[llvm-branch-commits] [clang] release/19.x: [clang] Remove `__is_layout_compatible` from revertible type traits list (#100572) (PR #100590)

[Tobias Hieta via llvm-branch-commits]

https://github.com/tru updated https://github.com/llvm/llvm-project/pull/100590

>From d767c52c26d7f9a143b23934917645efe0763364 Mon Sep 17 00:00:00 2001
From: Vlad Serebrennikov <serebrennikov.vladislav at gmail.com>
Date: Thu, 25 Jul 2024 20:15:14 +0400
Subject: [PATCH] [clang] Remove `__is_layout_compatible` from revertible type
 traits list (#100572)

`__is_layout_compatible` was added in Clang 19 (#81506), and at that
time it wasn't entirely clear whether it should be a revertible type
trait or not. We decided to follow the example of other type traits.
Since then #95969 happened, and now we know that we don't want new
revertible type traits.

This patch removes `__is_layout_compatible` from revertible type traits
list, and leaves a comment what revertible type traits are, and that new
type traits should not be added there.

The intention is to also cherry-pick this to 19 branch.

(cherry picked from commit 3295d377f37a60597321f502d164b5d6b1948e28)
---
 clang/lib/Parse/ParseExpr.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index 0a017ae79de753..e82b5652728317 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -763,6 +763,9 @@ class CastExpressionIdValidator final : public CorrectionCandidateCallback {
 bool Parser::isRevertibleTypeTrait(const IdentifierInfo *II,
                                    tok::TokenKind *Kind) {
   if (RevertibleTypeTraits.empty()) {
+// Revertible type trait is a feature for backwards compatibility with older
+// standard libraries that declare their own structs with the same name as
+// the builtins listed below. New builtins should NOT be added to this list.
 #define RTT_JOIN(X, Y) X##Y
 #define REVERTIBLE_TYPE_TRAIT(Name)                                            \
   RevertibleTypeTraits[PP.getIdentifierInfo(#Name)] = RTT_JOIN(tok::kw_, Name)
@@ -790,7 +793,6 @@ bool Parser::isRevertibleTypeTrait(const IdentifierInfo *II,
     REVERTIBLE_TYPE_TRAIT(__is_fundamental);
     REVERTIBLE_TYPE_TRAIT(__is_integral);
     REVERTIBLE_TYPE_TRAIT(__is_interface_class);
-    REVERTIBLE_TYPE_TRAIT(__is_layout_compatible);
     REVERTIBLE_TYPE_TRAIT(__is_literal);
     REVERTIBLE_TYPE_TRAIT(__is_lvalue_expr);
     REVERTIBLE_TYPE_TRAIT(__is_lvalue_reference);