Comment 126 for bug 219385

(In reply to Benjamin Otte from comment #103)
> Only if you don't compile with -DG_DISABLE_CAST_CHECKS which people
> definitely should do for releases. In that case those casts are just casts.

We compile with C flags from pkgconfig, which do not seem to include this.
I notice GTK+ does compile with -DG_DISABLE_CAST_CHECKS by default.

I don't see any documentation, but it looks like this could only help.

Seems a little strange to set an undocumented symbol that would change G_TYPE_CHECK_INSTANCE_CAST to not do what it says it does, but all g_type_check_instance_cast would do for us is print a warning (unless G_DEBUG is in the environment). It doesn't return null if the check fails.