Add null sentinel to null-terminated array of pointers

[Gothem]

Currently the bindings define them as [*]*T pointers (for example in gio.DBusSignalInfo), when in reality they should be [*:null]?*T.

This prevents Segfaults when programs expect the arrays to terminate with null.

[ianprime0509]

Thanks for the report! Unfortunately this looks like an upstream issue with the GIR: here's what the signals field of DBusInterfaceInfo looks like as of the GNOME 46 SDK (I think this is what you're referring to):

      <field name="signals" writable="1">
        <doc xml:space="preserve"
             filename="gio/gdbusintrospection.h"
             line="143">A pointer to a %NULL-terminated array of pointers to #GDBusSignalInfo structures or %NULL if there are no signals.</doc>
        <array c:type="GDBusSignalInfo**">
          <type name="DBusSignalInfo" c:type="GDBusSignalInfo*"/>
        </array>
      </field>

Although the documentation mentions this is a null-terminated array, the array type here is missing zero-terminated="1" which would allow the translate-gir logic to create the appropriate type.

A case where this is marked up correctly in GIR is the return value of g_desktop_app_info_get_string_list:

        <return-value transfer-ownership="full">
          <doc xml:space="preserve"
               filename="gio/gdesktopappinfo.c"
               line="5106">
 a %NULL-terminated string array or %NULL if the specified
 key cannot be found. The array should be freed with g_strfreev().</doc>
          <array length="1" zero-terminated="1" c:type="gchar**">
            <type name="utf8"/>
          </array>
        </return-value>

This case is correctly translated to [*:null]?[*:0]u8:

zig-gobject/src/translate.zig

Lines 1932 to 1938 in 787a447

	try testTranslateArrayType("[*:null]?[*:0]u8", .{
	.c_type = "gchar**",
	.zero_terminated = true,
	.element = &.{
	.simple = .{ .name = .{ .ns = null, .local = "utf8" }, .c_type = null },
	},
	}, .{});

So there are a few things I'm planning to do based on this issue:

1. Look for other cases (based on the documentation) where the same problem exists, and work around them all by patching the upstream GIR files via gir-fixes.
2. Add more test coverage for translateArray just to make sure zero-terminated="1" works in other possible cases (in addition to the one mentioned above with a string array).
3. Open a tracking issue for the upstream GIR fixes that need to be made, and look into sending the corrections upstream so the gir-fixes patches can eventually be removed.