Prevent Scoped Enums from being Integral constant expressions:

[erichkeane]

Summary

Discovered because of: https://bugs.llvm.org/show_bug.cgi?id=38235

It seems to me that a scoped enum should NOT be an integral constant expression
without a cast, so this seems like a sensical change. I very much want to hear
from a Core person however (@rsmith :) ).

[rsmith]

Seems fine to me (assuming we still accept the places that are supposed to allow a scoped enum, such as a case label).

cfe/trunk/lib/AST/ExprConstant.cpp

#include "clang/AST/StmtNodes.inc"
   llvm_unreachable("Invalid StmtClass!");
 }
 
 /// Evaluate an expression as a C++11 integral constant expression.
 static bool EvaluateCPlusPlus11IntegralConstantExpr(const ASTContext &Ctx,
                                                     const Expr *E,
                                                     llvm::APSInt *Value,
                                                     SourceLocation *Loc) {
-  if (!E->getType()->isIntegralOrEnumerationType()) {
+  if (!E->getType()->isIntegralOrUnscopedEnumerationType()) {
     if (Loc) *Loc = E->getExprLoc();
     return false;
   }
 
   APValue Result;
   if (!E->isCXX11ConstantExpr(Ctx, &Result, Loc))
     return false;
 

cfe/trunk/test/SemaCXX/PR38235.cpp

+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+enum class E { Foo, Bar = 97119 };
+
+void f() __attribute__((constructor(E::Foo))); // expected-error{{'constructor' attribute requires an integer constant}}
+void f2() __attribute__((constructor(E::Bar)));// expected-error{{'constructor' attribute requires an integer constant}}
+
+void switch_me(E e) {
+  switch (e) {
+    case E::Foo:
+    case E::Bar:
+      break;
+  }
+}