From 169417531578501e955f12c79ecb8ff05333ae15 Mon Sep 17 00:00:00 2001
From: Michael Spencer <bigcheesegs@gmail.com>
Date: Wed, 15 Jun 2022 17:45:51 -0700
Subject: [PATCH] [Clang][Modules] Merge availability attributes on imported
 decls

Currently we do not in general merge attributes when importing decls from modules. This patch handles availability, but long term we need to properly handle all attributes.

I tried to use Sema::mergeDeclAttributes, but it caused test crashes as I don't think it expects to be called in this context. We really shouldn't have duplicate code for merging attributes long term, but for now this fixes availability. There's already a TODO for this in the declaration of ASTDeclReader::mergeInheritableAttributes.

Differential Revision: https://reviews.llvm.org/D127182

rdar://85820301
---
 clang/lib/Serialization/ASTReaderDecl.cpp |  7 ++++
 clang/test/Modules/decl-attr-merge.mm     | 41 +++++++++++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 clang/test/Modules/decl-attr-merge.mm

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 86a9c7733069..ae298557ee49 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -3296,6 +3296,13 @@ void ASTDeclReader::mergeInheritableAttributes(ASTReader &Reader, Decl *D,
     NewAttr->setInherited(true);
     D->addAttr(NewAttr);
   }
+
+  const auto *AA = Previous->getAttr<AvailabilityAttr>();
+  if (AA && !D->hasAttr<AvailabilityAttr>()) {
+    NewAttr = AA->clone(Context);
+    NewAttr->setInherited(true);
+    D->addAttr(NewAttr);
+  }
 }
 
 template<typename DeclT>
diff --git a/clang/test/Modules/decl-attr-merge.mm b/clang/test/Modules/decl-attr-merge.mm
new file mode 100644
index 000000000000..57f3f93df480
--- /dev/null
+++ b/clang/test/Modules/decl-attr-merge.mm
@@ -0,0 +1,41 @@
+// RUN: rm -rf %t.dir
+// RUN: split-file %s %t.dir
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps \
+// RUN:   -fmodules-cache-path=%t.dir/cache -triple x86_64-apple-macosx10.11.0 \
+// RUN:   -I%t.dir/headers %t.dir/main.m -emit-llvm -o %t.dir/main.ll
+// RUN: cat %t.dir/main.ll | FileCheck %s
+
+//--- headers/a.h
+
+__attribute__((availability(macos,introduced=10.16)))
+@interface INIntent
+- (instancetype)self;
+@end
+
+//--- headers/b.h
+
+@class INIntent;
+
+//--- headers/module.modulemap
+
+module A {
+  header "a.h"
+}
+
+module B {
+  header "b.h"
+}
+
+//--- main.m
+
+#import <a.h>
+#import <b.h> // NOTE: Non attributed decl imported after one with attrs.
+
+void F(id);
+
+int main() {
+  if (@available(macOS 11.0, *))
+    F([INIntent self]);
+}
+
+// CHECK: @"OBJC_CLASS_$_INIntent" = extern_weak