[API Notes] Allow tag-based API notes on anonymous tag decls with typedef names

It is common practice in C to declare anonymous tags that are
immediately given a typedef name, e.g.,

    typedef enum { ... } MyType;

At present, one can only express API notes on the typedef. However, that
excludes the possibility of tag-specific notes like EnumExtensibility.
For these anonymous declarations, process API notes using the typedef
name as the tag name, so that one can add API notes to `MyType` via
the `Tags` section.

(cherry picked from commit 5e56bb2)

Author: DougGregor

clang/lib/Sema/SemaAPINotes.cpp

@@ -906,7 +906,15 @@ void Sema::ProcessAPINotes(Decl *D) {
 
     // Tags
     if (auto Tag = dyn_cast<TagDecl>(D)) {
-      std::string LookupName = Tag->getName().str();
+      // Determine the name of the entity to search for. If this is an
+      // anonymous tag that gets its linked name from a typedef, look for the
+      // typedef name. This allows tag-specific information to be added
+      // to the declaration.
+      std::string LookupName;
+      if (auto typedefName = Tag->getTypedefNameForAnonDecl())
+        LookupName = typedefName->getName().str();
+      else
+        LookupName = Tag->getName().str();
 
       // Use the source location to discern if this Tag is an OPTIONS macro.
       // For now we would like to limit this trick of looking up the APINote tag

clang/lib/Sema/SemaDecl.cpp

@@ -5026,6 +5026,9 @@ void Sema::setTagNameForLinkagePurposes(TagDecl *TagFromDeclSpec,
 
   // Otherwise, set this as the anon-decl typedef for the tag.
   TagFromDeclSpec->setTypedefNameForAnonDecl(NewTD);
+
+  // Now that we have a name for the tag, process API notes again.
+  ProcessAPINotes(TagFromDeclSpec);
 }
 
 static unsigned GetDiagnosticTypeSpecifierID(DeclSpec::TST T) {

clang/test/APINotes/Inputs/Frameworks/SimpleKit.framework/Headers/SimpleKit.apinotes

@@ -46,3 +46,5 @@ Tags:
     SwiftName:       SuccessfullyRenamedA
   - Name:            RenamedAgainInAPINotesB
     SwiftName:       SuccessfullyRenamedB
+  - Name:            AnonEnumWithTypedefName
+    SwiftName:       SuccessfullyRenamedC

clang/test/APINotes/Inputs/Frameworks/SimpleKit.framework/Headers/SimpleKit.h

@@ -27,3 +27,7 @@ void *getCFAuditedToNone_DUMP(void);
 - (id)getOwnedToUnowned __attribute__((__ns_returns_retained__));
 - (id)getUnownedToOwned __attribute__((__ns_returns_not_retained__));
 @end
+
+typedef enum {
+  kConstantInAnonEnum
+} AnonEnumWithTypedefName;

clang/test/APINotes/types.m

@@ -7,6 +7,9 @@
 
 // CHECK: struct __attribute__((swift_name("SuccessfullyRenamedA"))) RenamedAgainInAPINotesA {
 // CHECK: struct __attribute__((swift_name("SuccessfullyRenamedB"))) RenamedAgainInAPINotesB {
+// CHECK: typedef enum __attribute__((swift_name("SuccessfullyRenamedC"))) {
+// CHECK-NEXT: kConstantInAnonEnum
+// CHECK-NEXT: } AnonEnumWithTypedefName
 
 void test(OverriddenTypes *overridden) {
   int *ip1 = global_int_ptr; // expected-warning{{incompatible pointer types initializing 'int *' with an expression of type 'double (*)(int, int)'}}

clang/test/APINotes/yaml-roundtrip-2.test

@@ -7,5 +7,5 @@ REQUIRES: shell
 
 We expect only the document markers to be emitted
 
-CHECK: 50d
+CHECK: 52d
 CHECK: 1d