From 730ead80479d98de5cc1b555c558b5b0176fded8 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sat, 24 Sep 2022 18:53:53 +0000
Subject: [PATCH 1/2] Only generate closure def id for async fns with body

---
 compiler/rustc_resolve/src/def_collector.rs      | 10 +++++++---
 src/test/ui/async-await/in-trait/issue-102219.rs | 10 ++++++++++
 2 files changed, 17 insertions(+), 3 deletions(-)
 create mode 100644 src/test/ui/async-await/in-trait/issue-102219.rs

diff --git a/compiler/rustc_resolve/src/def_collector.rs b/compiler/rustc_resolve/src/def_collector.rs
index 3f88f44ff21a3..7e83f2a722107 100644
--- a/compiler/rustc_resolve/src/def_collector.rs
+++ b/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;
             }
         }
diff --git a/src/test/ui/async-await/in-trait/issue-102219.rs b/src/test/ui/async-await/in-trait/issue-102219.rs
new file mode 100644
index 0000000000000..9a35f6515cb1a
--- /dev/null
+++ b/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();
+}

From e99f6fee441dfa71d58b37a10366bf8c5c9d52ac Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sat, 24 Sep 2022 19:22:01 +0000
Subject: [PATCH 2/2] Only lower async fn body if it actually has a body

---
 compiler/rustc_ast_lowering/src/item.rs | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index 1251702c1ff6b..d9b18d68e537f 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -1055,9 +1055,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
         asyncness: Async,
         body: Option<&Block>,
     ) -> hir::BodyId {
-        let closure_id = match asyncness {
-            Async::Yes { closure_id, .. } => closure_id,
-            Async::No => return self.lower_fn_body_block(span, decl, body),
+        let (closure_id, body) = match (asyncness, body) {
+            (Async::Yes { closure_id, .. }, Some(body)) => (closure_id, body),
+            _ => return self.lower_fn_body_block(span, decl, body),
         };
 
         self.lower_body(|this| {
@@ -1199,16 +1199,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 parameters.push(new_parameter);
             }
 
-            let body_span = body.map_or(span, |b| b.span);
             let async_expr = this.make_async_expr(
                 CaptureBy::Value,
                 closure_id,
                 None,
-                body_span,
+                body.span,
                 hir::AsyncGeneratorKind::Fn,
                 |this| {
                     // Create a block from the user's function body:
-                    let user_body = this.lower_block_expr_opt(body_span, body);
+                    let user_body = this.lower_block_expr(body);
 
                     // Transform into `drop-temps { <user-body> }`, an expression:
                     let desugared_span =
@@ -1240,7 +1239,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
             (
                 this.arena.alloc_from_iter(parameters),
-                this.expr(body_span, async_expr, AttrVec::new()),
+                this.expr(body.span, async_expr, AttrVec::new()),
             )
         })
     }