Only assert for child/parent projection compatibility AFTER checking that theyre coming from the same place

Author: compiler-errors

compiler/rustc_mir_transform/src/coroutine/by_move_body.rs

@@ -156,9 +156,6 @@ impl<'tcx> MirPass<'tcx> for ByMoveBody {
                     bug!("expected capture to be an upvar");
                 };
 
-                assert!(
-                    child_capture.place.projections.len() >= parent_capture.place.projections.len()
-                );
                 // A parent matches a child they share the same prefix of projections.
                 // The child may have more, if it is capturing sub-fields out of
                 // something that is captured by-move in the parent closure.
@@ -180,6 +177,14 @@ impl<'tcx> MirPass<'tcx> for ByMoveBody {
                     continue;
                 }
 
+                // This analysis only makes sense if the parent capture is a
+                // prefix of the child capture.
+                assert!(
+                    child_capture.place.projections.len() >= parent_capture.place.projections.len(),
+                    "parent capture ({parent_capture:#?}) expected to be prefix of \
+                child capture ({child_capture:#?})"
+                );
+
                 // Store this set of additional projections (fields and derefs).
                 // We need to re-apply them later.
                 let child_precise_captures =

tests/ui/async-await/async-closures/different-projection-lengths-for-different-upvars.rs

@@ -0,0 +1,16 @@
+//@ check-pass
+//@ edition: 2021
+// issue: rust-lang/rust#123697
+
+#![feature(async_closure)]
+
+struct S { t: i32 }
+
+fn test(s: &S, t: &i32) {
+    async || {
+        println!("{}", s.t);
+        println!("{}", t);
+    };
+}
+
+fn main() {}