libstdc++: Implement C++26 native handles for file streams (P1759R6)

The new __basic_file::native_handle() function can be added for C++11
and above, because the names "native_handle" and "native_handle_type"
are already reserved since C++11. Exporting those symbols from the
shared library does no harm, even if the feature gets dropped before the
C++23 standard is final.

The new member functions of std::fstream etc. are only declared for
C++26 and so are not instantiated in src/c++11/fstream-inst.cc. Declare
them with the always_inline attribute so that no symbol definitions are
needed in the library (we can change this later when C++26 support is
less experimental).

libstdc++-v3/ChangeLog:

	* acinclude.m4 (GLIBCXX_CHECK_FILEBUF_NATIVE_HANDLES): New
	macro.
	* config.h.in: Regenerate.
	* config/abi/pre/gnu.ver (GLIBCXX_3.4.32): Export new
	basic_filebuf members.
	* config/io/basic_file_stdio.cc (__basic_file::native_handle):
	Define new function.
	* config/io/basic_file_stdio.h (__basic_file::native_handle):
	Declare new function.
	* configure: Regenerate.
	* configure.ac: Use GLIBCXX_CHECK_FILEBUF_NATIVE_HANDLES.
	* include/bits/version.def (fstream_native_handles): New macro.
	* include/bits/version.h: Regenerate.
	* include/std/fstream (basic_filebuf::native_handle)
	(basic_fstream::native_handle, basic_ifstream::native_handle)
	(basic_ofstream::native_handle): New functions.
	* src/c++11/Makefile.am: Move compilation of basic_file.cc,
	locale_init.cc and localename.cc to here.
	* src/c++11/Makefile.in: Regenerate.
	* src/c++98/locale_init.cc: Moved to...
	* src/c++11/locale_init.cc: ...here.
	* src/c++98/localename.cc: Moved to...
	* src/c++11/localename.cc: ...here.
	* src/c++98/Makefile.am: Remove basic_file.cc, locale_init.cc
	and localename.cc from here.
	* src/c++98/Makefile.in: Regenerate.
	* testsuite/27_io/basic_filebuf/native_handle/version.cc: New test.
	* testsuite/27_io/basic_fstream/native_handle/char/1.cc: New test.
	* testsuite/27_io/basic_fstream/native_handle/wchar_t/1.cc: New test.
	* testsuite/27_io/basic_ifstream/native_handle/char/1.cc: New test.
	* testsuite/27_io/basic_ifstream/native_handle/wchar_t/1.cc: New test.
	* testsuite/27_io/basic_ofstream/native_handle/char/1.cc: New test.
	* testsuite/27_io/basic_ofstream/native_handle/wchar_t/1.cc: New test.

3 files changed, 33 insertions, 0 deletions

diff --git a/libstdc++-v3/config/abi/pre/gnu.ver b/libstdc++-v3/config/abi/pre/gnu.ver
index a2e5f3b..15b50d5 100644
--- a/libstdc++-v3/config/abi/pre/gnu.ver
+++ b/libstdc++-v3/config/abi/pre/gnu.ver
@@ -2519,6 +2519,8 @@ GLIBCXX_3.4.31 {
 GLIBCXX_3.4.32 {
     _ZSt21ios_base_library_initv;
     _ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE11_S_allocateERS3_[jmy];
+    # std::basic_file<>::native_handle()
+    _ZNKSt12__basic_fileI[cw]E13native_handleEv;
 } GLIBCXX_3.4.31;
 
 # Symbols in the support library (libsupc++) have their own tag.
diff --git a/libstdc++-v3/config/io/basic_file_stdio.cc b/libstdc++-v3/config/io/basic_file_stdio.cc
index 7b1729a..a33b53b 100644
--- a/libstdc++-v3/config/io/basic_file_stdio.cc
+++ b/libstdc++-v3/config/io/basic_file_stdio.cc
@@ -66,6 +66,11 @@
 
 #include <limits> // For <off_t>::max() and min() and <streamsize>::max()
 
+#if _GLIBCXX_USE__GET_OSFHANDLE
+# include <stdint.h> // For intptr_t
+# include <io.h>     // For _get_osfhandle
+#endif
+
 namespace
 {
   // Map ios_base::openmode flags to a string for use in fopen().
@@ -460,6 +465,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     return 0;
   }
 
+  __basic_file<char>::native_handle_type
+  __basic_file<char>::native_handle() const noexcept
+  {
+#ifdef _GLIBCXX_USE_STDIO_PURE
+    return _M_cfile;
+#elif _GLIBCXX_USE__GET_OSFHANDLE
+    const intptr_t handle = _M_cfile ? _get_osfhandle(fileno(_M_cfile)) : -1;
+    return reinterpret_cast<native_handle>(handle);
+#else
+    return fileno(_M_cfile);
+#endif
+  }
+
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
diff --git a/libstdc++-v3/config/io/basic_file_stdio.h b/libstdc++-v3/config/io/basic_file_stdio.h
index 29bd653..7b735654 100644
--- a/libstdc++-v3/config/io/basic_file_stdio.h
+++ b/libstdc++-v3/config/io/basic_file_stdio.h
@@ -127,6 +127,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       streamsize
       showmanyc();
+
+#if __cplusplus >= 201103L
+#ifdef _GLIBCXX_USE_STDIO_PURE
+      using native_handle_type = __c_file*; // FILE*
+#elif _GLIBCXX_USE__GET_OSFHANDLE
+      using native_handle_type = void*;     // HANDLE
+#else
+      using native_handle_type = int;       // POSIX file descriptor
+#endif
+
+      native_handle_type
+      native_handle() const noexcept;
+#endif
     };
 
 _GLIBCXX_END_NAMESPACE_VERSION