Fix bug where types other than 'cv auto', 'cv auto &', and 'cv auto &&' could

incorrectly be deduced from an initializer list in pathological cases.

llvm-svn: 291191

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -4127,6 +4127,12 @@ Sema::DeduceAutoType(TypeLoc Type, Expr *&Init, QualType &Result,
 
   InitListExpr *InitList = dyn_cast<InitListExpr>(Init);
   if (InitList) {
+    // Notionally, we substitute std::initializer_list<T> for 'auto' and deduce
+    // against that. Such deduction only succeeds if removing cv-qualifiers and
+    // references results in std::initializer_list<T>.
+    if (!Type.getType().getNonReferenceType()->getAs<AutoType>())
+      return DAR_Failed;
+
     for (unsigned i = 0, e = InitList->getNumInits(); i < e; ++i) {
       if (DeduceTemplateArgumentsFromCallArgument(
               *this, TemplateParamsSt.get(), TemplArg, InitList->getInit(i),

clang/test/SemaCXX/cxx0x-initializer-stdinitializerlist.cpp

@@ -337,3 +337,13 @@ namespace update_rbrace_loc_crash {
     Explode<ContainsIncomplete, 4>([](int) {});
   }
 }
+
+namespace no_conversion_after_auto_list_deduction {
+  // We used to deduce 'auto' == 'std::initializer_list<X>' here, and then
+  // incorrectly accept the declaration of 'x'.
+  struct X { using T = std::initializer_list<X> X::*; operator T(); };
+  auto X::*x = { X() }; // expected-error {{from initializer list}}
+
+  struct Y { using T = std::initializer_list<Y>(*)(); operator T(); };
+  auto (*y)() = { Y() }; // expected-error {{from initializer list}}
+}