There is currently no `dllimport` attribute on any of our function,
which prevents MSVC to optimize function calls.
To fix that issue, we need to redeclare all our visibility macros for
each of our libraries, because when compiling e.g. GIO code, we need
dllimport in GLIB headers and dllexport in GIO headers. That means they
cannot use the same GLIB_AVAILABLE_* macro.
Since that's a lot of boilerplate to copy/paste after each version bump,
this MR generate all those macros using a python script.
Also simplify the meson side by using `gnu_symbol_visibility : 'hidden'`
keyword argument instead of passing the cflag manually.
This leaves only API index to add manually into glib-docs.xml when
bumping GLib version. That file cannot be generated because Meson does
not allow passing a buit file to gnome.gtkdoc()'s main_xml kwarg
unfortunately.
We require C99 now, and this warning was added for strict adherence to
C89 because GCC allowed mixed declarations in gnu89 as a GCC
extension. Let's get rid of this.
Commit 4a4d9eb662 initially switched Meson to find the python
program using find_program('python3'). Sadly that caused a
regression, since in some cases with MSVC it would fallback to
'meson.exe runpython', which is undesired.
However, that particular code was reverted back to an also
undesired lookup method, find_installation('python3'). This
way of finding python also breaks on Windows + MSVC, in particular
when setting it up as follows:
```
winget install python
winget install meson
```
This fails building GLib with:
> python3 not found
Fix that by not passing any argument to find_installation(), which
lets Meson figure it all out by itself.
The tests that functionally rely on G_ENABLE_DIAGNOSTIC=1 still set it
explicitly, so that they will behave as expected when run as
installed-tests or manually.
Signed-off-by: Simon McVittie <smcv@collabora.com>
We've various macros definitions that are depending using C++ features
that may not work in all the standard versions, so recompile the cxx
tests that we have in all the ones we want to support.
glib_debug is an auto option. This is clever because it allows us to
guess the best default based on the build type, while also allowing an
easy way to override if the guess is not good. Sadly, the attempt to
guess based on the build type does not work well. For example, it
considers debugoptimized builds to be debug builds, but despite the
name, it is definitely a release build type (except on Windows, which
we'll ignore here). The minsize build type has the exact same problem.
The debug option is true for both build types, but this only controls
whether debuginfo is enabled, not whether debug extras are enabled.
The plain build type has a different problem: debug is off, but the
optimization option is off too, even though plain builds are distro
builds are will almost always use optimization.
I've outlined an argument for why we should make these changes here:
https://blogs.gnome.org/mcatanzaro/2022/07/15/best-practices-for-build-options/
Specifically, Rule 4 shows all the build types and whether they
correspond to release builds or debug builds. Rule 6 argues that we
should provide good defaults for plain builds.
This is an internal helper executable, which users shouldn't invoke
directly (see glib#1633).
When building for a single-architecture distribution, we can install
it as ${libexecdir}/gio-launch-desktop.
When building for a multiarch distribution, installing it into an
architecture-specific location and packaging it alongside the GLib
library avoids the problem discussed in glib#1633 where it would either
cause a circular dependency between the GLib library and a common
cross-architecture package (libglib2.0-bin in Debian), or require a
separate package just to contain gio-launch-desktop, or cause different
architectures' copies to overwrite each other.
Signed-off-by: Simon McVittie <smcv@collabora.com>
In Debian-style multiarch (libdir = lib/x86_64-linux-gnu or similar),
Red-Hat-style multilib (libdir = lib64 or lib) and Arch-style multilib
(libdir = lib or lib32), we have to run a separate version of
gio-querymodules to discover 32- or 64-bit modules on x86. Installing
modules in the directory used for each word size needs to trigger
recompilation of the correct modules list.
Debian, Fedora and Arch currently all have patches to facilitate this:
Debian moves gio-querymodules into ${libdir}/glib-2.0 and provides a
compat symlink in ${bindir}, while Fedora and Arch rename one or both
of the gio-querymodules executables to give it a -32 or -64 suffix.
We can avoid the need for these patches by making this a build option.
Doing this upstream has the advantage that the pkg-config metadata for
each architecture points to the correct executable and is in sync with
reality.
