a/crates/ide-assists/src/tests/generated.rs
+++ b/crates/ide-assists/src/tests/generated.rs
@@ -800,6 +800,23 @@ fn main() {
     )
 }
 
+#[test]
+fn doctest_desugar_async_into_impl_future() {
+    check_doc_test(
+        "desugar_async_into_impl_future",
+        r#####"
+pub async f$0n foo() -> usize {
+    0
+}
+"#####,
+        r#####"
+pub fn foo() -> impl Future<Output = usize> {
+    0
+}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_desugar_doc_comment() {
     check_doc_test(
@@ -3021,17 +3038,18 @@ use std::{collections::HashMap};
 }
 
 #[test]
-fn doctest_toggle_async_sugar() {
+fn doctest_sugar_impl_future_into_async() {
     check_doc_test(
-        "toggle_async_sugar",
+        "sugar_impl_future_into_async",
         r#####"
-pub async f$0n foo() -> usize {
-    0
+//- minicore: future
+pub f$0n foo() -> impl core::future::Future<Output = usize> {
+    async { 0 }
 }
 "#####,
         r#####"
-pub fn foo() -> impl Future<Output = usize> {
-    0
+pub async fn foo() -> usize {
+    async { 0 }
 }
 "#####,
     )

From 61f8ef5d5747858c99db8338408036a6939083d7 Mon Sep 17 00:00:00 2001
From: maxwase <max.vvase@gmail.com>
Date: Fri, 24 May 2024 01:39:46 +0300
Subject: [PATCH 3/3] Review fixes: Assist scope, trait qualify

---
 .../src/handlers/toggle_async_sugar.rs        | 164 +++++++++++++-----
 crates/ide-assists/src/tests/generated.rs     |   7 +-
 2 files changed, 126 insertions(+), 45 deletions(-)

diff --git a/crates/ide-assists/src/handlers/toggle_async_sugar.rs b/crates/ide-assists/src/handlers/toggle_async_sugar.rs
index 356e1d50ae..30e09648ea 100644
--- a/crates/ide-assists/src/handlers/toggle_async_sugar.rs
+++ b/crates/ide-assists/src/handlers/toggle_async_sugar.rs
@@ -1,3 +1,4 @@
+use hir::{ImportPathConfig, ModuleDef};
 use ide_db::{
     assists::{AssistId, AssistKind},
     famous_defs::FamousDefs,
@@ -11,13 +12,13 @@ use crate::{AssistContext, Assists};
 
 // Assist: sugar_impl_future_into_async
 //
-// Rewrites asynchronous function from `impl Future` to `async fn`.
+// Rewrites asynchronous function from `-> impl Future` into `async fn`.
 // This action does not touch the function body and therefore `async { 0 }`
 // block does not transform to just `0`.
 //
 // ```
 // # //- minicore: future
-// pub f$0n foo() -> impl core::future::Future<Output = usize> {
+// pub fn foo() -> impl core::future::F$0uture<Output = usize> {
 //     async { 0 }
 // }
 // ```
@@ -31,13 +32,10 @@ pub(crate) fn sugar_impl_future_into_async(
     acc: &mut Assists,
     ctx: &AssistContext<'_>,
 ) -> Option<()> {
-    let function: ast::Fn = ctx.find_node_at_offset()?;
-    if function.async_token().is_some() {
-        return None;
-    }
+    let ret_type: ast::RetType = ctx.find_node_at_offset()?;
+    let function = ret_type.syntax().parent().and_then(ast::Fn::cast)?;
 
-    let ret_type = function.ret_type()?;
-    if function.const_token().is_some() {
+    if function.async_token().is_some() || function.const_token().is_some() {
         return None;
     }
 
@@ -67,6 +65,7 @@ pub(crate) fn sugar_impl_future_into_async(
         function.syntax().text_range(),
         |builder| {
             match future_output {
+                // Empty tuple
                 ast::Type::TupleType(t) if t.fields().next().is_none() => {
                     let mut ret_type_range = ret_type.syntax().text_range();
 
