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>

1 files changed, 68 insertions, 2 deletions

diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index bef2b84..65ce679 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -5529,7 +5529,7 @@ $as_echo "$ac_cv_path_EGREP" >&6; }
   # expandable list at autoconf time; the second provides an expandable list
   # (i.e., shell variable) at configure time.
 
-  SUBDIRS='include libsupc++ src src/c++98 src/c++11 src/c++17 src/c++20 src/c++23 src/filesystem src/libbacktrace src/experimental doc po testsuite python'
+  SUBDIRS='include libsupc++ src src/c++98 src/c++11 src/c++17 src/c++20 src/c++23 src/c++26 src/filesystem src/libbacktrace src/experimental doc po testsuite python'
 
   # These need to be absolute paths, yet at the same time need to
   # canonicalize only relative paths, because then amd will not unmount
@@ -54517,6 +54517,60 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
+# For std::text_encoding
+
+
+  ac_ext=cpp
+ac_cpp='$CXXCPP $CPPFLAGS'
+ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
+
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether nl_langinfo_l is defined in <langinfo.h>" >&5
+$as_echo_n "checking whether nl_langinfo_l is defined in <langinfo.h>... " >&6; }
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+  #include <locale.h>
+  #include <langinfo.h>
+
+int
+main ()
+{
+
+    locale_t loc = newlocale(LC_ALL_MASK, "", (locale_t)0);
+    const char* enc = nl_langinfo_l(CODESET, loc);
+    freelocale(loc);
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  ac_nl_langinfo_l=yes
+else
+  ac_nl_langinfo_l=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_nl_langinfo_l" >&5
+$as_echo "$ac_nl_langinfo_l" >&6; }
+  if test "$ac_nl_langinfo_l" = yes; then
+
+cat >>confdefs.h <<_ACEOF
+#define _GLIBCXX_USE_NL_LANGINFO_L 1
+_ACEOF
+
+  fi
+
+  ac_ext=c
+ac_cpp='$CPP $CPPFLAGS'
+ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_c_compiler_gnu
+
+
+
 # Define documentation rules conditionally.
 
 # See if makeinfo has been installed and is modern enough
@@ -55637,7 +55691,7 @@ ac_config_files="$ac_config_files src/libbacktrace/backtrace-supported.h"
 # append it here.  Only modify Makefiles that have just been created.
 #
 # Also, get rid of this simulated-VPATH thing that automake does.
-ac_config_files="$ac_config_files include/Makefile libsupc++/Makefile src/Makefile src/c++98/Makefile src/c++11/Makefile src/c++17/Makefile src/c++20/Makefile src/c++23/Makefile src/filesystem/Makefile src/libbacktrace/Makefile src/experimental/Makefile doc/Makefile po/Makefile testsuite/Makefile python/Makefile"
+ac_config_files="$ac_config_files include/Makefile libsupc++/Makefile src/Makefile src/c++98/Makefile src/c++11/Makefile src/c++17/Makefile src/c++20/Makefile src/c++23/Makefile src/c++26/Makefile src/filesystem/Makefile src/libbacktrace/Makefile src/experimental/Makefile doc/Makefile po/Makefile testsuite/Makefile python/Makefile"
 
 
 ac_config_commands="$ac_config_commands generate-headers"
@@ -56893,6 +56947,7 @@ do
     "src/c++17/Makefile") CONFIG_FILES="$CONFIG_FILES src/c++17/Makefile" ;;
     "src/c++20/Makefile") CONFIG_FILES="$CONFIG_FILES src/c++20/Makefile" ;;
     "src/c++23/Makefile") CONFIG_FILES="$CONFIG_FILES src/c++23/Makefile" ;;
+    "src/c++26/Makefile") CONFIG_FILES="$CONFIG_FILES src/c++26/Makefile" ;;
     "src/filesystem/Makefile") CONFIG_FILES="$CONFIG_FILES src/filesystem/Makefile" ;;
     "src/libbacktrace/Makefile") CONFIG_FILES="$CONFIG_FILES src/libbacktrace/Makefile" ;;
     "src/experimental/Makefile") CONFIG_FILES="$CONFIG_FILES src/experimental/Makefile" ;;
@@ -58404,6 +58459,17 @@ _EOF
    . ${multi_basedir}/config-ml.in
    { ml_norecursion=; unset ml_norecursion;}
  ;;
+    "src/c++26/Makefile":F) cat > vpsed$$ << \_EOF
+s!`test -f '$<' || echo '$(srcdir)/'`!!
+_EOF
+   sed -f vpsed$$ $ac_file > tmp$$
+   mv tmp$$ $ac_file
+   rm vpsed$$
+   echo 'MULTISUBDIR =' >> $ac_file
+   ml_norecursion=yes
+   . ${multi_basedir}/config-ml.in
+   { ml_norecursion=; unset ml_norecursion;}
+ ;;
     "src/filesystem/Makefile":F) cat > vpsed$$ << \_EOF
 s!`test -f '$<' || echo '$(srcdir)/'`!!
 _EOF