I'm using Debian's installation scheme with a separate directory here,
because the word-size suffix used in Fedora and Arch only works for the
common case of 32- and 64-bit multilib, and does not cover scenarios
where there can be more than one ABI with the same word size, such as
multiarch cross-compilation or alternative ABIs like x32.
Now that we have this infrastructure, it's also convenient to use it for
glib-compile-schemas. This works with /usr/share, so it only needs to
be run for one architecture (typically the system's primary
architecture), but using /usr/bin/glib-compile-schemas for the trigger
would result in either primary and secondary architectures trying to
overwrite each other's /usr/bin/glib-compile-schemas binaries, or a
circular dependency (the GLib library would have to depend on a
common package that contains glib-compile-schemas, but
glib-compile-schemas depends on the GLib library). Installing a
glib-compile-schemas binary in an architecture-specific location
alongside each GLib library bypasses this problem.
Signed-off-by: Simon McVittie <smcv@collabora.com>
We don't need a cpp toolchain for building glib so lets just
automatically disable tests requiring one when not available.
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
This can catch the wrong pointer being passed to a function argument (in
some cases), with few false positives.
Spotted while testing !2529.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
When the system supports it (as all Linux kernels ≥ 5.3 should), it’s
preferable to use `pidfd_open()` and `waitid()` to be notified of
child processes exiting or being signalled, rather than installing a
default `SIGCHLD` handler.
A default `SIGCHLD` handler is global, and can never interact well with
other code (from the application or other libraries) which also wants to
install a `SIGCHLD` handler.
This use of `pidfd_open()` is racy (the PID may be reused between
`g_child_watch_source_new()` being called and `pidfd_open()` being
called), so it doesn’t improve behaviour there. For that, we’d need
continuous use of pidfds throughout GLib, from fork/spawn time until
here. See #1866 for that.
The use of `waitid()` to get the process exit status could be expanded
in future to also work for stopped or continued processes (as per #175)
by adding `WSTOPPED | WCONTINUED` into the flags. That’s a behaviour
change which is outside the strict scope of adding pidfd support,
though.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: #1866Fixes: #2216
We have fallback in places for GNU's variadic arguments in macros, and
for static inline functions with variadic arguments as an fallback of
last resort, but going forward we are going to depend on `__VA_ARGS__`
for macros that cannot be re-implemented using a static inline function.
Fixes: #2681
This means we can specify the standard options for testing GLib under
valgrind consistently, so that developers can use `meson test
--setup=valgrind` to run them.
Port the existing valgrind CI to use them (this will not change its
functional behaviour).
Suggested by Marco Trevisan at
https://gitlab.gnome.org/GNOME/glib/-/merge_requests/2717#note_1478891.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
intl is complicated to look up. Some of that complexity now resides in
Meson, since 0.59.0, via a `dependency('intl')` lookup, so use that
instead.
The Meson lookup doesn't include all the checks here, but likewise this
meson.build doesn't include all the checks in Meson. Particularly, the
following are different:
- Meson accurately detects support built into libc, even if that
conflicts with an external library version (which should be detected as
broken and thus not-found, but glib does not do so).
The problem here is that depending on which libintl.h header is first
in the search path, the *gettext symbols may be the libc ABI, or they
may be renamed to libintl_*gettext, then additionally take over the
*gettext names via a macro, in order to invoke the external library
version even on systems where there is a libc builtin. This means that
checking for `cc.has_function()` correctly reports that there is such
a function in libc, but that unfortunately does not mean it is usable,
because source code referencing `ngettext` etc. will expect to be
linked to `libintl_ngettext`.
- glib checks whether the found intl requires pthread, rather than
simply trusting the result of `cc.find_library()` for the external
library case.
Do the heavy lifting by using Meson to check for intl, and select the
correct implementation, but do a post-discovery check if the symbol is
linkable both with/without pthread.
The logic is still a bit hairy, and eventually more of the logic could
be moved into Meson. But it's better than before.
Fixes incorrect detection of intl on musl-based systems (which have a
less capable libc intl), when GNU libintl is installed as an external
library.
iconv is complicated to look up. That complexity now resides in
Meson, since 0.60.0, via a `dependency('iconv')` lookup, so use that
instead.
No effort is made to support the old option for which type of iconv to
use. It was a false choice, because if only one was available, then
that's the only one you can use, and if both are available, the external
iconv shadows the builtin one and renders the builtin one unusable,
so there is still only one you can use.
