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

This is another C++26 change, approved in Varna 2023. We require a new
static array of data that is extracted from the IANA Character Sets
database. A new Python script to generate a header from the IANA CSV
file is added.

The text_encoding class is basically just a pointer to an {ID,name} pair
in the static array. The aliases view is also just the same pointer (or
empty), and the view's iterator moves forwards and backwards in the
array while the array elements have the same ID (or to one element
further, for a past-the-end iterator).

Because those iterators refer to a global array that never goes out of
scope, there's no reason they should every produce undefined behaviour
or indeterminate values.  They should either have well-defined
behaviour, or abort. The overhead of ensuring those properties is pretty
low, so seems worth it.

This means that an aliases_view iterator should never be able to access
out-of-bounds. A non-value-initialized iterator always points to an
element of the static array even when not dereferenceable (the array has
unreachable entries at the start and end, which means that even a
past-the-end iterator for the last encoding in the array still points to
valid memory).  Dereferencing an iterator can always return a valid
array element, or "" for a non-dereferenceable iterator (but doing so
will abort when assertions are enabled).  In the language being proposed
for C++26, dereferencing an invalid iterator erroneously returns "".
Attempting to increment/decrement past the last/first element in the
view is erroneously a no-op, so aborts when assertions are enabled, and
doesn't change value otherwise.

Similarly, constructing a std::text_encoding with an invalid id (one
that doesn't have the value of an enumerator) erroneously behaves the
same as constructing with id::unknown, or aborts with assertions
enabled.

libstdc++-v3/ChangeLog:

	PR libstdc++/113318
	* acinclude.m4 (GLIBCXX_CONFIGURE): Add c++26 directory.
	(GLIBCXX_CHECK_TEXT_ENCODING): Define.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Use GLIBCXX_CHECK_TEXT_ENCODING.
	* include/Makefile.am: Add new headers.
	* include/Makefile.in: Regenerate.
	* include/bits/locale_classes.h (locale::encoding): Declare new
	member function.
	* include/bits/unicode.h (__charset_alias_match): New function.
	* include/bits/text_encoding-data.h: New file.
	* include/bits/version.def (text_encoding): Define.
	* include/bits/version.h: Regenerate.
	* include/std/text_encoding: New file.
	* src/Makefile.am: Add new subdirectory.
	* src/Makefile.in: Regenerate.
	* src/c++26/Makefile.am: New file.
	* src/c++26/Makefile.in: New file.
	* src/c++26/text_encoding.cc: New file.
	* src/experimental/Makefile.am: Include c++26 convenience
	library.
	* src/experimental/Makefile.in: Regenerate.
	* python/libstdcxx/v6/printers.py (StdTextEncodingPrinter): New
	printer.
	* scripts/gen_text_encoding_data.py: New file.
	* testsuite/22_locale/locale/encoding.cc: New test.
	* testsuite/ext/unicode/charset_alias_match.cc: New test.
	* testsuite/std/text_encoding/cons.cc: New test.
	* testsuite/std/text_encoding/members.cc: New test.
	* testsuite/std/text_encoding/requirements.cc: New test.

Reviewed-by: Ulrich Drepper <drepper.fsp@gmail.com>
Reviewed-by: Patrick Palka <ppalka@redhat.com>

7 files changed, 957 insertions, 4 deletions

diff --git a/libstdc++-v3/src/Makefile.am b/libstdc++-v3/src/Makefile.am
index 7292ae7..37ba149 100644
--- a/libstdc++-v3/src/Makefile.am
+++ b/libstdc++-v3/src/Makefile.am
@@ -43,7 +43,7 @@ experimental_dir =
 endif
 
 ## Keep this list sync'd with acinclude.m4:GLIBCXX_CONFIGURE.
-SUBDIRS = c++98 c++11 c++17 c++20 c++23 \
+SUBDIRS = c++98 c++11 c++17 c++20 c++23 c++26 \
 	$(filesystem_dir) $(backtrace_dir) $(experimental_dir)
 
