Resolve async fn signature even without body (in trait)

compiler/rustc_resolve/src/late.rs

@@ -789,9 +789,8 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
         let previous_value = self.diagnostic_metadata.current_function;
         match fn_kind {
             // Bail if the function is foreign, and thus cannot validly have
-            // a body, or if there's no body for some other reason.
-            FnKind::Fn(FnCtxt::Foreign, _, sig, _, generics, _)
-            | FnKind::Fn(_, _, sig, _, generics, None) => {
+            // a body.
+            FnKind::Fn(FnCtxt::Foreign, _, sig, _, generics, _) => {
                 self.visit_fn_header(&sig.header);
                 self.visit_generics(generics);
                 self.with_lifetime_rib(

src/test/ui/async-await/in-trait/issue-102138.rs

@@ -0,0 +1,46 @@
+// check-pass
+// edition:2021
+
+#![feature(async_fn_in_trait)]
+#![allow(incomplete_features)]
+
+use std::future::Future;
+
+async fn yield_now() {}
+
+trait AsyncIterator {
+    type Item;
+    async fn next(&mut self) -> Option<Self::Item>;
+}
+
+struct YieldingRange {
+    counter: u32,
+    stop: u32,
+}
+
+impl AsyncIterator for YieldingRange {
+    type Item = u32;
+
+    async fn next(&mut self) -> Option<Self::Item> {
+        if self.counter == self.stop {
+            None
+        } else {
+            let c = self.counter;
+            self.counter += 1;
+            yield_now().await;
+            Some(c)
+        }
+    }
+}
+
+async fn async_main() {
+    let mut x = YieldingRange { counter: 0, stop: 10 };
+
+    while let Some(v) = x.next().await {
+        println!("Hi: {v}");
+    }
+}
+
+fn main() {
+    let _ = async_main();
+}

src/test/ui/async-await/issue-102138.rs

@@ -0,0 +1,46 @@
+// check-pass
+// edition:2021
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+use std::future::Future;
+
+async fn yield_now() {}
+
+trait AsyncIterator {
+    type Item;
+    async fn next(&mut self) -> Option<Self::Item>;
+}
+
+struct YieldingRange {
+    counter: u32,
+    stop: u32,
+}
+
+impl AsyncIterator for YieldingRange {
+    type Item = u32;
+
+    async fn next(&mut self) -> Option<Self::Item> {
+        if self.counter == self.stop {
+            None
+        } else {
+            let c = self.counter;
+            self.counter += 1;
+            yield_now().await;
+            Some(c)
+        }
+    }
+}
+
+async fn async_main() {
+    let mut x = YieldingRange { counter: 0, stop: 10 };
+
+    while let Some(v) = x.next().await {
+        println!("Hi: {v}");
+    }
+}
+
+fn main() {
+    let _ = async_main();
+}

src/test/ui/resolve/issue-69401-trait-fn-no-body-ty-local.rs

@@ -2,5 +2,5 @@ fn main() {}
 
 trait Foo {
     fn fn_with_type_named_same_as_local_in_param(b: b);
-    //~^ ERROR cannot find type `b` in this scope [E0412]
+    //~^ ERROR expected type, found local variable `b`
 }

src/test/ui/resolve/issue-69401-trait-fn-no-body-ty-local.stderr

@@ -1,9 +1,9 @@
-error[E0412]: cannot find type `b` in this scope
+error[E0573]: expected type, found local variable `b`
   --> $DIR/issue-69401-trait-fn-no-body-ty-local.rs:4:53
    |
 LL |     fn fn_with_type_named_same_as_local_in_param(b: b);
-   |                                                     ^ not found in this scope
+   |                                                     ^ not a type
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0412`.
+For more information about this error, try `rustc --explain E0573`.