This meant that when configuring glib with -Diconv=libc on systems that
had an external iconv, the configure check would detect a valid libc
iconv, try to use it, and then fail during the build because iconv.h
belongs to the external iconv and generates machine code using the
external iconv ABI, but fails to link to the iconv `find_library()`.
Meson handles this transparently.
Rather than carrying the copylib around inside GLib, which is a pain to
synchronise and affects our code coverage statistics.
This requires updating the CI images to cache the new subproject,
including updating the `cache-subprojects.sh` script to pull in git
submodules.
It also requires adding `gioenumtypes_dep` to be added to the
dependencies list of `libgio`, since it needs to be build before GVDB as
it’s pulled in by the GIO headers which GVDB includes.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: #2603
Atomic APIs provide a way to exchange values only if we compare a value
that is equal to the old value, but not to just exchange the value
returning the old one.
However, compilers provide such built-in functions, so we can use them
to expose such functionality to GLib.
The only drawback is that when using an old version of gcc not providing
atomic APIs to swap values, we need to re-implement it with an
implementation that may not be fully atomic, but that is safe enough.
However this codepath should really not be used currently as gcc
introduced __atomic_exchange_n() at version 4.7.4, so 8 years ago.
Since Meson 0.54.0, `dependency('zlib')` will fallback on systems
without a pkg-config dependency, to a system dependency lookup that
performs the necessary `find_libary('z')` (or MSVC zlib/zlib1) and
`has_header('zlib.h')` checks.
This means all the manual lookups are no longer needed, and a single
dependency lookup covers all cases, and also clarifies the log lookup by
not sometimes listing "not found" a couple times.
With Meson 0.60 (or possibly some earlier versions) we can factor the
checks out as a variable can now be used as an array key. This
simplifies the checks a little, while introducing no functional
differences.
The contents of `g_sizet_compatibility` after this block are identical
with and without the changes applied.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Since Meson 0.47, this can be used to check a header with compilation,
rather than just stat. This removes a workaround.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Check the spawn implementation behaviour when the stderr is a
socket (mostly for win32).
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
As per meson spec, returncode() produces unspecified data if
compiled() == false. Check compiled() first to avoid relying
upon unspecified data.
In addition, muon -- an implemetation of meson written in C goes
further and forbids returning unspecified data. This is a good
decision, but also makes it harder to support applications which
wrongly use meson API. Therefore, application needs to be fixed.
It is not only shorter than `not meson.is_cross_build() or
meson.has_exe_wrapper()` but also handle the case of cross compiling to
a compatible arch such as building for i386 on an amd64.
Move msvc warnings in meson.build file from line 24 to line 469 to group
them next to gcc/clang warnings. So it is easier to see warnings flags
for all platforms at once.
This reverts commit 4a4d9eb662.
It seems to cause build failures with `VsDevCmd.bat` 2022:
```
..\meson.build:2274:0: ERROR: Command "C:\Program Files\Meson\meson.exe runpython --version" failed with status 2.
```
Revert it for now until this can be fixed in Meson.
See https://gitlab.gnome.org/GNOME/glib/-/merge_requests/2541#note_1410521
It can be treated like any other command, we don't need a full blown
module capable of building extensions just to get an ExternalProgram
executable that can be used to run scripts.
Since find_program has a builtin kwarg for requiring a given version, we
can avoid manually coding some checks and emitting a custom error.
When working with storage (especially GInputStream or GOutputStream) it
is preferred to use page-aligned buffers so that the operating system
can do page-mapping tricks as the operation passes through the kernel.
Another use case is allocating memory used for vectorised operations,
which must be aligned to specific boundaries.
POSIX and Windows, as well as the C11 specification, provide this kind
of allocator functions, and GLib already makes use of it inside GSlice.
It would be convenient to have a public, portable wrapper that other
projects can use.
Fixes: #2574
Glib cannot be built statically on Windows because glib, gobject and gio
modules need to perform specific initialization when DLL are loaded and
cleanup when unloaded. Those initializations and cleanups are performed
using the DllMain function which is not called with static builds.