 # Cross compiler support.
@@ -77,6 +77,7 @@ vpath % $(top_srcdir)/src/c++11
 vpath % $(top_srcdir)/src/c++17
 vpath % $(top_srcdir)/src/c++20
 vpath % $(top_srcdir)/src/c++23
+vpath % $(top_srcdir)/src/c++26
 if ENABLE_FILESYSTEM_TS
 vpath % $(top_srcdir)/src/filesystem
 endif
diff --git a/libstdc++-v3/src/Makefile.in b/libstdc++-v3/src/Makefile.in
index 31819c9..1bdf0da 100644
--- a/libstdc++-v3/src/Makefile.in
+++ b/libstdc++-v3/src/Makefile.in
@@ -241,8 +241,8 @@ am__define_uniq_tagged_files = \
   done | $(am__uniquify_input)`
 ETAGS = etags
 CTAGS = ctags
-DIST_SUBDIRS = c++98 c++11 c++17 c++20 c++23 filesystem libbacktrace \
-	experimental
+DIST_SUBDIRS = c++98 c++11 c++17 c++20 c++23 c++26 filesystem \
+	libbacktrace experimental
 ABI_TWEAKS_SRCDIR = @ABI_TWEAKS_SRCDIR@
 ACLOCAL = @ACLOCAL@
 ALLOCATOR_H = @ALLOCATOR_H@
@@ -491,7 +491,7 @@ AM_CPPFLAGS = $(GLIBCXX_INCLUDES) $(CPPFLAGS)
 @GLIBCXX_HOSTED_FALSE@backtrace_dir = 
 @GLIBCXX_HOSTED_FALSE@experimental_dir = 
 @GLIBCXX_HOSTED_TRUE@experimental_dir = experimental
-SUBDIRS = c++98 c++11 c++17 c++20 c++23 \
+SUBDIRS = c++98 c++11 c++17 c++20 c++23 c++26 \
 	$(filesystem_dir) $(backtrace_dir) $(experimental_dir)
 
