[libc++] Implements isblank.

[Mordante]

Summary

This omission seems to be there for a long time, it's in the initial
libc++ import. This was discovered while working on the std modules.

[philnik]

Crazy that nobody complained about this in the past 10 years. LGTM.

libcxx/include/__locale

931–938

Maybe clang-format this?

libcxx/test/std/localization/locales/locale.convenience/classification/isblank.pass.cpp

21

Is \t also considered blank?

[Mordante]

In D147850#4253141, @philnik wrote:

Crazy that nobody complained about this in the past 10 years. LGTM.

Agreed, I even searched for a bug report, but there is none. Maybe it's a hint how popular locale support in C++ is ;-)

Thanks for the review!

libcxx/test/std/localization/locales/locale.convenience/classification/isblank.pass.cpp

21

It should be, but the list is not exhaustive, I did the same as for similar tests.

libcxx/include/__locale

 inline _LIBCPP_INLINE_VISIBILITY
 bool
 isgraph(_CharT __c, const locale& __loc)
 {
     return std::use_facet<ctype<_CharT> >(__loc).is(ctype_base::graph, __c);
 }
 
 template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI bool isblank(_CharT __c, const locale& __loc) {
+    return std::use_facet<ctype<_CharT> >(__loc).is(ctype_base::blank, __c);
+}
+
+template <class _CharT>
 inline _LIBCPP_INLINE_VISIBILITY
 _CharT
 toupper(_CharT __c, const locale& __loc)
 {
     return std::use_facet<ctype<_CharT> >(__loc).toupper(__c);
 }
 
 template <class _CharT>
 inline _LIBCPP_INLINE_VISIBILITY
 _CharT
 tolower(_CharT __c, const locale& __loc)

libcxx/test/std/localization/locales/locale.convenience/classification/isblank.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <locale>
+
+// template <class charT> bool isblank (charT c, const locale& loc);
+
+#include <locale>
+#include <cassert>
+
+#include "test_macros.h"
+
+int main(int, char**) {
+  std::locale l;
+  assert(std::isblank(' ', l));
+  assert(!std::isblank('<', l));
+  assert(!std::isblank('\x8', l));
+  assert(!std::isblank('A', l));
+  assert(!std::isblank('a', l));
+  assert(!std::isblank('z', l));
+  assert(!std::isblank('3', l));
+  assert(!std::isblank('.', l));
+  assert(!std::isblank('f', l));
+  assert(!std::isblank('9', l));
+  assert(!std::isblank('+', l));
+
+  return 0;
+}