Issue is known for a while and solutions were already proposed but never
merged (see: https://gitlab.gnome.org/GNOME/glib/-/issues/692). Last
patch is from version 2.36.x and since then the
"constructor/destructor" mechanism has been implemented and used in
other part of the system.
This patch takes back the old idea and updates it to the last version of
glib to allow static compilation on Windows.
WARNING: because DllMain doesn't exist anymore in static compilation
mode, there is no easy way of knowing when a Windows thread finishes.
This patch implements a workaround for glib threads created by calling
g_thread_new(), so all glib threads created through glib API will behave
exactly the same way in static and dynamic compilation modes.
Unfortunately, Windows threads created by using CreateThread() or
_beginthread/ex() will not work with glib TLS functions. If users need
absolutely to use a thread NOT created with glib API under Windows and
in static compilation mode, they should not use glib functions within
their thread or they may encounter memory leaks when the thread finishes.
This should not be an issue as users should use exclusively the glib API
to manipulate threads in order to be cross-platform compatible and this
would be very unlikely and cumbersome that they may mix up Windows native
threads API with glib one.
Closes#692
This code was skipping fsync on BTRFS because of an old guarantee about
the overwrite-by-rename behavior that no longer holds true. This has
been confirmed by the BTRFS developers to no longer be guaranteed since
Kernel 3.17 (August 2014), but it was guaranteed when this optimization
was first introduced in 2010.
This could result in empty files after crashes in applications using
g_file_set_contents(). Most prominently this might have been the cause
of dconf settings getting lost on BTRFS after crashes due to the
frequency with which such writes can happen in dconf.
See: https://gitlab.gnome.org/GNOME/dconf/-/issues/73
Using ld_flags would work, but that does not propagate ldflags to users
of glib. Meson's dependency() call will propagate apple framework
dependencies to downstream users.
Previously they were only passed to the C compiler, which meant disabled
warnings were still emitted when (for example) including C headers from
C++ and ObjC files.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
It is exactly the same wrap as the one in WrapDB but with a different
name. That fix error when multiple projects uses pcre and they don't
have the same wrap name:
meson.build:1:0: ERROR: Multiple wrap files provide 'libpcre' dependency: pcre.wrap and libpcre.wrap
This is what’s available in the new Debian Stable, so we can expect it
to be available pretty much everywhere.
Subsequent commits will clean up old workarounds.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Include the correct system headers for each test that meson performs.
This allows system capabilities to be detected correctly even if
implicit declaration of functions is considered an error.
This should maintain equivalent functionality, apart from that now you
have to pass `--force-fallback-for libpcre` to `meson configure` in
order to use the subproject; rather than specifying
`-Dinternal_pcre=true` to use the internal copy.
This also fixes#642, as the wrapdb copy of libpcre is version 8.37.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: #962Fixes: #642
If libintl is built statically on macOS, linking it requires passing
"-framework CoreFoundation" to satisfy symbol dependencies. Use the
available osx_ldflags already detected earlier in the process.
Resolve "g_date_time_format() does not return UTF-8 if LC_TIME is not UTF8 but other locale settings are UTF-8"
Closes#2055
See merge request GNOME/glib!1777
Make msvc_recommended_pragmas.h work better with clang-cl so that we can
use that to eliminate some warnings that are emitted as it also consumes
Microsoft compiler and SDK headers.
Also, for GLib builds, force-include msvc_recommended_pragmas.h for
clang-cl builds as well, as it becomes usable and useful there.
Fixes issue #2357.
Functions (_g_get_time_charset and _g_get_ctype_charset) to get LC_TIME and LC_CTYPE charset
by using nl_langinfo with _NL_TIME_CODESET and CODESET).
Another functions (_g_locale_time_to_utf8 and _g_locale_ctype_to_utf8) which uses thel and format
the input string accordingly.
Add new test cases with mixing UTF8 and non UTF8 LC_TIME along with UTF8
and non UTF8 LC_MESSAGES.
Closed#2055
Signed-off-by: Frederic Martinsons <frederic.martinsons@sigfox.com>
This will require distributions to ensure they pass
`--localstatedir=/var` correctly to Meson, but they should be doing that
already.
See https://mesonbuild.com/Builtin-options.html#directories for details
about how Meson treats `localstatedir` differently from most other `dir`
variables.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Meson incorrectly detects strcasecmp, strncasecmp on clang-cl if 'prefix:'
is not specified for cc.has_function().