 @VTV_CYGMIN_FALSE@toolexeclib_LTLIBRARIES = libstdc++.la
@@ -1024,6 +1024,7 @@ vpath % $(top_srcdir)/src/c++11
 vpath % $(top_srcdir)/src/c++17
 vpath % $(top_srcdir)/src/c++20
 vpath % $(top_srcdir)/src/c++23
+vpath % $(top_srcdir)/src/c++26
 @ENABLE_FILESYSTEM_TS_TRUE@vpath % $(top_srcdir)/src/filesystem
 @ENABLE_BACKTRACE_TRUE@vpath % $(top_srcdir)/src/libbacktrace
 vpath % $(top_srcdir)/src/experimental
diff --git a/libstdc++-v3/src/c++26/Makefile.am b/libstdc++-v3/src/c++26/Makefile.am
new file mode 100644
index 0000000..000ced1
--- /dev/null
+++ b/libstdc++-v3/src/c++26/Makefile.am
@@ -0,0 +1,109 @@
+## Makefile for the C++26 sources of the GNU C++ Standard library.
+##
+## Copyright (C) 1997-2023 Free Software Foundation, Inc.
+##
+## This file is part of the libstdc++ version 3 distribution.
+## Process this file with automake to produce Makefile.in.
+
+## This file is part of the GNU ISO C++ Library.  This library is free
+## software; you can redistribute it and/or modify it under the
+## terms of the GNU General Public License as published by the
+## Free Software Foundation; either version 3, or (at your option)
+## any later version.
+
+## This library is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+
+## You should have received a copy of the GNU General Public License along
+## with this library; see the file COPYING3.  If not see
+## <http://www.gnu.org/licenses/>.
+
+include $(top_srcdir)/fragment.am
+
+# Convenience library for C++26 runtime.
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+
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+
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+# XTEMPLATE_FLAGS = -fno-implicit-templates
+inst_sources =
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+
+sources = text_encoding.cc
+
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+
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new file mode 100644
index 0000000..77e73b2
--- /dev/null
+++ b/libstdc++-v3/src/c++26/Makefile.in
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+OS_INC_SRCDIR = @OS_INC_SRCDIR@
+OTOOL = @OTOOL@
+OTOOL64 = @OTOOL64@
+PACKAGE = @PACKAGE@
+PACKAGE_BUGREPORT = @PACKAGE_BUGREPORT@
+PACKAGE_NAME = @PACKAGE_NAME@
+PACKAGE_STRING = @PACKAGE_STRING@
+PACKAGE_TARNAME = @PACKAGE_TARNAME@
+PACKAGE_URL = @PACKAGE_URL@
+PACKAGE_VERSION = @PACKAGE_VERSION@
+PATH_SEPARATOR = @PATH_SEPARATOR@
+PDFLATEX = @PDFLATEX@
+RANLIB = @RANLIB@
+SECTION_FLAGS = @SECTION_FLAGS@
+SECTION_LDFLAGS = @SECTION_LDFLAGS@
+SED = @SED@
+SET_MAKE = @SET_MAKE@
+SHELL = @SHELL@
+STRIP = @STRIP@
+SYMVER_FILE = @SYMVER_FILE@
+TOPLEVEL_INCLUDES = @TOPLEVEL_INCLUDES@
+USE_NLS = @USE_NLS@
+VERSION = @VERSION@
+VIEW_FILE = @VIEW_FILE@
+VTV_CXXFLAGS = @VTV_CXXFLAGS@
+VTV_CXXLINKFLAGS = @VTV_CXXLINKFLAGS@
+VTV_PCH_CXXFLAGS = @VTV_PCH_CXXFLAGS@
+WARN_FLAGS = @WARN_FLAGS@
+XMLCATALOG = @XMLCATALOG@
+XMLLINT = @XMLLINT@
+XSLTPROC = @XSLTPROC@
+XSL_STYLE_DIR = @XSL_STYLE_DIR@
+abs_builddir = @abs_builddir@
+abs_srcdir = @abs_srcdir@
+abs_top_builddir = @abs_top_builddir@
+abs_top_srcdir = @abs_top_srcdir@
+ac_ct_CC = @ac_ct_CC@
+ac_ct_CXX = @ac_ct_CXX@
+ac_ct_DUMPBIN = @ac_ct_DUMPBIN@
+am__leading_dot = @am__leading_dot@
+am__tar = @am__tar@
+am__untar = @am__untar@
+baseline_dir = @baseline_dir@
+baseline_subdir_switch = @baseline_subdir_switch@
+bindir = @bindir@
+build = @build@
+build_alias = @build_alias@
+build_cpu = @build_cpu@
+build_os = @build_os@
+build_vendor = @build_vendor@
+builddir = @builddir@
+check_msgfmt = @check_msgfmt@
+datadir = @datadir@
+datarootdir = @datarootdir@
+docdir = @docdir@
+dvidir = @dvidir@
+enable_shared = @enable_shared@
+enable_static = @enable_static@
+exec_prefix = @exec_prefix@
+get_gcc_base_ver = @get_gcc_base_ver@
