[modules] Make IndirectFieldDecl mergeable to avoid lookup ambiguity when the same anonymous union is defined across multiple modules.

llvm-svn: 243940

clang/include/clang/AST/Decl.h

@@ -2499,7 +2499,8 @@ public:
 /// IndirectFieldDecl - An instance of this class is created to represent a
 /// field injected from an anonymous union/struct into the parent scope.
 /// IndirectFieldDecl are always implicit.
-class IndirectFieldDecl : public ValueDecl {
+class IndirectFieldDecl : public ValueDecl,
+                          public Mergeable<IndirectFieldDecl> {
   void anchor() override;
   NamedDecl **Chaining;
   unsigned ChainingSize;
@@ -2537,6 +2538,9 @@ public:
     return dyn_cast<VarDecl>(*chain_begin());
   }
 
+  IndirectFieldDecl *getCanonicalDecl() override { return getFirstDecl(); }
+  const IndirectFieldDecl *getCanonicalDecl() const { return getFirstDecl(); }
+
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == IndirectField; }

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -1178,6 +1178,8 @@ void ASTDeclReader::VisitIndirectFieldDecl(IndirectFieldDecl *FD) {
 
   for (unsigned I = 0; I != FD->ChainingSize; ++I)
     FD->Chaining[I] = ReadDeclAs<NamedDecl>(Record, Idx);
+
+  mergeMergeable(FD);
 }
 
 ASTDeclReader::RedeclarableResult ASTDeclReader::VisitVarDeclImpl(VarDecl *VD) {
@@ -2638,6 +2640,13 @@ static bool isSameEntity(NamedDecl *X, NamedDecl *Y) {
     return X->getASTContext().hasSameType(FDX->getType(), FDY->getType());
   }
 
+  // Indirect fields with the same target field match.
+  if (auto *IFDX = dyn_cast<IndirectFieldDecl>(X)) {
+    auto *IFDY = cast<IndirectFieldDecl>(Y);
+    return IFDX->getAnonField()->getCanonicalDecl() ==
+           IFDY->getAnonField()->getCanonicalDecl();
+  }
+
   // Enumerators with the same name match.
   if (isa<EnumConstantDecl>(X))
     // FIXME: Also check the value is odr-equivalent.

clang/test/Modules/Inputs/submodules-merge-defs/defs.h

@@ -103,3 +103,11 @@ namespace RedeclDifferentDeclKind {
   typedef X X;
   using RedeclDifferentDeclKind::X;
 }
+
+namespace Anon {
+  struct X {
+    union {
+      int n;
+    };
+  };
+}

clang/test/Modules/submodules-merge-defs.cpp

@@ -104,6 +104,7 @@ template<typename T, int N, template<typename> class K> struct J;
 J<> post_j2;
 FriendDefArg::Y<int> friend_def_arg;
 FriendDefArg::D<> friend_def_arg_d;
+int post_anon_x_n = Anon::X().n;
 
 MergeFunctionTemplateSpecializations::X<int>::Q<char> xiqc;