From 0031cf7c7e5bd255a504df19f44cc0eaf240fd57 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Wed, 27 Sep 2023 11:35:09 +0000
Subject: [PATCH] Add a mir validation check to prevent OpaqueCast after
 analysis passes finish

---
 compiler/rustc_const_eval/src/transform/validate.rs | 8 ++++++++
 compiler/rustc_middle/src/mir/syntax.rs             | 1 +
 2 files changed, 9 insertions(+)

diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 0d8733070a446..18b22882e7d08 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -633,6 +633,14 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
         location: Location,
     ) {
         match elem {
+            ProjectionElem::OpaqueCast(ty)
+                if self.mir_phase >= MirPhase::Runtime(RuntimePhase::Initial) =>
+            {
+                self.fail(
+                    location,
+                    format!("explicit opaque type cast to `{ty}` after `RevealAll`"),
+                )
+            }
             ProjectionElem::Index(index) => {
                 let index_ty = self.body.local_decls[index].ty;
                 if index_ty != self.tcx.types.usize {
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 201926fee3e02..55f895f73b48b 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -139,6 +139,7 @@ pub enum RuntimePhase {
     /// * [`TerminatorKind::Yield`]
     /// * [`TerminatorKind::GeneratorDrop`]
     /// * [`Rvalue::Aggregate`] for any `AggregateKind` except `Array`
+    /// * [`PlaceElem::OpaqueCast`]
     ///
     /// And the following variants are allowed:
     /// * [`StatementKind::Retag`]