+glibcxx_MOFILES = @glibcxx_MOFILES@
+glibcxx_PCHFLAGS = @glibcxx_PCHFLAGS@
+glibcxx_POFILES = @glibcxx_POFILES@
+glibcxx_builddir = @glibcxx_builddir@
+glibcxx_compiler_pic_flag = @glibcxx_compiler_pic_flag@
+glibcxx_compiler_shared_flag = @glibcxx_compiler_shared_flag@
+glibcxx_cxx98_abi = @glibcxx_cxx98_abi@
+glibcxx_localedir = @glibcxx_localedir@
+glibcxx_lt_pic_flag = @glibcxx_lt_pic_flag@
+glibcxx_prefixdir = @glibcxx_prefixdir@
+glibcxx_srcdir = @glibcxx_srcdir@
+glibcxx_toolexecdir = @glibcxx_toolexecdir@
+glibcxx_toolexeclibdir = @glibcxx_toolexeclibdir@
+gxx_include_dir = @gxx_include_dir@
+host = @host@
+host_alias = @host_alias@
+host_cpu = @host_cpu@
+host_os = @host_os@
+host_vendor = @host_vendor@
+htmldir = @htmldir@
+includedir = @includedir@
+infodir = @infodir@
+install_sh = @install_sh@
+libdir = @libdir@
+libexecdir = @libexecdir@
+libtool_VERSION = @libtool_VERSION@
+localedir = @localedir@
+localstatedir = @localstatedir@
+lt_host_flags = @lt_host_flags@
+mandir = @mandir@
+mkdir_p = @mkdir_p@
+multi_basedir = @multi_basedir@
+oldincludedir = @oldincludedir@
+pdfdir = @pdfdir@
+port_specific_symbol_files = @port_specific_symbol_files@
+prefix = @prefix@
+program_transform_name = @program_transform_name@
+psdir = @psdir@
+python_mod_dir = @python_mod_dir@
+sbindir = @sbindir@
+sharedstatedir = @sharedstatedir@
+srcdir = @srcdir@
+sysconfdir = @sysconfdir@
+target = @target@
+target_alias = @target_alias@
+target_cpu = @target_cpu@
+target_os = @target_os@
+target_vendor = @target_vendor@
+thread_header = @thread_header@
+tmake_file = @tmake_file@
+top_build_prefix = @top_build_prefix@
+top_builddir = @top_builddir@
+top_srcdir = @top_srcdir@
+toplevel_builddir = @toplevel_builddir@
+toplevel_srcdir = @toplevel_srcdir@
+
+# May be used by various substitution variables.
+gcc_version := $(shell @get_gcc_base_ver@ $(top_srcdir)/../gcc/BASE-VER)
+MAINT_CHARSET = latin1
+mkinstalldirs = $(SHELL) $(toplevel_srcdir)/mkinstalldirs
+PWD_COMMAND = $${PWDCMD-pwd}
+STAMP = echo timestamp >
+toolexecdir = $(glibcxx_toolexecdir)
+toolexeclibdir = $(glibcxx_toolexeclibdir)
+@ENABLE_WERROR_FALSE@WERROR_FLAG = 
+@ENABLE_WERROR_TRUE@WERROR_FLAG = -Werror
+@ENABLE_EXTERN_TEMPLATE_FALSE@XTEMPLATE_FLAGS = 
+@ENABLE_EXTERN_TEMPLATE_TRUE@XTEMPLATE_FLAGS = -fno-implicit-templates
+@GLIBCXX_LDBL_ALT128_COMPAT_FALSE@LDBL_128_FLAGS = 
+@GLIBCXX_LDBL_ALT128_COMPAT_TRUE@LDBL_128_FLAGS = $(LONG_DOUBLE_128_FLAGS)
+
+# These bits are all figured out from configure.  Look in acinclude.m4
+# or configure.ac to see how they are set.  See GLIBCXX_EXPORT_FLAGS.
+CONFIG_CXXFLAGS = \
+	$(SECTION_FLAGS) $(HWCAP_CFLAGS) -frandom-seed=$@ $(LDBL_128_FLAGS)
+
+WARN_CXXFLAGS = \
+	$(WARN_FLAGS) $(WERROR_FLAG) -fdiagnostics-show-location=once 
+
+
+# -I/-D flags to pass when compiling.
+AM_CPPFLAGS = $(GLIBCXX_INCLUDES) $(CPPFLAGS)
+
+# Convenience library for C++26 runtime.
+noinst_LTLIBRARIES = libc++26convenience.la
+headers = 
+# XTEMPLATE_FLAGS =
+@ENABLE_EXTERN_TEMPLATE_FALSE@inst_sources = 
+
+# XTEMPLATE_FLAGS = -fno-implicit-templates
+@ENABLE_EXTERN_TEMPLATE_TRUE@inst_sources = 
+sources = text_encoding.cc
+@GLIBCXX_HOSTED_FALSE@libc__26convenience_la_SOURCES = 
+@GLIBCXX_HOSTED_TRUE@libc__26convenience_la_SOURCES = $(sources)  $(inst_sources)
+
+# AM_CXXFLAGS needs to be in each subdirectory so that it can be
+# modified in a per-library or per-sub-library way.  Need to manually
+# set this option because CONFIG_CXXFLAGS has to be after
+# OPTIMIZE_CXXFLAGS on the compile line so that -O2 can be overridden
+# as the occasion calls for it.
+AM_CXXFLAGS = \
+	-std=gnu++26 \
+	$(glibcxx_lt_pic_flag) $(glibcxx_compiler_shared_flag) \
+	$(XTEMPLATE_FLAGS) $(VTV_CXXFLAGS) \
+	$(WARN_CXXFLAGS) $(OPTIMIZE_CXXFLAGS) $(CONFIG_CXXFLAGS) \
