Auto merge of #129716 - compiler-errors:closure-debuginfo, r=cjgillot

Don't use `typeck_root_def_id` in codegen for finding closure's root

Generating debuginfo in codegen currently peels off all the closure-specific generics (which presumably is done because they're redundant). This doesn't currently work correctly for the bodies we synthesize for async closures's returned coroutines (#128506), leading to #129702.

Specifically, `typeck_root_def_id` for some `DefKind::SyntheticCoroutineBody` just returns itself (because it loops while `is_typeck_child` is `true`, and that returns `false` for this defkind), which means we don't end up peeling off the coroutine-specific generics, and we end up encountering an otherwise unreachable `CoroutineWitness` type leading to an ICE.

This PR fixes `is_typeck_child` to consider `DefKind::SyntheticCorotuineBody` to be a typeck child, fixing `typeck_root_def_id` and suppressing this debuginfo bug.

Fixes #129702

compiler/rustc_middle/src/ty/util.rs

@@ -571,7 +571,10 @@ pub fn is_closure_like(self, def_id: DefId) -> bool {
     /// Returns `true` if `def_id` refers to a definition that does not have its own
     /// type-checking context, i.e. closure, coroutine or inline const.
     pub fn is_typeck_child(self, def_id: DefId) -> bool {
-        matches!(self.def_kind(def_id), DefKind::Closure | DefKind::InlineConst)
+        matches!(
+            self.def_kind(def_id),
+            DefKind::Closure | DefKind::InlineConst | DefKind::SyntheticCoroutineBody
+        )
     }
 
     /// Returns `true` if `def_id` refers to a trait (i.e., `trait Foo { ... }`).

tests/ui/async-await/async-closures/debuginfo-by-move-body.rs

@@ -0,0 +1,19 @@
+//@ aux-build:block-on.rs
+//@ edition: 2021
+//@ build-pass
+//@ compile-flags: -Cdebuginfo=2
+
+#![feature(async_closure)]
+
+extern crate block_on;
+
+async fn call_once(f: impl async FnOnce()) {
+    f().await;
+}
+
+pub fn main() {
+    block_on::block_on(async {
+        let async_closure = async move || {};
+        call_once(async_closure).await;
+    });
+}