See https://github.com/mesonbuild/meson/issues/5628
Fixes https://gitlab.gnome.org/GNOME/glib/-/issues/2337
Before this change:
msvc was using _stricmp()
gcc on mingw was using strcasecmp()
gcc on linux was using strcasecmp()
clang-cl was trying to use strcasecmp()
After this change:
msvc is using _stricmp()
gcc on mingw is using strcasecmp()
gcc on linux is using strcasecmp()
clang-cl is using _stricmp()
Tests are still failing to build with clang-cl, but that's a separate issue.
With bash completion version lesser than 2.10, only prefix is defined
while for greater version it is datadir.
Closes#1054
Signed-off-by: Frederic Martinsons <frederic.martinsons@sigfox.com>
The function declaration we use changed a bit since then.
In particular, some arguments became const. See following commit.
libselinux-2.2 was released on 20131030, and is widely available in
all major stable distributions.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
It’s landed in kernel 5.9: http://lkml.iu.edu/hypermail/linux/kernel/2008.0/02649.html
Note, this is untested because I currently don’t have kernel 5.9. We can
fix anything up if it breaks once the new syscall is wrapped in glibc.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
This currently just implements the same functionality as the existing
`stat()`/`fstat()`/`fstatat()`/`lstat()` calls, although where a reduced
field set is requested it may return faster.
Helps: #1970
cc.has_function() provide false positive for Android-20 and earlier; the fix is in Meson 0.54.2. People attempting to cross-compile previously wouldn’t have been able to get it to work without manual intervention, so the dependency bump for this platform is not an additional obstacle for them.
In cases where performance are critical it can be useful to disable
checks and asserts. GStreamer has those options too, using the same name
and setting them yielding means we can set those options on the main
project (e.g. gst-build) and glib will inherit the same value when built
as subproject.
`get_option('buildtype')` will return `'custom'` for most combinations
of `-Doptimization` and `-Ddebug`, but those two will always be set
correctly if only `-Dbuildtype` is set. So we should look at those
options directly.
For the two-way mapping between `buildtype` and `optimization`
+ `debug`, see this table:
https://mesonbuild.com/Builtin-options.html#build-type-options
The test code can be built on Windows using Cygwin or MSYS2.
Even though it's test code, it might bring assertion dialog box
for native Windows while meson configure.
There were a couple of custom paths which could end up being relative,
rather than absolute, due to not properly prefixing them with
`get_option('prefix')`.
The use of `join_paths()` here correctly drops all path components
before the final absolute path in the list of arguments. So if someone
configures GLib with an absolute path for `gio_module_dir`, that will be
used unprefixed; but if someone configures with a relative path, it will
be prefixed by `get_option('prefix)`.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Fixes: #1919
This is required to be able to build the doc. The debian docker is still
pinned to 0.49.2 which ensure we can build with both versions of meson.
Meson 0.52.0 warns about adding -Wall flag manually, we can remove that
because warning_level=1 (the default) option already implies it.
By default (on POSIX) we would be inheriting thread priorities from the
thread that pushed a new task on non-exclusive thread pools and causes a
new thread to be created. This can cause any non-exclusive thread pool
to accidentally contain threads of different priorities, or e.g. threads
with real-time priority.
To prevent this, custom handling for setting the scheduler settings for
Linux and Windows is added and as a fallback for other platforms a new
thread is added that is responsible for spawning threads for
non-exclusive thread pools.
Fixes https://gitlab.gnome.org/GNOME/glib/issues/1834
It's not supported on macOS' clang compiler and will fail the visibility
check and thus make the G_GNUC_INTERNAL attribute do nothing.
Compiler stderr:
/var/folders/nt/j2v2x4wd5cl33fq27mm31mwc0000gn/T/tmpxxf2zzi_/testfile.c:13:19: error: target does not support 'protected' visibility; using 'default' [-Werror,-Wunsupported-visibility]
__attribute__ ((visibility ("protected")))
^
1 error generated.
Checking if "GNU C visibility attributes test" compiles: NO
When choosing the type to base `size_t` on, check the compatibility of
passing pointers, as well as the width of the type, to avoid compiler
warnings in future.
