[clang] [Clang] Fix isWeakImported() to traverse redeclaration chain for avai… (PR #181482)
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Mon Apr 13 05:10:15 PDT 2026
https://github.com/kevinlzh1108 updated https://github.com/llvm/llvm-project/pull/181482
>From 7f9f455552f801a11033371e8d0acbca07e52273 Mon Sep 17 00:00:00 2001
From: kevinlzh1108 <kevinlzh1108 at gmail.com>
Date: Sat, 14 Feb 2026 22:41:32 +0800
Subject: [PATCH 1/2] [Clang] Fix isWeakImported() to traverse redeclaration
chain for availability attributes
Decl::isWeakImported() only checked attributes on getMostRecentDecl(),
which missed availability attributes on earlier declarations in the
redeclaration chain. This caused incorrect strong linking when a forward
declaration (@class) without availability attributes became the most
recent declaration, shadowing the original @interface declaration that
carried the availability(ios,introduced=14.0) attribute.
This is particularly problematic with Clang Modules and Precompiled
Headers (PCH), where module deserialization order can cause a forward
declaration from one module (e.g., UIKit's @class UTType) to become
the most recent declaration, even though the original @interface
declaration (in UniformTypeIdentifiers) has the availability attribute.
The fix changes isWeakImported() to iterate over all redeclarations
using redecls(), consistent with how Decl::isReferenced() already
traverses the redeclaration chain in the same file.
Fixes a bug where apps targeting iOS < 14.0 would strongly link
UniformTypeIdentifiers symbols instead of weak-linking them, causing
crashes on older iOS versions.
---
clang/lib/AST/DeclBase.cpp | 18 ++++---
.../attr-availability-redecl-weak.m | 47 +++++++++++++++++++
2 files changed, 58 insertions(+), 7 deletions(-)
create mode 100644 clang/test/CodeGenObjC/attr-availability-redecl-weak.m
diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index 0a1e442656c35..0c122f808dea4 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -872,14 +872,18 @@ bool Decl::isWeakImported() const {
if (!canBeWeakImported(IsDefinition))
return false;
- for (const auto *A : getMostRecentDecl()->attrs()) {
- if (isa<WeakImportAttr>(A))
- return true;
-
- if (const auto *Availability = dyn_cast<AvailabilityAttr>(A)) {
- if (CheckAvailability(getASTContext(), Availability, nullptr,
- VersionTuple()) == AR_NotYetIntroduced)
+ // Traverse the entire redeclaration chain, since availability attributes
+ // may not be present on the most recent declaration (e.g., a @class forward
+ // declaration may lack the availability attribute from the @interface).
+ for (const auto *D : redecls()) {
+ for (const auto *A : D->attrs()) {
+ if (isa<WeakImportAttr>(A))
return true;
+
+ if (const auto *Availability = dyn_cast<AvailabilityAttr>(A))
+ if (CheckAvailability(getASTContext(), Availability, nullptr,
+ VersionTuple()) == AR_NotYetIntroduced)
+ return true;
}
}
diff --git a/clang/test/CodeGenObjC/attr-availability-redecl-weak.m b/clang/test/CodeGenObjC/attr-availability-redecl-weak.m
new file mode 100644
index 0000000000000..e1000e66a6042
--- /dev/null
+++ b/clang/test/CodeGenObjC/attr-availability-redecl-weak.m
@@ -0,0 +1,47 @@
+// RUN: %clang_cc1 -triple arm64-apple-ios12.0 -emit-llvm -o - %s | FileCheck %s
+
+// Test that isWeakImported() correctly traverses the redeclaration chain
+// to find availability attributes, even when a forward declaration (@class)
+// without availability attributes becomes the most recent declaration.
+
+// Case 1: @interface (with availability) first, then @class (without availability).
+// The @class becomes getMostRecentDecl(). Without the fix, isWeakImported()
+// would only check the @class's attributes and miss the availability attribute,
+// resulting in strong linkage instead of extern_weak.
+
+__attribute__((availability(ios,introduced=14.0)))
+ at interface WeakRedecl1
+ at end
+
+ at class WeakRedecl1;
+
+ at implementation WeakRedecl1 (TestCategory1)
+ at end
+
+// CHECK: @"OBJC_CLASS_$_WeakRedecl1" = extern_weak global
+
+// Case 2: @class first, then @interface (with availability).
+// This order already worked before the fix because @interface becomes
+// getMostRecentDecl() and carries the availability attribute.
+// We test it here to ensure the fix doesn't regress this case.
