rustdoc: Resugar async fn return type in clean, not html

This way it also happens for json output.

Fixes rust-lang#101199

Author: aDotInTheVoid

src/librustdoc/clean/mod.rs

@@ -886,7 +886,10 @@ fn clean_function<'tcx>(
         // NOTE: generics must be cleaned before args
         let generics = clean_generics(generics, cx);
         let args = clean_args_from_types_and_body_id(cx, sig.decl.inputs, body_id);
-        let decl = clean_fn_decl_with_args(cx, sig.decl, args);
+        let mut decl = clean_fn_decl_with_args(cx, sig.decl, args);
+        if sig.header.is_async() {
+            decl.output = decl.sugared_async_return_type();
+        }
         (generics, decl)
     });
     Box::new(Function { decl, generics })

src/librustdoc/html/format.rs

@@ -1310,22 +1310,19 @@ impl clean::FnDecl {
     ///   <br>Used to determine line-wrapping.
     /// * `indent`: The number of spaces to indent each successive line with, if line-wrapping is
     ///   necessary.
-    /// * `asyncness`: Whether the function is async or not.
     pub(crate) fn full_print<'a, 'tcx: 'a>(
         &'a self,
         header_len: usize,
         indent: usize,
-        asyncness: hir::IsAsync,
         cx: &'a Context<'tcx>,
     ) -> impl fmt::Display + 'a + Captures<'tcx> {
-        display_fn(move |f| self.inner_full_print(header_len, indent, asyncness, f, cx))
+        display_fn(move |f| self.inner_full_print(header_len, indent, f, cx))
     }
 
     fn inner_full_print(
         &self,
         header_len: usize,
         indent: usize,
-        asyncness: hir::IsAsync,
         f: &mut fmt::Formatter<'_>,
         cx: &Context<'_>,
     ) -> fmt::Result {
@@ -1390,15 +1387,9 @@ impl clean::FnDecl {
             args_plain.push_str(", ...");
         }
 
-        let arrow_plain;
-        let arrow = if let hir::IsAsync::Async = asyncness {
-            let output = self.sugared_async_return_type();
-            arrow_plain = format!("{:#}", output.print(cx));
-            if f.alternate() { arrow_plain.clone() } else { format!("{}", output.print(cx)) }
-        } else {
-            arrow_plain = format!("{:#}", self.output.print(cx));
-            if f.alternate() { arrow_plain.clone() } else { format!("{}", self.output.print(cx)) }
-        };
+        let arrow_plain = format!("{:#}", self.output.print(cx));
+        let arrow =
+            if f.alternate() { arrow_plain.clone() } else { format!("{}", self.output.print(cx)) };
 
         let declaration_len = header_len + args_plain.len() + arrow_plain.len();
         let output = if declaration_len > 80 {

src/librustdoc/html/render/mod.rs

@@ -821,7 +821,7 @@ fn assoc_method(
         href = href,
         name = name,
         generics = g.print(cx),
-        decl = d.full_print(header_len, indent, header.asyncness, cx),
+        decl = d.full_print(header_len, indent, cx),
         notable_traits = notable_traits_decl(d, cx),
         where_clause = print_where_clause(g, cx, indent, end_newline),
     )

src/librustdoc/html/render/print_item.rs

@@ -530,7 +530,7 @@ fn item_function(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, f: &cle
                 name = name,
                 generics = f.generics.print(cx),
                 where_clause = print_where_clause(&f.generics, cx, 0, Ending::Newline),
-                decl = f.decl.full_print(header_len, 0, header.asyncness, cx),
+                decl = f.decl.full_print(header_len, 0, cx),
                 notable_traits = notable_traits_decl(&f.decl, cx),
             );
         });

src/test/rustdoc-json/fns/async_return.rs

@@ -0,0 +1,36 @@
+// edition:2021
+// ignore-tidy-linelength
+
+// Regression test for <https://github.com/rust-lang/rust/issues/101199>
+
+use std::future::Future;
+
+// @is "$.index[*][?(@.name=='get_int')].inner.decl.output" '{"inner": "i32", "kind": "primitive"}'
+// @is "$.index[*][?(@.name=='get_int')].inner.header.async" false
+pub fn get_int() -> i32 {
+    42
+}
+
+// @is "$.index[*][?(@.name=='get_int_async')].inner.decl.output" '{"inner": "i32", "kind": "primitive"}'
+// @is "$.index[*][?(@.name=='get_int_async')].inner.header.async" true
+pub async fn get_int_async() -> i32 {
+    42
+}
+
+// @is "$.index[*][?(@.name=='get_int_future')].inner.decl.output.kind" '"impl_trait"'
+// @is "$.index[*][?(@.name=='get_int_future')].inner.decl.output.inner[0].trait_bound.trait.name" '"Future"'
+// @is "$.index[*][?(@.name=='get_int_future')].inner.decl.output.inner[0].trait_bound.trait.args.angle_bracketed.bindings[0].name" '"Output"'
+// @is "$.index[*][?(@.name=='get_int_future')].inner.decl.output.inner[0].trait_bound.trait.args.angle_bracketed.bindings[0].binding.equality.type" '{"inner": "i32", "kind": "primitive"}'
+// @is "$.index[*][?(@.name=='get_int_future')].inner.header.async" false
+pub fn get_int_future() -> impl Future<Output = i32> {
+    async { 42 }
+}
+
+// @is "$.index[*][?(@.name=='get_int_future_async')].inner.decl.output.kind" '"impl_trait"'
+// @is "$.index[*][?(@.name=='get_int_future_async')].inner.decl.output.inner[0].trait_bound.trait.name" '"Future"'
+// @is "$.index[*][?(@.name=='get_int_future_async')].inner.decl.output.inner[0].trait_bound.trait.args.angle_bracketed.bindings[0].name" '"Output"'
+// @is "$.index[*][?(@.name=='get_int_future_async')].inner.decl.output.inner[0].trait_bound.trait.args.angle_bracketed.bindings[0].binding.equality.type" '{"inner": "i32", "kind": "primitive"}'
+// @is "$.index[*][?(@.name=='get_int_future_async')].inner.header.async" true
+pub async fn get_int_future_async() -> impl Future<Output = i32> {
+    async { 42 }
+}