PR20346: fix aggregate initialization / template instantiation bug:

If, during the initial parse of a template, we perform aggregate initialization
and form an implicit value initialization for an array type, then when we come
to instantiate the template and redo the initialization step, we would try to
match the implicit value initialization up against an array *element*, not to
the complete array.

Remarkably, we've had this bug since ~the dawn of time, but only noticed it
recently.

llvm-svn: 213332

clang/lib/Sema/SemaInit.cpp

@@ -914,6 +914,15 @@ void InitListChecker::CheckSubElementType(const InitializedEntity &Entity,
     assert(SemaRef.getLangOpts().CPlusPlus &&
            "non-aggregate records are only possible in C++");
     // C++ initialization is handled later.
+  } else if (auto *VIE = dyn_cast<ImplicitValueInitExpr>(expr)) {
+    // This happens during template instantiation when we see an InitListExpr
+    // that we've already checked once.
+    assert(SemaRef.Context.hasSameType(VIE->getType(), ElemType) &&
+           "found implicit initialization for the wrong type");
+    if (!VerifyOnly)
+      UpdateStructuredListElement(StructuredList, StructuredIndex, expr);
+    ++Index;
+    return;
   }
 
   // FIXME: Need to handle atomic aggregate types with implicit init lists.

clang/test/SemaTemplate/instantiate-decl-init.cpp

@@ -45,3 +45,23 @@ template<int N> void f1() {
   NonTrivial array[N];
 }
 template<> void f1<2>();
+
+namespace PR20346 {
+  struct S { short inner_s; };
+
+  struct outer_struct {
+    wchar_t arr[32];
+    S outer_s;
+  };
+
+  template <class T>
+  void OpenFileSession() {
+    // Ensure that we don't think the ImplicitValueInitExpr generated here
+    // during the initial parse only initializes the first array element!
+    outer_struct asdfasdf = {};
+  };
+
+  void foo() {
+    OpenFileSession<int>();
+  }
+}