+
+ at class WeakRedecl2;
+
+__attribute__((availability(ios,introduced=14.0)))
+ at interface WeakRedecl2
+ at end
+
+ at implementation WeakRedecl2 (TestCategory2)
+ at end
+
+// CHECK: @"OBJC_CLASS_$_WeakRedecl2" = extern_weak global
+
+// Case 3: Single declaration with availability (baseline, no redeclaration).
+__attribute__((availability(ios,introduced=14.0)))
+ at interface WeakSingle
+ at end
+
+ at implementation WeakSingle (TestCategory3)
+ at end
+
+// CHECK: @"OBJC_CLASS_$_WeakSingle" = extern_weak global
>From 374420f77132fa1809c34eeb768827115c1ba1c7 Mon Sep 17 00:00:00 2001
From: kevinlzh1108 <kevinlzh1108 at gmail.com>
Date: Mon, 13 Apr 2026 20:08:31 +0800
Subject: [PATCH 2/2] [Clang] Replace single-file test with Clang Modules test
for isWeakImported() fix
The previous single-file test (attr-availability-redecl-weak.m) was not a
valid reduction: within a single translation unit, Sema's mergeDeclAttributes()
automatically merges all availability attributes from @interface to @class,
so the old getMostRecentDecl()->attrs() code also found the ios availability
attribute. The test passed with or without the fix.
Replace it with a Clang Modules test that reproduces the actual bug:
- InterfaceMod: @interface with availability(macos,introduced=11.0) and
availability(ios,introduced=14.0) (macos listed first)
- ForwardMod: bare @class (no availability attributes)
When InterfaceMod is imported first and ForwardMod second, the @class becomes
getMostRecentDecl(). Cross-PCM mergeInheritableAttributes (ASTReaderDecl.cpp)
uses getAttr<AvailabilityAttr>() which only copies the first AvailabilityAttr
(macos), losing the ios attr. The old isWeakImported() only checked
getMostRecentDecl()->attrs(), found only macos (wrong platform), and
incorrectly returned false (strong linkage).
Both import orders are tested to ensure no regression.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply at anthropic.com>
---
.../attr-availability-redecl-weak.m | 47 -------------------
.../Inputs/availability-redecl-weak/forward.h | 1 +
.../availability-redecl-weak/interface.h | 8 ++++
.../availability-redecl-weak/module.modulemap | 2 +
clang/test/Modules/availability-redecl-weak.m | 39 +++++++++++++++
5 files changed, 50 insertions(+), 47 deletions(-)
delete mode 100644 clang/test/CodeGenObjC/attr-availability-redecl-weak.m
create mode 100644 clang/test/Modules/Inputs/availability-redecl-weak/forward.h
create mode 100644 clang/test/Modules/Inputs/availability-redecl-weak/interface.h
create mode 100644 clang/test/Modules/Inputs/availability-redecl-weak/module.modulemap
create mode 100644 clang/test/Modules/availability-redecl-weak.m
diff --git a/clang/test/CodeGenObjC/attr-availability-redecl-weak.m b/clang/test/CodeGenObjC/attr-availability-redecl-weak.m
deleted file mode 100644
index e1000e66a6042..0000000000000
--- a/clang/test/CodeGenObjC/attr-availability-redecl-weak.m
+++ /dev/null
@@ -1,47 +0,0 @@
-// RUN: %clang_cc1 -triple arm64-apple-ios12.0 -emit-llvm -o - %s | FileCheck %s
-
-// Test that isWeakImported() correctly traverses the redeclaration chain
-// to find availability attributes, even when a forward declaration (@class)
-// without availability attributes becomes the most recent declaration.
-
-// Case 1: @interface (with availability) first, then @class (without availability).
-// The @class becomes getMostRecentDecl(). Without the fix, isWeakImported()
-// would only check the @class's attributes and miss the availability attribute,
-// resulting in strong linkage instead of extern_weak.
-
-__attribute__((availability(ios,introduced=14.0)))
- at interface WeakRedecl1
- at end
-
- at class WeakRedecl1;
-
- at implementation WeakRedecl1 (TestCategory1)
- at end
-
-// CHECK: @"OBJC_CLASS_$_WeakRedecl1" = extern_weak global
-
-// Case 2: @class first, then @interface (with availability).
-// This order already worked before the fix because @interface becomes
-// getMostRecentDecl() and carries the availability attribute.
-// We test it here to ensure the fix doesn't regress this case.
