Rollup merge of #60527 - davidtwco:issue-60518, r=cramertj

Fix async fn lowering ICE with APIT.

Fixes #60518.

This PR fixes an ICE where simple bindings (which aren't replaced with replacement arguments during async fn lowering) were not being visited in the def collector and thus caused an ICE during HIR lowering for types that use their `DefId` at that point - such as `impl Trait`.

r? @cramertj

2 files changed, 15 insertions, 1 deletions

diff --git a/src/librustc/hir/map/def_collector.rs b/src/librustc/hir/map/def_collector.rs
index 78de8539859..7f1352095d9 100644
--- a/src/librustc/hir/map/def_collector.rs
+++ b/src/librustc/hir/map/def_collector.rs
@@ -92,10 +92,12 @@ impl<'a> DefCollector<'a> {
             visit::walk_generics(this, generics);
 
             // Walk the generated arguments for the `async fn`.
-            for a in arguments {
+            for (i, a) in arguments.iter().enumerate() {
                 use visit::Visitor;
                 if let Some(arg) = &a.arg {
                     this.visit_ty(&arg.ty);
+                } else {
+                    this.visit_ty(&decl.inputs[i].ty);
                 }
             }
 
diff --git a/src/test/ui/async-await/issue-60518.rs b/src/test/ui/async-await/issue-60518.rs
new file mode 100644
index 00000000000..f603c5bd3f9
--- /dev/null
+++ b/src/test/ui/async-await/issue-60518.rs
@@ -0,0 +1,12 @@
+// compile-pass
+// edition:2018
+
+#![feature(async_await)]
+
+// This is a regression test to ensure that simple bindings (where replacement arguments aren't
+// created during async fn lowering) that have their DefId used during HIR lowering (such as impl
+// trait) are visited during def collection and thus have a DefId.
+
+async fn foo(ws: impl Iterator<Item = ()>) {}
+
+fn main() {}