Complete desugared and resugared async fn in trait impls

Author: Veykril

src/tools/rust-analyzer/crates/hir/src/lib.rs

@@ -2207,51 +2207,33 @@ impl Function {
         db.function_data(self.id).is_async()
     }
 
-    /// Whether this function is a `fn` that returns `impl Future`.
-    pub fn is_desugar_async(self, db: &dyn HirDatabase) -> bool {
-        if self.is_async(db) || self.is_const(db) {
-            return false;
+    pub fn returns_impl_future(self, db: &dyn HirDatabase) -> bool {
+        if self.is_async(db) {
+            return true;
         }
 
         let Some(impl_traits) = self.ret_type(db).as_impl_traits(db) else { return false };
-
         let Some(future_trait_id) =
             db.lang_item(self.ty(db).env.krate, LangItem::Future).and_then(|t| t.as_trait())
         else {
             return false;
         };
-
-        let Some(size_trait_id) =
+        let Some(sized_trait_id) =
             db.lang_item(self.ty(db).env.krate, LangItem::Sized).and_then(|t| t.as_trait())
         else {
             return false;
         };
 
-        let Some(sync_trait_id) =
-            db.lang_item(self.ty(db).env.krate, LangItem::Sync).and_then(|t| t.as_trait())
-        else {
-            return false;
-        };
-
-        // TODO: There's no `LangItem::Send`. How do we get the id of `Send` trait?
-        // let Some(send_trait_id) = db.lang_item(self.ty(db).env.krate, LangItem::Send).and_then(|t| t.as_trait()) else {
-        //     eprint!("no future_trait_id\n");
-        //     return false
-        // };
-
-        let allowed_to_leaked_types = vec![size_trait_id, sync_trait_id];
-
         let mut has_impl_future = false;
-        let mut has_types_not_allow_to_leaked = false;
-        for impl_trait in impl_traits {
-            if impl_trait.id == future_trait_id {
-                has_impl_future = true;
-            } else if !allowed_to_leaked_types.contains(&impl_trait.id) {
-                has_types_not_allow_to_leaked = true;
-            }
-        }
-
-        has_impl_future && !has_types_not_allow_to_leaked
+        impl_traits
+            .filter(|t| {
+                let fut = t.id == future_trait_id;
+                has_impl_future |= fut;
+                !fut && t.id != sized_trait_id
+            })
+            // all traits but the future trait must be auto traits
+            .all(|t| t.is_auto(db))
+            && has_impl_future
     }
 
     /// Does this function have `#[test]` attribute?