Fix ctype_byname<wchar_t>::do_is() mask checking.... again

This basically reverts the revert in r216508, and fixes a few more cases while
I'm at it. Reading my commit message on that commit again, I think it's bupkis.

http://reviews.llvm.org/D8237


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@231940 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/localization/locale.categories/category.ctype/locale.ctype.byname/mask.pass.cpp

@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <locale>
+
+// template <class charT> class ctype_byname;
+
+// bool is(mask m, charT c) const;
+
+#include <locale>
+#include <type_traits>
+#include <cassert>
+
+int main()
+{
+    {
+        std::locale l("C");
+        {
+            typedef std::ctype<wchar_t> WF;
+            const WF& wf = std::use_facet<WF>(l);
+            typedef std::ctype<char> CF;
+            const CF& cf = std::use_facet<CF>(l);
+
+            // The ctype masks in Newlib don't form a proper bitmask because
+            // the mask is only 8 bits wide, and there are more than 8 mask
+            // kinds. This means that the mask for alpha is (_U | _L), which
+            // is tricky to match in the do_is implementation because in
+            // [22.4.1.1.2 2] the standard specifies that the match code behaves
+            // like (m & M) != 0, but following this exactly would give false
+            // positives for characters that are both 'upper' and 'alpha', but
+            // not 'lower', for example.
+            assert( wf.is(WF::upper, L'A'));
+            assert( cf.is(CF::upper,  'A'));
+            assert(!wf.is(WF::lower, L'A'));
+            assert(!cf.is(CF::lower,  'A'));
+            assert( wf.is(WF::alpha, L'A'));
+            assert( cf.is(CF::alpha,  'A'));
+
+            assert(!wf.is(WF::upper, L'a'));
+            assert(!cf.is(CF::upper,  'a'));
+            assert( wf.is(WF::lower, L'a'));
+            assert( cf.is(CF::lower,  'a'));
+            assert( wf.is(WF::alpha, L'a'));
+            assert( cf.is(CF::alpha,  'a'));
+        }
+    }
+}