+	-fimplicit-templates
+
+AM_MAKEFLAGS = \
+	"gxx_include_dir=$(gxx_include_dir)"
+
+
+# Libtool notes
+
+# 1) In general, libtool expects an argument such as `--tag=CXX' when
+# using the C++ compiler, because that will enable the settings
+# detected when C++ support was being configured.  However, when no
+# such flag is given in the command line, libtool attempts to figure
+# it out by matching the compiler name in each configuration section
+# against a prefix of the command line.  The problem is that, if the
+# compiler name and its initial flags stored in the libtool
+# configuration file don't match those in the command line, libtool
+# can't decide which configuration to use, and it gives up.  The
+# correct solution is to add `--tag CXX' to LTCXXCOMPILE and maybe
+# CXXLINK, just after $(LIBTOOL), so that libtool doesn't have to
+# attempt to infer which configuration to use.
+#
+# The second tag argument, `--tag disable-shared` means that libtool
+# only compiles each source once, for static objects. In actuality,
+# glibcxx_lt_pic_flag and glibcxx_compiler_shared_flag are added to
+# the libtool command that is used create the object, which is
+# suitable for shared libraries.  The `--tag disable-shared` must be
+# placed after --tag CXX lest things CXX undo the affect of
+# disable-shared.
+
+# 2) Need to explicitly set LTCXXCOMPILE so that EXTRA_CXX_FLAGS is
+# last. (That way, things like -O2 passed down from the toplevel can
+# be overridden by --enable-debug.)
+LTCXXCOMPILE = \
+	$(LIBTOOL) --tag CXX --tag disable-shared \
+	$(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
+	--mode=compile $(CXX) $(TOPLEVEL_INCLUDES) \
+	$(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CXXFLAGS) $(CXXFLAGS) $(EXTRA_CXX_FLAGS)
+
+LTLDFLAGS = $(shell $(SHELL) $(top_srcdir)/../libtool-ldflags $(LDFLAGS))
+
+# 3) We'd have a problem when building the shared libstdc++ object if
+# the rules automake generates would be used.  We cannot allow g++ to
+# be used since this would add -lstdc++ to the link line which of
+# course is problematic at this point.  So, we get the top-level
+# directory to configure libstdc++-v3 to use gcc as the C++
+# compilation driver.
+CXXLINK = \
+	$(LIBTOOL) --tag CXX --tag disable-shared \
+	$(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
+	--mode=link $(CXX) \
+	$(VTV_CXXLINKFLAGS) \
+	$(OPT_LDFLAGS) $(SECTION_LDFLAGS) $(AM_CXXFLAGS) $(LTLDFLAGS) -o $@
+
+all: all-am
+
+.SUFFIXES:
+.SUFFIXES: .cc .lo .o .obj
+$(srcdir)/Makefile.in: @MAINTAINER_MODE_TRUE@ $(srcdir)/Makefile.am $(top_srcdir)/fragment.am $(am__configure_deps)
+	@for dep in $?; do \
+	  case '$(am__configure_deps)' in \
+	    *$$dep*) \
+	      ( cd $(top_builddir) && $(MAKE) $(AM_MAKEFLAGS) am--refresh ) \
+	        && { if test -f $@; then exit 0; else break; fi; }; \
+	      exit 1;; \
+	  esac; \
+	done; \
+	echo ' cd $(top_srcdir) && $(AUTOMAKE) --foreign --ignore-deps src/c++26/Makefile'; \
+	$(am__cd) $(top_srcdir) && \
+	  $(AUTOMAKE) --foreign --ignore-deps src/c++26/Makefile
+Makefile: $(srcdir)/Makefile.in $(top_builddir)/config.status
+	@case '$?' in \
+	  *config.status*) \
+	    cd $(top_builddir) && $(MAKE) $(AM_MAKEFLAGS) am--refresh;; \
+	  *) \
+	    echo ' cd $(top_builddir) && $(SHELL) ./config.status $(subdir)/$@ $(am__depfiles_maybe)'; \
+	    cd $(top_builddir) && $(SHELL) ./config.status $(subdir)/$@ $(am__depfiles_maybe);; \
+	esac;
+$(top_srcdir)/fragment.am $(am__empty):
+
+$(top_builddir)/config.status: $(top_srcdir)/configure $(CONFIG_STATUS_DEPENDENCIES)
+	cd $(top_builddir) && $(MAKE) $(AM_MAKEFLAGS) am--refresh
+
+$(top_srcdir)/configure: @MAINTAINER_MODE_TRUE@ $(am__configure_deps)
+	cd $(top_builddir) && $(MAKE) $(AM_MAKEFLAGS) am--refresh
