[API Notes] Attach API notes to forward declarations of tags

Forward declarations can still have useful API notes applied to them.
When the use of the tag is not a definition, apply the API notes
immediately.

Fixes rdar://156288588.

Author: DougGregor

clang/lib/Sema/SemaDecl.cpp

@@ -18476,6 +18476,10 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
   // record.
   AddPushedVisibilityAttribute(New);
 
+  // If this is not a definition, process API notes for it now.
+  if (TUK != TagUseKind::Definition)
+    ProcessAPINotes(New);
+
   if (isMemberSpecialization && !New->isInvalidDecl())
     CompleteMemberSpecialization(New, Previous);
 

clang/test/APINotes/Inputs/Headers/SwiftImportAs.apinotes

@@ -19,6 +19,10 @@ Tags:
   SwiftReleaseOp: release
   SwiftRetainOp: retain
   SwiftDefaultOwnership: unretained
+- Name: OpaqueRefCountedType
+  SwiftImportAs: reference
+  SwiftReleaseOp: ORCRelease
+  SwiftRetainOp: ORCRetain
 - Name: NonCopyableType
   SwiftCopyable: false
   SwiftConformsTo: MySwiftModule.MySwiftNonCopyableProtocol

clang/test/APINotes/Inputs/Headers/SwiftImportAs.h

@@ -23,3 +23,8 @@ struct EscapableType { int value; };
 struct RefCountedTypeWithDefaultConvention {};
 inline void retain(RefCountedType *x) {}
 inline void release(RefCountedType *x) {}
+
+struct OpaqueRefCountedType;
+
+inline void ORCRetain(struct OpaqueRefCountedType *x);
+inline void ORCRelease(struct OpaqueRefCountedType *x);

clang/test/APINotes/swift-import-as.cpp

@@ -3,6 +3,7 @@
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter ImmortalRefType | FileCheck -check-prefix=CHECK-IMMORTAL %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter RefCountedType | FileCheck -check-prefix=CHECK-REF-COUNTED %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter RefCountedTypeWithDefaultConvention | FileCheck -check-prefix=CHECK-REF-COUNTED-DEFAULT %s
+// RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter OpaqueRefCountedType | FileCheck -check-prefix=CHECK-OPAQUE-REF-COUNTED %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter NonCopyableType | FileCheck -check-prefix=CHECK-NON-COPYABLE %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter CopyableType | FileCheck -check-prefix=CHECK-COPYABLE %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter NonEscapableType | FileCheck -check-prefix=CHECK-NON-ESCAPABLE %s
@@ -34,6 +35,12 @@
 // CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> "release:release"
 // CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> "returned_as_unretained_by_default"
 
+// CHECK-OPAQUE-REF-COUNTED: Dumping OpaqueRefCountedType:
+// CHECK-OPAQUE-REF-COUNTED-NEXT: CXXRecordDecl {{.+}} imported in SwiftImportAs{{.*}}struct OpaqueRefCountedType
+// CHECK-OPAQUE-REF-COUNTED: SwiftAttrAttr {{.+}} <<invalid sloc>> "import_reference"
+// CHECK-OPAQUE-REF-COUNTED: SwiftAttrAttr {{.+}} <<invalid sloc>> "retain:ORCRetain"
+// CHECK-OPAQUE-REF-COUNTED: SwiftAttrAttr {{.+}} <<invalid sloc>> "release:ORCRelease"
+
 // CHECK-NON-COPYABLE: Dumping NonCopyableType:
 // CHECK-NON-COPYABLE-NEXT: CXXRecordDecl {{.+}} imported in SwiftImportAs {{.+}} struct NonCopyableType
 // CHECK-NON-COPYABLE: SwiftAttrAttr {{.+}} <<invalid sloc>> "conforms_to:MySwiftModule.MySwiftNonCopyableProtocol"