For now, the code to do the checks is fairly ugly due to limitations in
Meson. In particular, the new checks are limited to gcc and clang (other
compilers will behave as before), and they are all duplicated. See the
comments in the code for links to Meson improvement requests.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Fixes: #1777
If we're cross-compiling, the installed-tests are useful even if we
can't run them on the build machine: we can copy them to the host
machine (possibly via a distro package like Debian's libglib2.0-tests)
and run them there.
While I'm changing the build-tests condition anyway, deduplicate it.
Based on a patch by Helmut Grohne.
Bug-Debian: https://bugs.debian.org/941509
Signed-off-by: Simon McVittie <smcv@collabora.com>
We already depend on Meson 0.49.2, which depends on Python 3.5, so we’ve
actually implicitly had this requirement for a while. Might as well make
it explicit.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Instead of letting each directory to find its way to link with libdl,
it is easier to put the check in the top level, so its result can be
used by all directories.
It is a follow-up of https://gitlab.gnome.org/GNOME/glib/merge_requests/810.
Also set the Windows version to be 10 or newer when targeting UWP, since
the Windows 8 SDK does not have many of the APIs we need, such as
_beginthreadex.
We cannot bump to the latest stable version of Meson, even if it would
make our life easier. We can, though, use the version of Meson shipped
by the next, soon to be released Debian stable.
We're using the `install` argument for configure_file() all over the
place.
The support for an `install` argument for configure_file() was added in
Meson 0.50, but we haven't bumped the minimum version of Meson we
require, yet; which means we're getting compatibility warnings when
using recent versions of Meson, and undefined behaviour when using older
versions.
The configure_file() object defaults to `install: false`, unless an
install directory is used. This means that all instances of an `install`
argument with an explicit `true` or `false` value can be removed,
whereas all instances of `install` with a value determined from a
configuration option must be turned into an explicit conditional.
The plugin modules in these tests get statically linked with a separate
copy of GLib so they end up calling vfuncs in their own copy of GLib.
Fixes#1648
GLib checks for __sync_bool_compare_and_swap, and requires
__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 to be defined if the function is available,
except with special cases like Linux armv5.
Extend the existing workaround to unbreak on old gcc versions that implement
__sync_bool_compare_and_swap but don't provide __GCC_HAVE_* macros.
We need to enable building the dirent and gnulib sources for clang-cl,
as we are still using the Microsoft-style headers and lib's and CRT.
We need to also do this for the following, for similar reasoning:
-Symbol export (via __declspec(dllexport))
-Dependency discovery without pkg-config files
-long long and ssize_t detection
We do, however, enable the autoptr tests for clang-cl builds. Note that
at this point real MSVC builds are still better supported than clang-cl
builds, and it will likely remain so for at least the near future,
alhtough real MSVC builds of the GTK stack are consumable and are usable
by clang-cl.
We are still seeing occasional CI failures due to timeouts when heavily
loaded. It’s best to wait a little longer than to throw all the results
out when they’re almost done.
For example, see https://gitlab.gnome.org/tristan957/glib/-/jobs/331330.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
The code in gunicollate uses __STDC_ISO_10646__ to check that wchar.h is avilable,
that it includes the wide character related functions and that sizeof(wchar_t) == 4.
cygwin defines __STDC_ISO_10646__ and has sizeof(wchar_t) == 2 and the C standard text isn't
that clear on whether wchar_t should always be 4 bytes in this case, so we better not use if for
assuming the size here.
Instead of relying on __STDC_ISO_10646__ add HAVE_WCHAR_H and SIZEOF_WCHAR_T macros.
With HAVE_WCHAR_H defined we assume wchar_t exists and wchar.h exists. With SIZEOF_WCHAR_T we
guard the parts where the size of wchar_t is assumed to be 4 (currently all of them).
Note that this doesn't make the collate tests pass under cygwin, they fail before and after this patch for me.
See !755 for related discussions.
The correct spelling is "_NL_ABALTMON_n" rather than "_NL_ALTMON_n".
The typo made Meson build think that _NL_ABALTMON_n constants are
not supported which was totally wrong. This made g_date_time_format()
output incorrect abbreviated month names in some languages.
The old configure.ac script was correct here.
Bug introduced in commit be4f96b650.
Closes: #1759
