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libstdc++: Define type traits for wchar_t even when libc support missing

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This meets the requirement that std::is_integral_v<wchar_t> is true,
even when full library support for wchar_t via specializations of
char_traits etc. is not provided. This is done by checking
__WCHAR_TYPE__ to see if the compiler knows about the type, rather than
checking the library's own _GLIBCXX_USE_WCHAR_T autoconf macro.

This assumes that the C++ compiler correctly defines wchar_t as a
distinct type, not a typedef for one of the other integeral types. This
is always true for G++ and should be true for any supported non-GNU
compilers.

Similarly, the std::make_unsigned and std::make_signed traits and the
internal helpers std::__is_integer and std::__is_char are also changed
to depend on the same macro.

libstdc++-v3/ChangeLog:

	* include/std/type_traits (is_integral<wchar_t>)
	(make_unsigned<wchar_t>, make_signed<wchar_t>): Define based
	on #ifdef __WCHAR_TYPE__ instead of _GLIBCXX_USE_WCHAR_T.
	* include/bits/cpp_type_traits.h (__is_integer<wchar_t>)
	(__is_char<wchar_t>): Likewise.
This commit is contained in:
Jonathan Wakely 2020-11-01 10:56:36 +00:00
parent de77abee11
commit 29e4184858
2 changed files with 8 additions and 5 deletions
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4
libstdc++-v3/include/bits/cpp_type_traits.h
View File

@ -162,7 +162,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
typedef __true_type __type;
};
# ifdef _GLIBCXX_USE_WCHAR_T
# ifdef __WCHAR_TYPE__
template<>
struct __is_integer<wchar_t>
{
@ -363,7 +363,7 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
typedef __true_type __type;
};
#ifdef _GLIBCXX_USE_WCHAR_T
#ifdef __WCHAR_TYPE__
template<>
struct __is_char<wchar_t>
{

9
libstdc++-v3/include/std/type_traits
View File

@ -269,7 +269,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
struct __is_integral_helper<unsigned char>
: public true_type { };
#ifdef _GLIBCXX_USE_WCHAR_T
// We want is_integral<wchar_t> to be true (and make_signed/unsigned to work)
// even when libc doesn't provide working <wchar.h> and related functions,
// so check __WCHAR_TYPE__ instead of _GLIBCXX_USE_WCHAR_T.
#ifdef __WCHAR_TYPE__
template<>
struct __is_integral_helper<wchar_t>
: public true_type { };
@ -1742,7 +1745,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// neither signed integer types nor unsigned integer types, so must be
// transformed to the unsigned integer type with the smallest rank.
// Use the partial specialization for enumeration types to do that.
#if defined(_GLIBCXX_USE_WCHAR_T)
#ifdef __WCHAR_TYPE__
template<>
struct __make_unsigned<wchar_t>
{
@ -1868,7 +1871,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// signed integer types nor unsigned integer types, so must be
// transformed to the signed integer type with the smallest rank.
// Use the partial specialization for enumeration types to do that.
#if defined(_GLIBCXX_USE_WCHAR_T)
#if defined(__WCHAR_TYPE__)
template<>
struct __make_signed<wchar_t>
{