[clang] [ObjC] Fix Assertion failure when merging declarations with different lifetime qualifiers (PR #203272)

[Hendrik Hübner via cfe-commits]

https://github.com/HendrikHuebner updated https://github.com/llvm/llvm-project/pull/203272

>From 9b78ed33016420997619a0cda5d318ef01aa15b5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hendrik=20H=C3=BCbner?= <hhuebner at MacBookPro.localdomain>
Date: Thu, 11 Jun 2026 15:55:55 +0200
Subject: [PATCH 1/3] [ObjC] Fix Assertion failure when merging declarations
 with different lifetime qualifiers

Fixes #150403
---
 clang/lib/AST/ASTContext.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index abf0cd5e18c2b..e936572458444 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -12356,7 +12356,8 @@ QualType ASTContext::mergeObjCGCQualifiers(QualType LHS, QualType RHS) {
   if (LQuals != RQuals) {
     // If any of these qualifiers are different, we have a type mismatch.
     if (LQuals.getCVRQualifiers() != RQuals.getCVRQualifiers() ||
-        LQuals.getAddressSpace() != RQuals.getAddressSpace())
+        LQuals.getAddressSpace() != RQuals.getAddressSpace() ||
+        LQuals.getObjCLifetime() != RQuals.getObjCLifetime())
       return {};
 
     // Exactly one GC qualifier difference is allowed: __strong is

>From 7b37b95ce45e0b3d8243e4a2624d42db3d35c795 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hendrik=20H=C3=BCbner?= <hhuebner at MacBookPro.localdomain>
Date: Thu, 11 Jun 2026 16:06:06 +0200
Subject: [PATCH 2/3] add test

---
 clang/test/SemaObjC/arc-repeated-weak.mm | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/clang/test/SemaObjC/arc-repeated-weak.mm b/clang/test/SemaObjC/arc-repeated-weak.mm
index aaf8256d314ee..45b9816b42057 100644
--- a/clang/test/SemaObjC/arc-repeated-weak.mm
+++ b/clang/test/SemaObjC/arc-repeated-weak.mm
@@ -340,6 +340,9 @@ - (void)distinctFromOther:(Test *)other {
 }
 @end
 
+extern id foo; // expected-note {{previous declaration is here}}
+extern __weak id foo; // expected-error {{redeclaration of 'foo' with a different type}}
+
 @interface Base1
 @end
 @interface Sub1 : Base1

>From e309724911cf3074b6973304850acc056137c33d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hendrik=20H=C3=BCbner?= <hhuebner at MacBookPro.lan>
Date: Fri, 12 Jun 2026 10:54:40 +0200
Subject: [PATCH 3/3] Fix test and logic

---
 clang/lib/AST/ASTContext.cpp             | 13 +++++--------
 clang/test/SemaObjC/arc-repeated-weak.mm |  6 +++---
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index e936572458444..a4d7ded4bf50e 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -12339,7 +12339,7 @@ QualType ASTContext::mergeObjCGCQualifiers(QualType LHS, QualType RHS) {
       // id foo(); ... __strong id foo(); or: __strong id foo(); ... id foo();
       // In either case, use OldReturnType to build the new function type.
       const auto *F = LHS->castAs<FunctionType>();
-      if (const auto *FPT = cast<FunctionProtoType>(F)) {
+      if (const auto *FPT = cast_or_null<FunctionProtoType>(F)) {
         FunctionProtoType::ExtProtoInfo EPI = FPT->getExtProtoInfo();
         EPI.ExtInfo = getFunctionExtInfo(LHS);
         QualType ResultType =
@@ -12354,12 +12354,6 @@ QualType ASTContext::mergeObjCGCQualifiers(QualType LHS, QualType RHS) {
   Qualifiers LQuals = LHSCan.getLocalQualifiers();
   Qualifiers RQuals = RHSCan.getLocalQualifiers();
   if (LQuals != RQuals) {
-    // If any of these qualifiers are different, we have a type mismatch.
-    if (LQuals.getCVRQualifiers() != RQuals.getCVRQualifiers() ||
-        LQuals.getAddressSpace() != RQuals.getAddressSpace() ||
-        LQuals.getObjCLifetime() != RQuals.getObjCLifetime())
-      return {};
-
     // Exactly one GC qualifier difference is allowed: __strong is
     // okay if the other type has no GC qualifier but is an Objective
     // C object pointer (i.e. implicitly strong by default).  We fix
@@ -12367,7 +12361,10 @@ QualType ASTContext::mergeObjCGCQualifiers(QualType LHS, QualType RHS) {
     // qualified __strong.
     Qualifiers::GC GC_L = LQuals.getObjCGCAttr();
     Qualifiers::GC GC_R = RQuals.getObjCGCAttr();
-    assert((GC_L != GC_R) && "unequal qualifier sets had only equal elements");
+    if (GC_L == GC_R) {
+      // Some non-GC qualifiers differ, so merging fails.
+      return {};
+    }
 
     if (GC_L == Qualifiers::Weak || GC_R == Qualifiers::Weak)
       return {};
diff --git a/clang/test/SemaObjC/arc-repeated-weak.mm b/clang/test/SemaObjC/arc-repeated-weak.mm
index 45b9816b42057..ecffd77faa203 100644
--- a/clang/test/SemaObjC/arc-repeated-weak.mm
+++ b/clang/test/SemaObjC/arc-repeated-weak.mm
@@ -340,9 +340,6 @@ - (void)distinctFromOther:(Test *)other {
 }
 @end
 
-extern id foo; // expected-note {{previous declaration is here}}
-extern __weak id foo; // expected-error {{redeclaration of 'foo' with a different type}}
-
 @interface Base1
 @end
 @interface Sub1 : Base1
@@ -512,3 +509,6 @@ -(void)m {
   (void)self.nd[@""]; // no warning
 }
 @end
+
+extern id mergeQualsVar; // expected-note {{previous declaration is here}}
+extern __weak id mergeQualsVar; // expected-error {{redeclaration of 'mergeQualsVar' with a different type}}