When importing classes and structs with anonymous structs, it is critical that

distinct anonymous structs remain distinct despite having similar layout.

This is already ensured by distinguishing based on their placement in the parent
struct, using the function `findAnonymousStructOrUnionIndex`.

The problem is that this function only handles anonymous structs, like
```
class Foo { struct { int a; } }
```
and not untagged structs like
```
class Foo { struct { int a; } var; }
```
Both need to be handled, and this patch fixes that.  The test case ensures that this functionality doesn't regress.

Thanks to Manman Ren for review.

https://reviews.llvm.org/D22270

llvm-svn: 275460

clang/lib/AST/ASTImporter.cpp

@@ -1029,7 +1029,7 @@ static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
 /// including the next assigned index (if none of them match). Returns an
 /// empty option if the context is not a record, i.e.. if the anonymous
 /// struct/union is at namespace or block scope.
-static Optional<unsigned> findAnonymousStructOrUnionIndex(RecordDecl *Anon) {
+static Optional<unsigned> findUntaggedStructOrUnionIndex(RecordDecl *Anon) {
   ASTContext &Context = Anon->getASTContext();
   QualType AnonTy = Context.getRecordType(Anon);
 
@@ -1040,13 +1040,29 @@ static Optional<unsigned> findAnonymousStructOrUnionIndex(RecordDecl *Anon) {
   unsigned Index = 0;
   for (const auto *D : Owner->noload_decls()) {
     const auto *F = dyn_cast<FieldDecl>(D);
-    if (!F || !F->isAnonymousStructOrUnion())
+    if (!F)
       continue;
 
-    if (Context.hasSameType(F->getType(), AnonTy))
-      break;
+    if (F->isAnonymousStructOrUnion()) {
+      if (Context.hasSameType(F->getType(), AnonTy))
+        break;
+      ++Index;
+      continue;
+    }
 
-    ++Index;
+    // If the field looks like this:
+    // struct { ... } A;
+    QualType FieldType = F->getType();
+    if (const auto *RecType = dyn_cast<RecordType>(FieldType)) {
+      const RecordDecl *RecDecl = RecType->getDecl();
+      if (RecDecl->getDeclContext() == Owner &&
+          !RecDecl->getIdentifier()) {
+        if (Context.hasSameType(FieldType, AnonTy))
+          break;
+        ++Index;
+        continue;
+      }
+    }
   }
 
   return Index;
@@ -1068,8 +1084,8 @@ static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
   if (D1->isAnonymousStructOrUnion() && D2->isAnonymousStructOrUnion()) {
     // If both anonymous structs/unions are in a record context, make sure
     // they occur in the same location in the context records.
-    if (Optional<unsigned> Index1 = findAnonymousStructOrUnionIndex(D1)) {
-      if (Optional<unsigned> Index2 = findAnonymousStructOrUnionIndex(D2)) {
+    if (Optional<unsigned> Index1 = findUntaggedStructOrUnionIndex(D1)) {
+      if (Optional<unsigned> Index2 = findUntaggedStructOrUnionIndex(D2)) {
         if (*Index1 != *Index2)
           return false;
       }
@@ -2749,9 +2765,9 @@ Decl *ASTNodeImporter::VisitRecordDecl(RecordDecl *D) {
           // If both anonymous structs/unions are in a record context, make sure
           // they occur in the same location in the context records.
           if (Optional<unsigned> Index1
-              = findAnonymousStructOrUnionIndex(D)) {
+              = findUntaggedStructOrUnionIndex(D)) {
             if (Optional<unsigned> Index2 =
-                    findAnonymousStructOrUnionIndex(FoundRecord)) {
+                    findUntaggedStructOrUnionIndex(FoundRecord)) {
               if (*Index1 != *Index2)
                 continue;
             }

clang/test/ASTMerge/Inputs/anonymous-fields1.cpp

@@ -0,0 +1,5 @@
+class A {
+public:
+  struct { int foo; } f;
+  struct { int foo; } g;
+};

clang/test/ASTMerge/Inputs/anonymous-fields2.cpp

@@ -0,0 +1,9 @@
+class A {
+public:
+  struct { int foo; } f;
+  struct { int foo; } g;
+};
+
+inline int useA(A &a) {
+  return (a.f.foo + a.g.foo);
+}

clang/test/ASTMerge/anonymous-fields.cpp

@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -emit-pch -o %t.1.ast %S/Inputs/anonymous-fields1.cpp
+// RUN: %clang_cc1 -emit-pch -o %t.2.ast %S/Inputs/anonymous-fields2.cpp
+// RUN: %clang_cc1 -emit-obj -o /dev/null -ast-merge %t.1.ast -ast-merge %t.2.ast %s
+// expected-no-diagnostics