[clang] fc1565f - [clang] Check `T` and `U` operands of __reference_constructs_from_temporary are complete types (#206703)

[via cfe-commits]

Author: Yihan Wang
Date: 2026-07-02T23:37:59+08:00
New Revision: fc1565f89eaff7b4594186793cbb04862660ecff

URL: https://github.com/llvm/llvm-project/commit/fc1565f89eaff7b4594186793cbb04862660ecff
DIFF: https://github.com/llvm/llvm-project/commit/fc1565f89eaff7b4594186793cbb04862660ecff.diff

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

This PR fix a bug introduce by
https://github.com/llvm/llvm-project/pull/206527.

[type.traits] Precondition : "T and U shall be complete types, cv void,
or arrays of unknown bound first.

The check for which
[#206527](https://github.com/llvm/llvm-project/pull/206527.) disables if
the first argument isn't a reference type.

---------

Signed-off-by: yronglin <yronglin777 at gmail.com>

Added: 
    

Modified: 
    clang/lib/Sema/SemaTypeTraits.cpp
    clang/test/SemaCXX/type-traits-incomplete.cpp

Removed: 
    


################################################################################
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..2e09d60eecd81 100644
--- a/clang/test/SemaCXX/type-traits-incomplete.cpp
+++ b/clang/test/SemaCXX/type-traits-incomplete.cpp
@@ -1,6 +1,9 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s 
 
-struct S; // expected-note 6 {{forward declaration of 'S'}}
+struct S; // expected-note 8 {{forward declaration of 'S'}}
+
+struct NoConv {};
+struct Bad { template<class T> Bad(T v) noexcept(noexcept(member_ = v)) {} int member_; };
 
 void f() {
   __is_pod(S); // expected-error{{incomplete type 'S' used in type trait expression}}
@@ -11,4 +14,7 @@ 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}}
+
+  static_assert(!__reference_constructs_from_temporary(S, NoConv&&)); // expected-error{{incomplete type 'S' used in type trait expression}}
+  static_assert(!__reference_constructs_from_temporary(Bad, S)); // expected-error{{incomplete type 'S' used in type trait expression}}
 }