[clang] [clang] Check `T` and `U` operands of __reference_constructs_from_temporary are complete types (PR #206703)

[Yihan Wang via cfe-commits]

https://github.com/yronglin updated https://github.com/llvm/llvm-project/pull/206703

>From c9e3e6194e58b65a611bad3e356119495ffb5e12 Mon Sep 17 00:00:00 2001
From: yronglin <yronglin777 at gmail.com>
Date: Tue, 30 Jun 2026 03:02:51 -0700
Subject: [PATCH 1/3] [clang] Check precondition of
 __reference_constructs_from_temporary

Signed-off-by: yronglin <yronglin777 at gmail.com>
---
 clang/lib/Sema/SemaTypeTraits.cpp             | 5 ++---
 clang/test/SemaCXX/type-traits-incomplete.cpp | 6 ++++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index 4de73601e273d..e3ae6095c846c 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -1292,8 +1292,6 @@ static bool EvaluateBooleanTypeTrait(Sema &S, TypeTrait Kind,
         Kind == clang::BTT_ReferenceBindsToTemporary ||
         Kind == clang::BTT_ReferenceConstructsFromTemporary ||
         Kind == clang::BTT_ReferenceConvertsFromTemporary;
-    if (UseRawObjectType && !Args[0]->getType()->isReferenceType())
-      return false;
 
     // Precondition: T and all types in the parameter pack Args shall be
     // complete types, (possibly cv-qualified) void, or arrays of
@@ -1310,7 +1308,8 @@ static bool EvaluateBooleanTypeTrait(Sema &S, TypeTrait Kind,
 
     // Make sure the first argument is not incomplete nor a function type.
     QualType T = Args[0]->getType();
-    if (T->isIncompleteType() || T->isFunctionType())
+    if (T->isIncompleteType() || T->isFunctionType() ||
+        (UseRawObjectType && !T->isReferenceType()))
       return false;
 
     // Make sure the first argument is not an abstract type.
diff --git a/clang/test/SemaCXX/type-traits-incomplete.cpp b/clang/test/SemaCXX/type-traits-incomplete.cpp
index 3e341d6482440..2f56b5fa81820 100644
--- a/clang/test/SemaCXX/type-traits-incomplete.cpp
+++ b/clang/test/SemaCXX/type-traits-incomplete.cpp
@@ -12,3 +12,9 @@ void f() {
   __is_trivially_relocatable(S); // expected-error{{incomplete type 'S' used in type trait expression}}
   __is_trivially_relocatable(S[]); // expected-error{{incomplete type 'S' used in type trait expression}}
 }
+
+struct NoConv;
+struct Bad;
+
+constexpr bool a = __reference_constructs_from_temporary(S, NoConv&&); // expected-error{{incomplete type 'Bad' used in type trait expression}}
+

>From b4735ced8f51e7027553400b53bad54eff4b6dad Mon Sep 17 00:00:00 2001
From: Yihan Wang <yronglin777 at gmail.com>
Date: Tue, 30 Jun 2026 19:55:44 +0800
Subject: [PATCH 2/3] Fix test

---
 clang/test/SemaCXX/type-traits-incomplete.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/test/SemaCXX/type-traits-incomplete.cpp b/clang/test/SemaCXX/type-traits-incomplete.cpp
index 2f56b5fa81820..b5b4df9a8f743 100644
--- a/clang/test/SemaCXX/type-traits-incomplete.cpp
+++ b/clang/test/SemaCXX/type-traits-incomplete.cpp
@@ -16,5 +16,5 @@ void f() {
 struct NoConv;
 struct Bad;
 
-constexpr bool a = __reference_constructs_from_temporary(S, NoConv&&); // expected-error{{incomplete type 'Bad' used in type trait expression}}
+constexpr bool a = __reference_constructs_from_temporary(Bad, NoConv&&); // expected-error{{incomplete type 'Bad' used in type trait expression}}
 

>From 47541af93c33f12ee5cc9ebba9cd5abd7ed0c326 Mon Sep 17 00:00:00 2001
From: Yihan Wang <yronglin777 at gmail.com>
Date: Tue, 30 Jun 2026 20:07:30 +0800
Subject: [PATCH 3/3] Fix Test

---
 clang/test/SemaCXX/type-traits-incomplete.cpp | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/clang/test/SemaCXX/type-traits-incomplete.cpp b/clang/test/SemaCXX/type-traits-incomplete.cpp
index b5b4df9a8f743..44941f7ee41a3 100644
--- a/clang/test/SemaCXX/type-traits-incomplete.cpp
+++ b/clang/test/SemaCXX/type-traits-incomplete.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s 
 
-struct S; // expected-note 6 {{forward declaration of 'S'}}
+struct S; // expected-note 7 {{forward declaration of 'S'}}
 
 void f() {
   __is_pod(S); // expected-error{{incomplete type 'S' used in type trait expression}}
@@ -14,7 +14,6 @@ void f() {
 }
 
 struct NoConv;
-struct Bad;
 
-constexpr bool a = __reference_constructs_from_temporary(Bad, NoConv&&); // expected-error{{incomplete type 'Bad' used in type trait expression}}
+constexpr bool a = __reference_constructs_from_temporary(S, NoConv&&); // expected-error{{incomplete type 'S' used in type trait expression}}