We have the following code in gstelementfactory.c, with the (gpointer) cast presumably to avoid type-punning warnings:

  if (!g_atomic_pointer_compare_and_exchange (
    (gpointer) & oclass->elementfactory, NULL, factory))

This code now asserts at compile time due to recent gatomic header changes.  We're basically trying to figure out how to not trip a warning with both new and old glib.

IRC log:

<ds> desrt: yo
<desrt> what's up?
<ds> desrt: http://pastebin.com/gaVXpbAG

gstelementfactory.c: In function ‘gst_element_factory_create’:
gstelementfactory.c:397:8: error: size of array ‘Compile_Time_Assertion’ is negative
gstelementfactory.c:397:8: error: invalid use of void expression
gstelementfactory.c:397:8: error: incompatible type for argument 1 of ‘__sync_bool_compare_and_swap’

<ds> desrt: due to your recent gatomic hacking
<ds> desrt: one problem, you changed the prototype of ..
<ds> oh wait
<ds> lemme give you some context
<ds>   if (!g_atomic_pointer_compare_and_exchange (
<ds>           (gpointer) & oclass->elementfactory, NULL, factory))
<ds> that is the code that it fails on
<desrt> that makes perfect sense
<ds> Did you intend to change the prototype of g_atomic_pointer_compare_and_exchange?
<desrt> i actually didn't
<desrt> well, i did
<desrt> but not in a way that negatively impacts you
<ds> right
<desrt> the thing that's nailing you is the fact that i introduced a macro to do some additional checks
<ds> obviously, we want to change that to (gpointer *)
<desrt> better to remove it entirely
<ds> mmm, true.  not sure why it was like that.
<desrt> without the macro the cast was required
<desrt> and as a nice side effect you got a warning about type-punned pointers
<desrt> now you just give a pointer to an arbitrary pointer-sized object and it always works
<desrt> the problem with casting to (gpointer) is that (gpointer) has no particular size
<desrt> so the check fails
<ds> yeah, i understand what is going on.  I'm just checking if you intended to break it that way.
<desrt> well
<desrt> truthfully this is an incompatible API break in GLib
<desrt> which is something that we usually strive to avoid at all costs
<ds> right
<desrt> so it might be the case that i have to fix it to unbreak you
<ds> however, if it's "we're only breaking apps where they're doing something really stupid", I don't mind
<desrt> (and possibly others)
<desrt> well....
<desrt> what you were doing is necessitated by (what i consider) a deficiency of the old API and GCC's excessively pedantic behaviour
<desrt> so it's stupid, but it's not your fault :)
<ds> trying to keep -Wall -Werror compatibility across this change might be challenging, then
<ds> ok
<desrt> indeed
<ds> fine with me.  just wanted to know what's up.  thanks.
<desrt> one thing you could do is to put brackets around the function name
<desrt> that will prevent the macro evaluation (thereby skipping the checks)
<desrt> it will also reduce performance, though, since you miss the chance at inlining that the macro gives you
<desrt> please open a bug
<desrt> i see a couple of ways out of the mess
<desrt> one of them is to drop the extra checks
<desrt> the other is only to impose the extra checks if G_DISABLE_DEPRECATED is defined
<desrt> a 3rd option is to add a G_ATOMIC_BACKCOMPT define or something like that
<desrt> so that people can have -Well -Werror compatibility across the change if they're willing to add an extra #define
<desrt> there are a lot of possibilities
<desrt> and i'd like matthias's input
<ds> we can do a glib version check, too
<desrt> true.
<desrt> a cast to (volatile gpointer *) might do the trick on both
<desrt> could give that a try...