@@ -103,18 +102,19 @@ pub(crate) fn sugar_impl_future_into_async(
 
 // Assist: desugar_async_into_impl_future
 //
-// Rewrites asynchronous function from `async fn` to `impl Future`.
+// Rewrites asynchronous function from `async fn` into `-> impl Future`.
 // This action does not touch the function body and therefore `0`
 // block does not transform to `async { 0 }`.
 //
 // ```
-// pub async f$0n foo() -> usize {
+// # //- minicore: future
+// pub as$0ync fn foo() -> usize {
 //     0
 // }
 // ```
 // ->
 // ```
-// pub fn foo() -> impl Future<Output = usize> {
+// pub fn foo() -> impl core::future::Future<Output = usize> {
 //     0
 // }
 // ```
@@ -122,8 +122,8 @@ pub(crate) fn desugar_async_into_impl_future(
     acc: &mut Assists,
     ctx: &AssistContext<'_>,
 ) -> Option<()> {
-    let function: ast::Fn = ctx.find_node_at_offset()?;
-    let async_token = function.async_token()?;
+    let async_token = ctx.find_token_syntax_at_offset(SyntaxKind::ASYNC_KW)?;
+    let function = async_token.parent().and_then(ast::Fn::cast)?;
 
     let rparen = function.param_list()?.r_paren_token()?;
     let return_type = match function.ret_type() {
@@ -133,6 +133,19 @@ pub(crate) fn desugar_async_into_impl_future(
         None => None,
     };
 
+    let scope = ctx.sema.scope(function.syntax())?;
+    let module = scope.module();
+    let future_trait = FamousDefs(&ctx.sema, scope.krate()).core_future_Future()?;
+    let trait_path = module.find_path(
+        ctx.db(),
+        ModuleDef::Trait(future_trait),
+        ImportPathConfig {
+            prefer_no_std: ctx.config.prefer_no_std,
+            prefer_prelude: ctx.config.prefer_prelude,
+        },
+    )?;
+    let trait_path = trait_path.display(ctx.db());
+
     acc.add(
         AssistId("desugar_async_into_impl_future", AssistKind::RefactorRewrite),
         "Convert async into `impl Future`",
@@ -148,9 +161,12 @@ pub(crate) fn desugar_async_into_impl_future(
             match return_type {
                 Some(ret_type) => builder.replace(
                     ret_type.syntax().text_range(),
-                    format!("impl Future<Output = {ret_type}>"),
+                    format!("impl {trait_path}<Output = {ret_type}>"),
+                ),
+                None => builder.insert(
+                    rparen.text_range().end(),
+                    format!(" -> impl {trait_path}<Output = ()>"),
                 ),
-                None => builder.insert(rparen.text_range().end(), " -> impl Future<Output = ()>"),
             }
         },
     )
@@ -186,7 +202,7 @@ mod tests {
             r#"
     //- minicore: future
     use core::future::Future;
-    f$0n foo() -> impl Future<Output = ()> {
+    fn foo() -> impl F$0uture<Output = ()> {
         todo!()
     }
     "#,
@@ -203,7 +219,7 @@ mod tests {
             r#"
     //- minicore: future
     use core::future::Future;
-    f$0n foo() -> impl Future<Output = usize> {
+    fn foo() -> impl F$0uture<Output = usize> {
         todo!()
     }
     "#,
@@ -223,7 +239,7 @@ mod tests {
             r#"
     //- minicore: future
     use core::future::Future;
-    async f$0n foo() {
+    as$0ync fn foo() {
         todo!()
     }
     "#,
@@ -239,8 +255,25 @@ mod tests {
             desugar_async_into_impl_future,
             r#"
     //- minicore: future
+    use core::future;
+    as$0ync fn foo() {
+        todo!()
+    }
+    "#,
+            r#"
+    use core::future;
+    fn foo() -> impl future::Future<Output = ()> {
+        todo!()
+    }
+    "#,
+        );
+
+        check_assist(
+            desugar_async_into_impl_future,
+            r#"
+    //- minicore: future
     use core::future::Future;
-    async f$0n foo() -> usize {
+    as$0ync fn foo() -> usize {
         todo!()
     }
     "#,
@@ -249,6 +282,23 @@ mod tests {
     fn foo() -> impl Future<Output = usize> {
         todo!()
     }
+    "#,
+        );
+
+        check_assist(
+            desugar_async_into_impl_future,
+            r#"
+    //- minicore: future
+    use core::future::Future;
+    as$0ync fn foo() -> impl Future<Output = usize> {
+        todo!()
+    }
+    "#,
+            r#"
+    use core::future::Future;
+    fn foo() -> impl Future<Output = impl Future<Output = usize>> {
+        todo!()
+    }
     "#,
         );
     }
@@ -259,7 +309,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo() -> impl core::future::Future<Output = ()> {
+    fn foo() -> impl core::future::F$0uture<Output = ()> {
         todo!()
     }
     "#,
@@ -274,7 +324,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo() -> impl core::future::Future<Output = usize> {
+    fn foo() -> impl core::future::F$0uture<Output = usize> {
         todo!()
     }
     "#,
@@ -292,12 +342,12 @@ mod tests {
             desugar_async_into_impl_future,
             r#"
     //- minicore: future
-    async f$0n foo() {
+    as$0ync fn foo() {
         todo!()
     }
     "#,
             r#"
-    fn foo() -> impl Future<Output = ()> {
+    fn foo() -> impl core::future::Future<Output = ()> {
         todo!()
     }
     "#,
@@ -307,12 +357,12 @@ mod tests {
             desugar_async_into_impl_future,
             r#"
     //- minicore: future
-    async f$0n foo() -> usize {
+    as$0ync fn foo() -> usize {
         todo!()
     }
     "#,
             r#"
-    fn foo() -> impl Future<Output = usize> {
+    fn foo() -> impl core::future::Future<Output = usize> {
         todo!()
     }
     "#,
@@ -320,7 +370,7 @@ mod tests {
     }
 
