[Sema] Implement LWG 2015 for the builtin type-traits.

[EricWF]

Summary

This patch implements LWG 2015, which requires than arrays used with [meta.unary.prop] traits have a complete element type.

Note that this patch should still diagnose the same cases as before, however the diagnostic now points to the base element type of an multi-dimensional array, instead of the array type itself.

If I'm not mistaken the correct thing to do is to retroactively apply it to C++11 even though it first appeared in the C++14 standard.

[aaron.ballman]

If I'm not mistaken the correct thing to do is to retroactively apply it to C++11 even though it first appeared in the C++14 standard.

That is how we typically handle DRs.

Do you also need to change the implementation of EvaluateBinaryTypeTrait() for the changes to is_base_of()?

lib/Sema/SemaExprCXX.cpp

4083–4084

Is this correct for has_virtual_destructor()? LWG 2015 treats that the same as is_empty() and friends.

[EricWF]

Woops. This may actually be entirely unneeded.

lib/Sema/SemaExprCXX.cpp

4083–4084

It's not correct. I'll update with a fix later this week.

lib/Sema/SemaExprCXX.cpp

   case UTT_HasNothrowConstructor:
   case UTT_HasNothrowCopy:
   case UTT_HasTrivialAssign:
   case UTT_HasTrivialMoveAssign:
   case UTT_HasTrivialDefaultConstructor:
   case UTT_HasTrivialMoveConstructor:
   case UTT_HasTrivialCopy:
   case UTT_HasTrivialDestructor:
   case UTT_HasVirtualDestructor:
-    // Arrays of unknown bound are expressly allowed.
-    QualType ElTy = ArgTy;
-    if (ArgTy->isIncompleteArrayType())
-      ElTy = S.Context.getAsArrayType(ArgTy)->getElementType();
+    // C++14 [meta.unary.prop]
+    //   remove_all_extents_t<T> shall be a complete type or
+    //   (possibly cv-qualified) void.
+    // See LWG 2015
+    QualType ElTy = S.Context.getBaseElementType(ArgTy);
 
     // The void type is expressly allowed.
     if (ElTy->isVoidType())
       return true;
 
     return !S.RequireCompleteType(
       Loc, ElTy, diag::err_incomplete_type_used_in_type_trait_expr);
   }

test/SemaCXX/type-traits-incomplete.cpp

 // RUN: %clang_cc1 -fsyntax-only -verify %s 
 
-struct S; // expected-note 2 {{forward declaration of 'S'}}
+struct S; // expected-note 4 {{forward declaration of 'S'}}
+typedef S SAr[10];
+typedef S SArNB[];
+typedef S SArMB[10][2];
 
 void f() {
   __is_pod(S); // expected-error{{incomplete type 'S' used in type trait expression}}
   __is_pod(S[]); // expected-error{{incomplete type 'S' used in type trait expression}}
+  __is_pod(S[10][2]); // expected-error{{incomplete type 'S' used in type trait expression}}
+  __is_pod(S[][10]); // expected-error{{incomplete type 'S' used in type trait expression}}
+  (void)__is_pod(void); // OK
+  (void)__is_pod(const volatile void); // OK
 }