[modules] While merging ObjCInterfaceDecl definitions, merge them as decl contexts too.

While working on https://reviews.llvm.org/D110280 I've tried to merge
decl contexts as it seems to be correct and matching our handling of
decl contexts from different modules. It's not required for the fix in
https://reviews.llvm.org/D110280 but it revealed a missing diagnostic,
so separating this change into a separate commit.

Renamed some variables to distinguish diagnostic like "declaration of
'x' does not match" for different cases.

Differential Revision: https://reviews.llvm.org/D110287

(cherry picked from commit c593126)

Author: vsapsai

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -1149,6 +1149,12 @@ void ASTDeclReader::ReadObjCDefinitionData(
 
 void ASTDeclReader::MergeDefinitionData(ObjCInterfaceDecl *D,
          struct ObjCInterfaceDecl::DefinitionData &&NewDD) {
+  struct ObjCInterfaceDecl::DefinitionData &DD = D->data();
+  if (DD.Definition != NewDD.Definition) {
+    Reader.MergedDeclContexts.insert(
+        std::make_pair(NewDD.Definition, DD.Definition));
+  }
+
   // FIXME: odr checking?
 }
 

clang/test/Modules/odr_hash.mm

@@ -241,12 +241,12 @@ @interface Interface4 <T : I1 *> {
 @end
 @interface Interface5 <T : I1 *> {
 @public
-  T x; // FIXME: align with upstream (rdar://43906928).
+  T y; // FIXME: align with upstream (rdar://43906928).
 }
 @end
 @interface Interface6 <T1 : I1 *, T2 : I2 *> {
 @public
-  T1 x;
+  T1 z;
 }
 @end
 #elif defined(SECOND)
@@ -257,14 +257,17 @@ @interface Interface4 <T : I1 *> {
 @end
 @interface Interface5 <T : I1 *> {
 @public
-  T x; // FIXME: align with upstream (rdar://43906928).
+  T y; // FIXME: align with upstream (rdar://43906928).
 }
 @end
 @interface Interface6 <T1 : I1 *, T2 : I2 *> {
 @public
-  T2 x;
+  T2 z;
 }
 @end
+#else
+// [email protected]:* {{'Interface6::z' from module 'FirstModule' is not present in definition of 'Interface6' in module 'SecondModule'}}
+// [email protected]:* {{declaration of 'z' does not match}}
 #endif
 
 namespace Types {
@@ -276,18 +279,18 @@ @interface Interface6 <T1 : I1 *, T2 : I2 *> {
 };
 struct Invalid2 {
   Interface5 *I;
-  decltype(I->x) x;
+  decltype(I->y) y;
 };
 struct Invalid3 {
   Interface6 *I;
-  decltype(I->x) x;
+  decltype(I->z) z;
 };
 #else
 Invalid1 i1;
 Invalid2 i2;
 Invalid3 i3;
-// [email protected]:* {{'Types::ObjCTypeParam::Invalid3::x' from module 'FirstModule' is not present in definition of 'Types::ObjCTypeParam::Invalid3' in module 'SecondModule'}}
-// [email protected]:* {{declaration of 'x' does not match}}
+// [email protected]:* {{'Types::ObjCTypeParam::Invalid3::z' from module 'FirstModule' is not present in definition of 'Types::ObjCTypeParam::Invalid3' in module 'SecondModule'}}
+// [email protected]:* {{declaration of 'z' does not match}}
 #endif
 
 }  // namespace ObjCTypeParam