+$(ACLOCAL_M4): @MAINTAINER_MODE_TRUE@ $(am__aclocal_m4_deps)
+	cd $(top_builddir) && $(MAKE) $(AM_MAKEFLAGS) am--refresh
+$(am__aclocal_m4_deps):
+
+clean-noinstLTLIBRARIES:
+	-test -z "$(noinst_LTLIBRARIES)" || rm -f $(noinst_LTLIBRARIES)
+	@list='$(noinst_LTLIBRARIES)'; \
+	locs=`for p in $$list; do echo $$p; done | \
+	      sed 's|^[^/]*$$|.|; s|/[^/]*$$||; s|$$|/so_locations|' | \
+	      sort -u`; \
+	test -z "$$locs" || { \
+	  echo rm -f $${locs}; \
+	  rm -f $${locs}; \
+	}
+
+libc++26convenience.la: $(libc__26convenience_la_OBJECTS) $(libc__26convenience_la_DEPENDENCIES) $(EXTRA_libc__26convenience_la_DEPENDENCIES) 
+	$(AM_V_CXXLD)$(CXXLINK)  $(libc__26convenience_la_OBJECTS) $(libc__26convenience_la_LIBADD) $(LIBS)
+
+mostlyclean-compile:
+	-rm -f *.$(OBJEXT)
+
+distclean-compile:
+	-rm -f *.tab.c
+
+.cc.o:
+	$(AM_V_CXX)$(CXXCOMPILE) -c -o $@ $<
+
+.cc.obj:
+	$(AM_V_CXX)$(CXXCOMPILE) -c -o $@ `$(CYGPATH_W) '$<'`
+
+.cc.lo:
+	$(AM_V_CXX)$(LTCXXCOMPILE) -c -o $@ $<
+
+mostlyclean-libtool:
+	-rm -f *.lo
+
+clean-libtool:
+	-rm -rf .libs _libs
+
+ID: $(am__tagged_files)
+	$(am__define_uniq_tagged_files); mkid -fID $$unique
+tags: tags-am
+TAGS: tags
+
+tags-am: $(TAGS_DEPENDENCIES) $(am__tagged_files)
+	set x; \
+	here=`pwd`; \
+	$(am__define_uniq_tagged_files); \
+	shift; \
+	if test -z "$(ETAGS_ARGS)$$*$$unique"; then :; else \
+	  test -n "$$unique" || unique=$$empty_fix; \
+	  if test $$# -gt 0; then \
+	    $(ETAGS) $(ETAGSFLAGS) $(AM_ETAGSFLAGS) $(ETAGS_ARGS) \
+	      "$$@" $$unique; \
+	  else \
+	    $(ETAGS) $(ETAGSFLAGS) $(AM_ETAGSFLAGS) $(ETAGS_ARGS) \
+	      $$unique; \
+	  fi; \
+	fi
+ctags: ctags-am
+
+CTAGS: ctags
+ctags-am: $(TAGS_DEPENDENCIES) $(am__tagged_files)
+	$(am__define_uniq_tagged_files); \
+	test -z "$(CTAGS_ARGS)$$unique" \
+	  || $(CTAGS) $(CTAGSFLAGS) $(AM_CTAGSFLAGS) $(CTAGS_ARGS) \
+	     $$unique
+
+GTAGS:
+	here=`$(am__cd) $(top_builddir) && pwd` \
+	  && $(am__cd) $(top_srcdir) \
+	  && gtags -i $(GTAGS_ARGS) "$$here"
+cscopelist: cscopelist-am
+
+cscopelist-am: $(am__tagged_files)
+	list='$(am__tagged_files)'; \
+	case "$(srcdir)" in \
+	  [\\/]* | ?:[\\/]*) sdir="$(srcdir)" ;; \
+	  *) sdir=$(subdir)/$(srcdir) ;; \
+	esac; \
+	for i in $$list; do \
+	  if test -f "$$i"; then \
+	    echo "$(subdir)/$$i"; \
+	  else \
+	    echo "$$sdir/$$i"; \
+	  fi; \
+	done >> $(top_builddir)/cscope.files
+
+distclean-tags:
+	-rm -f TAGS ID GTAGS GRTAGS GSYMS GPATH tags
+check-am: all-am
+check: check-am
+all-am: Makefile $(LTLIBRARIES)
+installdirs:
+install: install-am
+install-exec: install-exec-am
+install-data: install-data-am
+uninstall: uninstall-am
+
+install-am: all-am
+	@$(MAKE) $(AM_MAKEFLAGS) install-exec-am install-data-am
+
+installcheck: installcheck-am
+install-strip:
+	if test -z '$(STRIP)'; then \
+	  $(MAKE) $(AM_MAKEFLAGS) INSTALL_PROGRAM="$(INSTALL_STRIP_PROGRAM)" \
+	    install_sh_PROGRAM="$(INSTALL_STRIP_PROGRAM)" INSTALL_STRIP_FLAG=-s \
+	      install; \
+	else \
+	  $(MAKE) $(AM_MAKEFLAGS) INSTALL_PROGRAM="$(INSTALL_STRIP_PROGRAM)" \
+	    install_sh_PROGRAM="$(INSTALL_STRIP_PROGRAM)" INSTALL_STRIP_FLAG=-s \
+	    "INSTALL_PROGRAM_ENV=STRIPPROG='$(STRIP)'" install; \
+	fi
+mostlyclean-generic:
+
+clean-generic:
+
+distclean-generic:
+	-test -z "$(CONFIG_CLEAN_FILES)" || rm -f $(CONFIG_CLEAN_FILES)
+	-test . = "$(srcdir)" || test -z "$(CONFIG_CLEAN_VPATH_FILES)" || rm -f $(CONFIG_CLEAN_VPATH_FILES)
+
+maintainer-clean-generic:
+	@echo "This command is intended for maintainers to use"
+	@echo "it deletes files that may require special tools to rebuild."
+clean: clean-am
+
+clean-am: clean-generic clean-libtool clean-noinstLTLIBRARIES \
+	mostlyclean-am
+
+distclean: distclean-am
+	-rm -f Makefile
+distclean-am: clean-am distclean-compile distclean-generic \
