[clang] [Clang] Fix isWeakImported() to traverse redeclaration chain for avai… (PR #181482)

[via cfe-commits]

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@@ -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.
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kevinlzh1108 wrote:

Done. I've narrowed the change to only ASTReaderDecl.cpp and updated the test:

  - **Dropped DeclBase.cpp** — as you pointed out, the Sema path already handles this correctly via `mergeDeclAttributes` + `specific_attrs<InheritableAttr>()`. The PCM path is the only one that needs fixing.
  - **Extended `decl-attr-merge.mm`** instead of adding a new test file — added `availability(ios, introduced=14.0)` to the existing `@interface INIntent` and an iOS triple RUN line. Without the fix, `mergeInheritableAttributes`
  copies only the first (macOS) attr and drops the iOS one, causing `isWeakImported()` to return false. With the fix, both platform attrs are propagated and the symbol is correctly `extern_weak`.

  The PR is now a single fix in `mergeInheritableAttributes` + a test extension.

https://github.com/llvm/llvm-project/pull/181482