See patch. This attempts to clarify that GIOErrorEnum may be extended in the future, and that this may cause some situations that currently return G_IO_ERROR_FAILED to return a different error code. (In particular, the thing that started this was that I want to make EAFNOSUPPORT ("no support for address family") return G_IO_ERROR_NOT_SUPPORTED rather than the current value of G_IO_ERROR_FAILED.)

Note that we have done this at least once before, as seen by this code in glib-networking:

      if (g_error_matches (my_error, G_IO_ERROR, G_IO_ERROR_FAILED) ||
#if GLIB_CHECK_VERSION (2, 35, 3)
        g_error_matches (my_error, G_IO_ERROR, G_IO_ERROR_BROKEN_PIPE) ||
#endif
        ...

Besides the glib-networking example above, a grep of 'g_error_matches.*ERROR_FAILED\W' in a (not-entirely-up-to-date) checkout of jhbuild shows only two other hits:

NetworkManager comparing against G_FILE_ERROR_FAILED, but only to decide between log levels:

	if (!g_file_get_contents (path, &contents, NULL, &error)) {
		/* We assume FAILED means EOPNOTSUP */
		if (   g_error_matches (error, G_FILE_ERROR, G_FILE_ERROR_NOENT)
		    || g_error_matches (error, G_FILE_ERROR, G_FILE_ERROR_FAILED))
			debug ("error reading %s: %s", path, error->message);
		else
			error ("error reading %s: %s", path, error->message);

(and GFileError seems unlikely to ever include an error for EOPNOTSUP anyway; this code is reading from sysfs).


gcr comparing against G_SPAWN_ERROR_FAILED in a way that probably makes sense:
        if (g_error_matches (error, G_SPAWN_ERROR, G_SPAWN_ERROR_FAILED) && self->pv->first_error) {
                g_simple_async_result_set_error (res, G_SPAWN_ERROR, G_SPAWN_ERROR_FAILED,
                                                 "%s", self->pv->first_error);
                g_error_free (error);
        } else {
                g_simple_async_result_take_error (res, error);
        }