macOS: programs using g_get_os_info() are crashing

[vmagnin]

Describe the bug
In gtk-fortran 4.2.0, examples/tests.f90, examples/bazaar.f90 and src/gtk-fortran.f90 are crashing (segmentation fault), only on macOS.

Your system:

• OS version: macOS 10.15.7
• Compiler version: gfortran
• GTK branch: gtk4, gtk-fortran 4.2.0

[vmagnin]

The problem comes from the GLib g_get_os_info() function:

call c_f_string_copy(g_get_os_info("PRETTY_NAME"//c_null_char), os_string)

The GLib doc (https://docs.gtk.org/glib/func.get_os_info.html) says it returns NULL if this information is not provided. That is the case under macOS.

[vmagnin]

Solution:

    type(c_ptr) :: ret

    ret = g_get_os_info("PRETTY_NAME"//c_null_char)
    if (c_associated(ret)) then
      call c_f_string_copy(ret, os_string)
    else
      os_string = "?"
    end if