Fix crash in BuildCXXDefaultInitExpr.

[teemperor]

Summary

Fix crash in BuildCXXDefaultInitExpr when member of template class
has same name as the class itself.

[rnk]

lgtm

test/SemaCXX/pr27047-default-init-expr-name-conflict.cpp

6 ↗

(On Diff #55580)

More reduced:

template <typename T> struct A { int A = 0; };
A<int> a;

cfe/trunk/lib/Sema/SemaDeclCXX.cpp

ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
   // Maybe we haven't instantiated the in-class initializer. Go check the
   // pattern FieldDecl to see if it has one.
   CXXRecordDecl *ParentRD = cast<CXXRecordDecl>(Field->getParent());
 
   if (isTemplateInstantiation(ParentRD->getTemplateSpecializationKind())) {
     CXXRecordDecl *ClassPattern = ParentRD->getTemplateInstantiationPattern();
     DeclContext::lookup_result Lookup =
         ClassPattern->lookup(Field->getDeclName());
-    assert(Lookup.size() == 1);
-    FieldDecl *Pattern = cast<FieldDecl>(Lookup[0]);
+
+    // Lookup can return at most two results: the pattern for the field, or the
+    // injected class name of the parent record. No other member can have the
+    // same name as the field.
+    assert(!Lookup.empty() && Lookup.size() <= 2 &&
+           "more than two lookup results for field name");
+    FieldDecl *Pattern = dyn_cast<FieldDecl>(Lookup[0]);
+    if (!Pattern) {
+      assert(isa<CXXRecordDecl>(Lookup[0]) &&
+             "cannot have other non-field member with same name");
+      Pattern = cast<FieldDecl>(Lookup[1]);
+    }
+
     if (InstantiateInClassInitializer(Loc, Field, Pattern,
                                       getTemplateInstantiationArgs(Field)))
       return ExprError();
     return CXXDefaultInitExpr::Create(Context, Loc, Field);
   }
 
   // DR1351:
   //   If the brace-or-equal-initializer of a non-static data member

cfe/trunk/test/SemaCXX/pr27047-default-init-expr-name-conflict.cpp

+// RUN: %clang_cc1 -fsyntax-only -std=c++11 %s
+
+template <typename T>
+struct A {
+  // Used to crash when field was named after class.
+  int A = 0;
+};
+A<int> a;