rustdoc: correctly render ret ty of cross-crate async fns

Author: fmease

src/librustdoc/clean/inline.rs

@@ -253,7 +253,10 @@ fn build_external_function<'tcx>(cx: &mut DocContext<'tcx>, did: DefId) -> Box<c
         let mut generics = clean_ty_generics(cx, cx.tcx.generics_of(did), predicates);
         // FIXME: This does not place parameters in source order (late-bound ones come last)
         generics.params.extend(late_bound_regions);
-        let decl = clean_fn_decl_from_did_and_sig(cx, Some(did), sig);
+        let mut decl = clean_fn_decl_from_did_and_sig(cx, Some(did), sig);
+        if cx.tcx.asyncness(did).is_async() {
+            decl.output = decl.sugared_async_return_type();
+        }
         (generics, decl)
     });
     Box::new(clean::Function { decl, generics })

src/librustdoc/clean/mod.rs

@@ -1370,6 +1370,9 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
             generics.params.extend(late_bound_regions);
 
             let mut decl = clean_fn_decl_from_did_and_sig(cx, Some(assoc_item.def_id), sig);
+            if tcx.asyncness(assoc_item.def_id).is_async() {
+                decl.output = decl.sugared_async_return_type();
+            }
 
             if assoc_item.fn_has_self_parameter {
                 let self_ty = match assoc_item.container {

tests/rustdoc/inline_cross/async-fn.rs

@@ -0,0 +1,19 @@
+// Regression test for issue #115760.
+// Check that we render the correct return type of free and
+// associated async functions reexported from external crates.
+
+// aux-crate:async_fn=async-fn.rs
+// edition: 2021
+#![crate_name = "user"]
+
+// @has user/fn.load.html
+// @has - '//pre[@class="rust item-decl"]' "pub async fn load() -> i32"
+pub use async_fn::load;
+
+// @has user/trait.Load.html
+// @has - '//*[@id="tymethod.run"]' 'async fn run(&self) -> i32'
+pub use async_fn::Load;
+
+// @has user/struct.Loader.html
+// @has - '//*[@id="method.run"]' 'async fn run(&self) -> i32'
+pub use async_fn::Loader;

tests/rustdoc/inline_cross/auxiliary/async-fn.rs

@@ -0,0 +1,18 @@
+#![feature(async_fn_in_trait)]
+// edition: 2021
+
+pub async fn load() -> i32 {
+    0
+}
+
+pub trait Load {
+    async fn run(&self) -> i32;
+}
+
+pub struct Loader;
+
+impl Load for Loader {
+    async fn run(&self) -> i32 {
+        1
+    }
+}

tests/rustdoc/inline_cross/auxiliary/impl_trait_aux.rs

@@ -33,9 +33,3 @@ pub struct Foo;
 impl Foo {
     pub fn method<'a>(_x: impl Clone + Into<Vec<u8>> + 'a) {}
 }
-
-pub struct Bar;
-
-impl Bar {
-    pub async fn async_foo(&self) {}
-}

tests/rustdoc/inline_cross/impl_trait.rs

@@ -33,15 +33,7 @@ pub use impl_trait_aux::func4;
 // @!has - '//pre[@class="rust item-decl"]' 'where'
 pub use impl_trait_aux::func5;
 
-// @has impl_trait/fn.async_fn.html
-// @has - '//pre[@class="rust item-decl"]' "pub async fn async_fn()"
-pub use impl_trait_aux::async_fn;
-
 // @has impl_trait/struct.Foo.html
 // @has - '//*[@id="method.method"]//h4[@class="code-header"]' "pub fn method<'a>(_x: impl Clone + Into<Vec<u8, Global>> + 'a)"
 // @!has - '//*[@id="method.method"]//h4[@class="code-header"]' 'where'
 pub use impl_trait_aux::Foo;
-
-// @has impl_trait/struct.Bar.html
-// @has - '//*[@id="method.async_foo"]' "pub async fn async_foo("
-pub use impl_trait_aux::Bar;