[PATCH] PR libstdc++/90281 Fix string conversions for filesystem::path

[Jonathan Wakely]

On 30/04/19 16:06 +0100, Jonathan Wakely wrote:
>Fix several bugs in the encoding conversions for filesystem::path that
>prevent conversion of Unicode characters outside the Basic Multilingual
>Plane, and prevent returning basic_string specializations with
>alternative allocator types.
>
>The std::codecvt_utf8 class template is not suitable for UTF-16
>conversions because it uses UCS-2 instead. For conversions between UTF-8
>and UTF-16 either std::codecvt<C, char, mbstate> or
>codecvt_utf8_utf16<C> must be used.
>
>The __str_codecvt_in and __str_codecvt_out utilities do not
>return false on a partial conversion (e.g. for invalid or incomplete
>Unicode input). Add new helpers that treat partial conversions as
>errors, and use them for all filesystem::path conversions.
>
>	PR libstdc++/90281 Fix string conversions for filesystem::path
>	* include/bits/fs_path.h (u8path) [_GLIBCXX_FILESYSTEM_IS_WINDOWS]:
>	Use codecvt_utf8_utf16 instead of codecvt_utf8. Use
>	__str_codecvt_in_all to fail for partial conversions and throw on
>	error.
>	[!_GLIBCXX_FILESYSTEM_IS_WINDOWS && _GLIBCXX_USE_CHAR8_T]
>	(path::_Cvt<char8_t>): Add explicit specialization.
>	[_GLIBCXX_FILESYSTEM_IS_WINDOWS] (path::_Cvt::_S_wconvert): Remove
>	overloads.
>	[_GLIBCXX_FILESYSTEM_IS_WINDOWS] (path::_Cvt::_S_convert): Use
>	if-constexpr instead of dispatching to _S_wconvert. Use codecvt
>	instead of codecvt_utf8. Use __str_codecvt_in_all and
>	__str_codecvt_out_all.
>	[!_GLIBCXX_FILESYSTEM_IS_WINDOWS] (path::_Cvt::_S_convert): Use
>	codecvt instead of codecvt_utf8. Use __str_codecvt_out_all.
>	(path::_S_str_convert) [_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Use
>	codecvt_utf8_utf16 instead of codecvt_utf8. Construct return values
>	with allocator. Use __str_codecvt_out_all. Fallthrough to POSIX code
>	after converting to UTF-8.
>	(path::_S_str_convert): Use codecvt instead of codecvt_utf8. Use
>	__str_codecvt_in_all.
>	(path::string): Fix initialization of string types with different
>	allocators.
>	(path::u8string) [_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Use
>	codecvt_utf8_utf16 instead of codecvt_utf8. Use __str_codecvt_out_all.
>	* include/bits/locale_conv.h (__do_str_codecvt): Reorder static and
>	runtime conditions.
>	(__str_codecvt_out_all, __str_codecvt_in_all): New functions that
>	return false for partial conversions.
>	* include/experimental/bits/fs_path.h (u8path):
>	[_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Implement correctly for mingw.
>	[_GLIBCXX_FILESYSTEM_IS_WINDOWS] (path::_Cvt::_S_wconvert): Add
>	missing handling for char8_t. Use codecvt and codecvt_utf8_utf16
>	instead of codecvt_utf8. Use __str_codecvt_in_all and
>	__str_codecvt_out_all.
>	[!_GLIBCXX_FILESYSTEM_IS_WINDOWS] (path::_Cvt::_S_convert): Use
>	codecvt instead of codecvt_utf8. Use __str_codecvt_out_all.
>	(path::string) [_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Use
>	codecvt_utf8_utf16 instead of codecvt_utf8. Construct return values
>	with allocator. Use __str_codecvt_out_all and __str_codecvt_in_all.
>	(path::string) [!_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Use
>	__str_codecvt_in_all.
>	(path::u8string) [_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Use
>	codecvt_utf8_utf16 instead of codecvt_utf8. Use __str_codecvt_out_all.
>	* src/c++17/fs_path.cc (path::_S_convert_loc): Use
>	__str_codecvt_in_all.
>	* src/filesystem/path.cc (path::_S_convert_loc): Likewise.
>	* testsuite/27_io/filesystem/path/construct/90281.cc: New test.
>	* testsuite/27_io/filesystem/path/factory/u8path.cc: New test.
>	* testsuite/27_io/filesystem/path/native/string.cc: Test with empty
>	strings and with Unicode characters outside the basic multilingual
>	plane.
>	* testsuite/27_io/filesystem/path/native/alloc.cc: New test.
>	* testsuite/experimental/filesystem/path/construct/90281.cc: New test.
>	* testsuite/experimental/filesystem/path/factory/u8path.cc: New test.
>	* testsuite/experimental/filesystem/path/native/alloc.cc: New test.
>	* testsuite/experimental/filesystem/path/native/string.cc: Test with
>	empty strings and with Unicode characters outside the basic
>	multilingual plane.
>
>Tested powerpc64le-linux and x86_64-w64-mingw32.
>
>As this ended up being a large patch I'll wait until after 9.1.0 is
>released to commit this (and then will backport a simpler version).

I forgot to commit the patch after the release. It's now on trunk, as
r272385, and I'll backport it soon.