[Sema] Fix bug in handling of designated initializer

[ahatanak]

Summary

CheckDesignatedInitializer wasn't taking into account the base classes when computing the index for the field in the derived class, which caused the test case to crash during IRGen because of a malformed AST.

[rnk]

What happens with virtual bases?

struct B { int x; };
struct D : virtual B { int y; };
void test() { D d = {1, .y = 2}; }

lib/Sema/SemaInit.cpp

2250 ↗

(On Diff #84390)

Do this before counting fields, IMO it's more intuitive.

test/SemaCXX/designated-initializers-base-class.cpp

1 ↗

(On Diff #84390)

This might be less fragile as an IRGen test. Alternatively, this is a good expected-no-diagnostic test:

void test() { D d = {1, .y = 2}; }

Right now we emit warning: initializer overrides prior initialization of this subobject, which is obviously wrong.

[ahatanak]

Address review comments.

[ahatanak]

In D28705#646088, @rnk wrote:

What happens with virtual bases?

struct B { int x; };
struct D : virtual B { int y; };
void test() { D d = {1, .y = 2}; }

A class with virtual base is not considered an aggregate, so it doesn't go through aggregate initialization (and therefore it doesn't enter CheckDesignatedInitializer). Instead, in TryListInitialization, it tries to find a matching constructor of D and fails.

test/SemaCXX/designated-initializers-base-class.cpp

1 ↗

(On Diff #84390)

good idea.

[arphaman]

LGTM

[rnk]

lgtm

cfe/trunk/lib/Sema/SemaInit.cpp

if (!KnownField) {
             << FieldName << CurrentObjectType;
           ++Index;
           return true;
         }
       }
     }
 
     unsigned FieldIndex = 0;
+
+    if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RT->getDecl()))
+      FieldIndex = CXXRD->getNumBases();
+
     for (auto *FI : RT->getDecl()->fields()) {
       if (FI->isUnnamedBitfield())
         continue;
       if (declaresSameEntity(KnownField, FI)) {
         KnownField = FI;
         break;
       }
       ++FieldIndex;

cfe/trunk/test/SemaCXX/designated-initializers-base-class.cpp

+// RUN: %clang_cc1 %s -std=c++1z -fsyntax-only -verify -Winitializer-overrides
+// expected-no-diagnostics
+
+struct B {
+  int x;
+};
+
+struct D : B {
+  int y;
+};
+
+void test() { D d = {1, .y = 2}; }