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

[via cfe-commits]

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@@ -3647,11 +3620,16 @@ void mergeInheritableAttributes(ASTReader &Reader, Decl *D, Decl *Previous) {
     D->addAttr(NewAttr);
   }
 
-  const auto *AA = Previous->getAttr<AvailabilityAttr>();
-  if (AA && !D->hasAttr<AvailabilityAttr>()) {
-    NewAttr = AA->clone(Context);
-    NewAttr->setInherited(true);
-    D->addAttr(NewAttr);
+  // getAttr<AvailabilityAttr>() only returns the first match, but a
+  // declaration can carry multiple AvailabilityAttrs (one per platform,
+  // e.g. macos + ios).  Iterate over all of them so every platform's
+  // availability is propagated to the new redeclaration.
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kevinlzh1108 wrote:

Done. Removed the comment and updated the commit message — the explanation now lives there instead. Thanks for the review!

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