Re: [PATCH v4] libstdc++: Implement C++26 std::text_encoding (P1885R12) [PR113318]

[Jonathan Wakely <jwakely@redhat.com>]

On Tue, 16 Jan 2024 at 15:39, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> On Tue, 16 Jan 2024 at 14:07, Jonathan Wakely wrote:
> >
> > On 15/01/24 19:09 -0500, Patrick Palka wrote:
> > >> +    friend _Iterator
> > >> +    operator+(_Iterator __i, difference_type __n)
> > >
> > >constexpr?
> >
> > Fixed. I've added tests that all iterator ops are usable in constant
> > expressions, which found a bug in operator+= (it didn't let you
> > increment one past the end of the range).
>
> I found another bug in operator+= which is fixed and tested like so:
>
> --- a/libstdc++-v3/include/std/text_encoding
> +++ b/libstdc++-v3/include/std/text_encoding
> @@ -584,7 +584,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>                *this == _Iterator{};
>            }
>        }
> -      __glibcxx_assert(_M_rep != nullptr);
> +      if (__n != 0)
> +       __glibcxx_assert(_M_rep != nullptr);
>       return *this;
>     }
>
> --- a/libstdc++-v3/testsuite/std/text_encoding/requirements.cc
> +++ b/libstdc++-v3/testsuite/std/text_encoding/requirements.cc
> @@ -67,6 +67,11 @@ test_constexpr_iterator()
>   VERIFY( *(iter + 1) == iter[1] );
>   VERIFY( (1 + iter - 1) == begin );
>   VERIFY( (-1 + (iter - -2) + -1) == begin );
> +
> +  std::ranges::iterator_t<std::text_encoding::aliases_view> singular;
> +  VERIFY( (singular + 0) == singular );
> +  VERIFY( (singular - 0) == singular );
> +
>   return true;
> }
> static_assert( test_constexpr_iterator() );


I'll also change this, after a suggestion from one of the paper
authors (Corentin):

--- a/libstdc++-v3/src/c++26/text_encoding.cc
+++ b/libstdc++-v3/src/c++26/text_encoding.cc
@@ -38,7 +38,7 @@ text_encoding
__locale_encoding(const char* name)
{
  text_encoding enc;
-  if (locale_t loc = ::newlocale(LC_ALL_MASK, name, (locale_t)0))
+  if (locale_t loc = ::newlocale(LC_CTYPE_MASK, name, (locale_t)0))
    {
      if (const char* codeset = ::nl_langinfo_l(CODESET, loc))
       {
@@ -64,7 +64,7 @@ bool
std::text_encoding::_M_is_environment() const
{
  bool matched = false;
-  if (locale_t loc = ::newlocale(LC_ALL_MASK, "", (locale_t)0))
+  if (locale_t loc = ::newlocale(LC_CTYPE_MASK, "", (locale_t)0))
    {
      if (const char* codeset = ::nl_langinfo_l(CODESET, loc))
       {