     #[test]
-    fn sugar_not_applicable() {
+    fn not_applicable() {
         check_assist_not_applicable(
             sugar_impl_future_into_async,
             r#"
@@ -328,7 +378,7 @@ mod tests {
     trait Future {
         type Output;
     }
-    f$0n foo() -> impl Future<Output = ()> {
+    fn foo() -> impl F$0uture<Output = ()> {
         todo!()
     }
     "#,
@@ -341,7 +391,26 @@ mod tests {
     trait Future {
         type Output;
     }
-    f$0n foo() -> impl Future<Output = usize> {
+    fn foo() -> impl F$0uture<Output = usize> {
+        todo!()
+    }
+    "#,
+        );
+
+        check_assist_not_applicable(
+            sugar_impl_future_into_async,
+            r#"
+    //- minicore: future
+    f$0n foo() -> impl core::future::Future<Output = usize> {
+        todo!()
+    }
+    "#,
+        );
+
+        check_assist_not_applicable(
+            desugar_async_into_impl_future,
+            r#"
+    async f$0n foo() {
         todo!()
     }
     "#,
@@ -355,7 +424,7 @@ mod tests {
             r#"
     //- minicore: future
     use core::future::Future;
-    f$0n foo() -> impl Future<Output = ()>;
+    fn foo() -> impl F$0uture<Output = ()>;
     "#,
             r#"
     use core::future::Future;
@@ -368,7 +437,7 @@ mod tests {
             r#"
     //- minicore: future
     use core::future::Future;
-    f$0n foo() -> impl Future<Output = usize>;
+    fn foo() -> impl F$0uture<Output = usize>;
     "#,
             r#"
     use core::future::Future;
@@ -383,7 +452,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo() -> impl core::future::Future<Output = ()>;
+    fn foo() -> impl core::future::F$0uture<Output = ()>;
     "#,
             r#"
     async fn foo();
@@ -394,7 +463,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo() -> impl core::future::Future<Output = usize>;
+    fn foo() -> impl core::future::F$0uture<Output = usize>;
     "#,
             r#"
     async fn foo() -> usize;
@@ -408,7 +477,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo() -> impl core::future::Future<Output = ()> + Send + Sync;
+    fn foo() -> impl core::future::F$0uture<Output = ()> + Send + Sync;
     "#,
             r#"
     async fn foo();
@@ -419,7 +488,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo() -> impl core::future::Future<Output = usize> + Debug;
+    fn foo() -> impl core::future::F$0uture<Output = usize> + Debug;
     "#,
             r#"
     async fn foo() -> usize;
@@ -430,7 +499,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo() -> impl core::future::Future<Output = (usize)> + Debug;
+    fn foo() -> impl core::future::F$0uture<Output = (usize)> + Debug;
     "#,
             r#"
     async fn foo() -> (usize);
@@ -441,10 +510,21 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo() -> impl core::future::Future<Output = (usize, usize)> + Debug;
+    fn foo() -> impl core::future::F$0uture<Output = (usize, usize)> + Debug;
     "#,
             r#"
     async fn foo() -> (usize, usize);
+    "#,
+        );
+
+        check_assist(
+            sugar_impl_future_into_async,
+            r#"
+    //- minicore: future
+    fn foo() -> impl core::future::Future<Output = impl core::future::F$0uture<Output = ()> + Send>;
+    "#,
+            r#"
+    async fn foo() -> impl core::future::Future<Output = ()> + Send;
     "#,
         );
     }
@@ -455,7 +535,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    const f$0n foo() -> impl core::future::Future<Output = ()>;
+    const fn foo() -> impl core::future::F$0uture<Output = ()>;
     "#,
         );
 