+	distclean-tags
+
+dvi: dvi-am
+
+dvi-am:
+
+html: html-am
+
+html-am:
+
+info: info-am
+
+info-am:
+
+install-data-am:
+
+install-dvi: install-dvi-am
+
+install-dvi-am:
+
+install-exec-am:
+
+install-html: install-html-am
+
+install-html-am:
+
+install-info: install-info-am
+
+install-info-am:
+
+install-man:
+
+install-pdf: install-pdf-am
+
+install-pdf-am:
+
+install-ps: install-ps-am
+
+install-ps-am:
+
+installcheck-am:
+
+maintainer-clean: maintainer-clean-am
+	-rm -f Makefile
+maintainer-clean-am: distclean-am maintainer-clean-generic
+
+mostlyclean: mostlyclean-am
+
+mostlyclean-am: mostlyclean-compile mostlyclean-generic \
+	mostlyclean-libtool
+
+pdf: pdf-am
+
+pdf-am:
+
+ps: ps-am
+
+ps-am:
+
+uninstall-am:
+
+.MAKE: install-am install-strip
+
+.PHONY: CTAGS GTAGS TAGS all all-am check check-am clean clean-generic \
+	clean-libtool clean-noinstLTLIBRARIES cscopelist-am ctags \
+	ctags-am distclean distclean-compile distclean-generic \
+	distclean-libtool distclean-tags dvi dvi-am html html-am info \
+	info-am install install-am install-data install-data-am \
+	install-dvi install-dvi-am install-exec install-exec-am \
+	install-html install-html-am install-info install-info-am \
+	install-man install-pdf install-pdf-am install-ps \
+	install-ps-am install-strip installcheck installcheck-am \
+	installdirs maintainer-clean maintainer-clean-generic \
+	mostlyclean mostlyclean-compile mostlyclean-generic \
+	mostlyclean-libtool pdf pdf-am ps ps-am tags tags-am uninstall \
+	uninstall-am
+
+.PRECIOUS: Makefile
+
+
+vpath % $(top_srcdir)/src/c++26
+
+# Tell versions [3.59,3.63) of GNU make to not export all variables.
+# Otherwise a system limit (for SysV at least) may be exceeded.
+.NOEXPORT:
diff --git a/libstdc++-v3/src/c++26/text_encoding.cc b/libstdc++-v3/src/c++26/text_encoding.cc
new file mode 100644
index 0000000..33c6c07
--- /dev/null
+++ b/libstdc++-v3/src/c++26/text_encoding.cc
@@ -0,0 +1,91 @@
+// Definitions for <text_encoding> -*- C++ -*-
+
+// Copyright The GNU Toolchain Authors.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+#include <text_encoding>
+#include <locale>
+
+#ifdef _GLIBCXX_USE_NL_LANGINFO_L
+#include <locale.h>
+#include <langinfo.h>
+
+#if __CHAR_BIT__ == 8
+namespace std
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+text_encoding
+__locale_encoding(const char* name)
+{
+  text_encoding enc;
+  if (locale_t loc = ::newlocale(LC_CTYPE_MASK, name, (locale_t)0))
+    {
+      if (const char* codeset = ::nl_langinfo_l(CODESET, loc))
+	{
+	  string_view s(codeset);
+	  if (s.size() < text_encoding::max_name_length)
+	    enc = text_encoding(s);
+	}
+      ::freelocale(loc);
+    }
+  return enc;
+}
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+
+std::text_encoding
+std::text_encoding::environment()
+{
+  return std::__locale_encoding("");
+}
+
+bool
+std::text_encoding::_M_is_environment() const
+{
+  bool matched = false;
+  if (locale_t loc = ::newlocale(LC_CTYPE_MASK, "", (locale_t)0))
+    {
+      if (const char* codeset = ::nl_langinfo_l(CODESET, loc))
+	{
+	  string_view sv(codeset);
+	  for (auto alias : aliases())
+	    if (__unicode::__charset_alias_match(alias, sv))
+	      {
+		matched = true;
+		break;
+	      }
+	}
+      ::freelocale(loc);
+    }
+  return matched;
+}
+
+std::text_encoding
+std::locale::encoding() const
+{
+  return std::__locale_encoding(name().c_str());
+}
+#endif // CHAR_BIT == 8
+
+#endif // _GLIBCXX_USE_NL_LANGINFO_L
diff --git a/libstdc++-v3/src/experimental/Makefile.am b/libstdc++-v3/src/experimental/Makefile.am
index 8259f98..6241430 100644
--- a/libstdc++-v3/src/experimental/Makefile.am
+++ b/libstdc++-v3/src/experimental/Makefile.am
@@ -47,10 +47,12 @@ libstdc__exp_la_SOURCES = $(sources)
 
