late resolve, visit_fn: bail early if there's no body.

src/librustc_resolve/late.rs

@@ -456,8 +456,9 @@ impl<'a, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
     }
     fn visit_fn(&mut self, fn_kind: FnKind<'ast>, sp: Span, _: NodeId) {
         let rib_kind = match fn_kind {
-            FnKind::Fn(FnCtxt::Foreign, ..) => return visit::walk_fn(self, fn_kind, sp),
-            FnKind::Fn(FnCtxt::Free, ..) => FnItemRibKind,
+            // Bail if there's no body.
+            FnKind::Fn(.., None) => return visit::walk_fn(self, fn_kind, sp),
+            FnKind::Fn(FnCtxt::Free, ..) | FnKind::Fn(FnCtxt::Foreign, ..) => FnItemRibKind,
             FnKind::Fn(FnCtxt::Assoc(_), ..) | FnKind::Closure(..) => NormalRibKind,
         };
         let previous_value = replace(&mut self.diagnostic_metadata.current_function, Some(sp));

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

@@ -0,0 +1,6 @@
+fn main() {}
+
+trait Foo {
+    fn fn_with_type_named_same_as_local_in_param(b: b);
+    //~^ ERROR cannot find type `b` in this scope
+}

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

@@ -0,0 +1,9 @@
+error[E0412]: cannot find type `b` in this scope
+  --> $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
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0412`.