@@ -463,7 +543,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
             //- minicore: future
-            pub(crate) unsafe f$0n foo() -> impl core::future::Future<Output = usize>;
+            pub(crate) unsafe fn foo() -> impl core::future::F$0uture<Output = usize>;
         "#,
             r#"
             pub(crate) async unsafe fn foo() -> usize;
@@ -474,7 +554,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    unsafe f$0n foo() -> impl core::future::Future<Output = ()>;
+    unsafe fn foo() -> impl core::future::F$0uture<Output = ()>;
     "#,
             r#"
     async unsafe fn foo();
@@ -485,7 +565,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    unsafe extern "C" f$0n foo() -> impl core::future::Future<Output = ()>;
+    unsafe extern "C" fn foo() -> impl core::future::F$0uture<Output = ()>;
     "#,
             r#"
     async unsafe extern "C" fn foo();
@@ -496,7 +576,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo<T>() -> impl core::future::Future<Output = T>;
+    fn foo<T>() -> impl core::future::F$0uture<Output = T>;
     "#,
             r#"
     async fn foo<T>() -> T;
@@ -507,7 +587,7 @@ mod tests {
             sugar_impl_future_into_async,
             r#"
     //- minicore: future
-    f$0n foo<T>() -> impl core::future::Future<Output = T>
+    fn foo<T>() -> impl core::future::F$0uture<Output = T>
     where
         T: Sized;
     "#,
diff --git a/crates/ide-assists/src/tests/generated.rs b/crates/ide-assists/src/tests/generated.rs
index 5f187880b0..94d9e5edef 100644
--- a/crates/ide-assists/src/tests/generated.rs
+++ b/crates/ide-assists/src/tests/generated.rs
@@ -805,12 +805,13 @@ fn doctest_desugar_async_into_impl_future() {
     check_doc_test(
         "desugar_async_into_impl_future",
         r#####"
-pub async f$0n foo() -> usize {
+//- minicore: future
+pub as$0ync fn foo() -> usize {
     0
 }
 "#####,
         r#####"
-pub fn foo() -> impl Future<Output = usize> {
+pub fn foo() -> impl core::future::Future<Output = usize> {
     0
 }
 "#####,
@@ -3043,7 +3044,7 @@ fn doctest_sugar_impl_future_into_async() {
         "sugar_impl_future_into_async",
         r#####"
 //- minicore: future
-pub f$0n foo() -> impl core::future::Future<Output = usize> {
+pub fn foo() -> impl core::future::F$0uture<Output = usize> {
     async { 0 }
 }
 "#####,