 libstdc__exp_la_LIBADD = \
 	$(top_builddir)/src/c++23/libc++23convenience.la \
+	$(top_builddir)/src/c++26/libc++26convenience.la \
 	$(filesystem_lib) $(backtrace_lib)
 
 libstdc__exp_la_DEPENDENCIES = \
 	$(top_builddir)/src/c++23/libc++23convenience.la \
+	$(top_builddir)/src/c++26/libc++26convenience.la \
 	$(filesystem_lib) $(backtrace_lib)
 
 # AM_CXXFLAGS needs to be in each subdirectory so that it can be
diff --git a/libstdc++-v3/src/experimental/Makefile.in b/libstdc++-v3/src/experimental/Makefile.in
index 0ff402d..13a1f2a 100644
--- a/libstdc++-v3/src/experimental/Makefile.in
+++ b/libstdc++-v3/src/experimental/Makefile.in
@@ -462,10 +462,12 @@ sources = \
 libstdc__exp_la_SOURCES = $(sources)
 libstdc__exp_la_LIBADD = \
 	$(top_builddir)/src/c++23/libc++23convenience.la \
+	$(top_builddir)/src/c++26/libc++26convenience.la \
 	$(filesystem_lib) $(backtrace_lib)
 
 libstdc__exp_la_DEPENDENCIES = \
 	$(top_builddir)/src/c++23/libc++23convenience.la \
+	$(top_builddir)/src/c++26/libc++26convenience.la \
 	$(filesystem_lib) $(backtrace_lib)