From d83f3ca8ca2d20eadf92a135a1a4b65ca91a24f6 Mon Sep 17 00:00:00 2001
From: Scott McMurray <scottmcm@users.noreply.github.com>
Date: Thu, 23 May 2024 23:17:58 -0700
Subject: Validate the special layout restriction on DynMetadata

---
 compiler/rustc_const_eval/src/transform/validate.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'compiler/rustc_const_eval/src')

diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 3a2b2c5f300..66cc65de647 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -685,6 +685,15 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                         check_equal(self, location, *f_ty);
                     }
                     ty::Adt(adt_def, args) => {
+                        // see <https://github.com/rust-lang/rust/blob/7601adcc764d42c9f2984082b49948af652df986/compiler/rustc_middle/src/ty/layout.rs#L861-L864>
+                        if Some(adt_def.did()) == self.tcx.lang_items().dyn_metadata() {
+                            self.fail(
+                                location,
+                                format!("You can't project to field {f:?} of `DynMetadata` because \
+                                         layout is weird and thinks it doesn't have fields."),
+                            );
+                        }
+
                         let var = parent_ty.variant_index.unwrap_or(FIRST_VARIANT);
                         let Some(field) = adt_def.variant(var).fields.get(f) else {
                             fail_out_of_bounds(self, location);
-- 
cgit 1.4.1-3-g733a5