Only generate closure def id for async fns with body

Author: compiler-errors

compiler/rustc_resolve/src/def_collector.rs

@@ -1,6 +1,5 @@
 use crate::{ImplTraitContext, Resolver};
 use rustc_ast::visit::{self, FnKind};
-use rustc_ast::walk_list;
 use rustc_ast::*;
 use rustc_expand::expand::AstFragment;
 use rustc_hir::def_id::LocalDefId;
@@ -148,8 +147,13 @@ impl<'a, 'b> visit::Visitor<'a> for DefCollector<'a, 'b> {
                 self.with_parent(return_impl_trait_id, |this| {
                     this.visit_fn_ret_ty(&sig.decl.output)
                 });
-                let closure_def = self.create_def(closure_id, DefPathData::ClosureExpr, span);
-                self.with_parent(closure_def, |this| walk_list!(this, visit_block, body));
+                // If this async fn has no body (i.e. it's an async fn signature in a trait)
+                // then the closure_def will never be used, and we should avoid generating a
+                // def-id for it.
+                if let Some(body) = body {
+                    let closure_def = self.create_def(closure_id, DefPathData::ClosureExpr, span);
+                    self.with_parent(closure_def, |this| this.visit_block(body));
+                }
                 return;
             }
         }

src/test/ui/async-await/in-trait/issue-102219.rs

@@ -0,0 +1,10 @@
+// compile-flags:--crate-type=lib
+// edition:2021
+// check-pass
+
+#![feature(async_fn_in_trait)]
+#![allow(incomplete_features)]
+
+trait T {
+    async fn foo();
+}