By doing so, we essentially cover the various compiler flags that we
want to use for non-Visual Studio builds to check for warnings that
might cause real concern.
This also skips the checks for the various GCC-isque CFlag checks that
are scattered in the various build files on Visual Studio builds, since
they are essentially meaningless on Visual Studio builds.
This enables various compiler warnings project wide and disables the triggered
ones for each library/executable. This should give us roughly the same behaviour
as with autotools.
Tested with gcc8 and clang7.
This adds the following macros and functions: GI_MAJOR_VERSION, GI_MICRO_VERSION,
GI_MINOR_VERSION, GI_CHECK_VERSION, gi_get_major_version,gi_get_micro_version,
gi_get_minor_version.
Since we share a prefix with glib we have to namespace these by using the gi_
prefix. g_gi would also work but we already export symbols with gi_ like
gi_cclosure_marshal_generic(), gi_type_tag_get_ffi_type() and
gi_type_info_extract_ffi_return_value(), so let's not add another naming scheme.
When building with Meson, we cannot set environment variables while
running custom targets and our builddir layout is different from
Autotools anyway.
Now g-ir-scanner and friends can autodetect when they're being run
uninstalled by Meson and will find _giscanner.so and the giscanner
python files in the build directory. This is very similar to what
gdbus-codegen uses in glib/gio.
Same for girepository/gdump.c.
glib_dep is what is actually needed to #include <glib.h>, not
gobject_dep. It works incidentally with system gobject/glib but not
when built via subprojects.