-
- at class WeakRedecl2;
-
-__attribute__((availability(ios,introduced=14.0)))
- at interface WeakRedecl2
- at end
-
- at implementation WeakRedecl2 (TestCategory2)
- at end
-
-// CHECK: @"OBJC_CLASS_$_WeakRedecl2" = extern_weak global
-
-// Case 3: Single declaration with availability (baseline, no redeclaration).
-__attribute__((availability(ios,introduced=14.0)))
- at interface WeakSingle
- at end
-
- at implementation WeakSingle (TestCategory3)
- at end
-
-// CHECK: @"OBJC_CLASS_$_WeakSingle" = extern_weak global
diff --git a/clang/test/Modules/Inputs/availability-redecl-weak/forward.h b/clang/test/Modules/Inputs/availability-redecl-weak/forward.h
new file mode 100644
index 0000000000000..c9123d49b7d99
--- /dev/null
+++ b/clang/test/Modules/Inputs/availability-redecl-weak/forward.h
@@ -0,0 +1 @@
+ at class WeakRedecl1;
diff --git a/clang/test/Modules/Inputs/availability-redecl-weak/interface.h b/clang/test/Modules/Inputs/availability-redecl-weak/interface.h
new file mode 100644
index 0000000000000..9de6f4aaa30e2
--- /dev/null
+++ b/clang/test/Modules/Inputs/availability-redecl-weak/interface.h
@@ -0,0 +1,8 @@
+// Mimics a class like UTType that has availability attrs for multiple platforms.
+// The 'macos' attr comes before 'ios', so getAttr<AvailabilityAttr>() returns
+// 'macos' first. When mergeInheritableAttributes copies only the first attr
+// across PCM boundaries, the 'ios' attr is lost on the @class redeclaration.
+__attribute__((availability(macos,introduced=11.0)))
+__attribute__((availability(ios,introduced=14.0)))
+ at interface WeakRedecl1
+ at end
diff --git a/clang/test/Modules/Inputs/availability-redecl-weak/module.modulemap b/clang/test/Modules/Inputs/availability-redecl-weak/module.modulemap
new file mode 100644
index 0000000000000..0123708ab26cd
--- /dev/null
+++ b/clang/test/Modules/Inputs/availability-redecl-weak/module.modulemap
@@ -0,0 +1,2 @@
+module InterfaceMod { header "interface.h" export * }
+module ForwardMod { header "forward.h" export * }
diff --git a/clang/test/Modules/availability-redecl-weak.m b/clang/test/Modules/availability-redecl-weak.m
new file mode 100644
index 0000000000000..1f093e2a8b3e6
--- /dev/null
+++ b/clang/test/Modules/availability-redecl-weak.m
@@ -0,0 +1,39 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -triple arm64-apple-ios12.0 -fmodules-cache-path=%t \
+// RUN: -fmodules -fimplicit-module-maps \
+// RUN: -I %S/Inputs/availability-redecl-weak \
+// RUN: -DINTERFACE_FIRST -emit-llvm -o - %s | FileCheck %s
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -triple arm64-apple-ios12.0 -fmodules-cache-path=%t \
+// RUN: -fmodules -fimplicit-module-maps \
+// RUN: -I %S/Inputs/availability-redecl-weak \
+// RUN: -emit-llvm -o - %s | FileCheck %s
+
+// Test that isWeakImported() traverses the redeclaration chain across module
+// boundaries to find availability attributes.
+//
+// InterfaceMod has @interface WeakRedecl1 with availability(macos,introduced=11.0)
+// and availability(ios,introduced=14.0). ForwardMod has a bare @class WeakRedecl1.
+//
+// When InterfaceMod is imported first and ForwardMod second, the @class becomes
+// getMostRecentDecl(). Cross-PCM mergeInheritableAttributes only copies the first
+// AvailabilityAttr (macos), losing the ios attr. The old isWeakImported() only
+// checked getMostRecentDecl()->attrs(), found only macos (not the ios target
+// platform), and incorrectly returned false (strong linkage).
+
+#ifdef INTERFACE_FIRST
+// This order triggers the bug: @interface loaded first, then @class becomes
+// the most recent decl with only an inherited macos availability attr.
+ at import InterfaceMod;
+ at import ForwardMod;
+#else
+// This order works even without the fix: @class loaded first, then @interface
+// becomes the most recent decl with all availability attrs intact.
+ at import ForwardMod;
+ at import InterfaceMod;
+#endif
+
+ at implementation WeakRedecl1 (TestCategory1)
+ at end
+
+// CHECK: @"OBJC_CLASS_$_WeakRedecl1" = extern_weak global
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