[MIRROR] Fixes slimes riding monkeys and thus falling off of each other (#2576)

* Fixes slimes riding monkeys and thus falling off of each other (#55887)

Fixes slimes trying to ride monkeys.

* Fixes slimes riding monkeys and thus falling off of each other

Co-authored-by: Qustinnus <Floydje123@hotmail.com>

code/__DEFINES/traits.dm

@@ -234,6 +234,8 @@ Remember to update _globalvars/traits.dm if you're adding/removing/renaming trai
 #define TRAIT_PERMANENTLY_ONFIRE	"permanently_onfire" //overrides the update_fire proc to always add fire (for lava)
 #define TRAIT_SIGN_LANG				"sign_language" //Galactic Common Sign Language
 #define TRAIT_NANITE_MONITORING	"nanite_monitoring" //The mob's nanites are sending a monitoring signal visible on diag HUD
+/// Prevents mob from riding mobs when buckled onto something
+#define TRAIT_CANT_RIDE			"cant_ride"
 
 // You can stare into the abyss, but it does not stare back.
 // You're immune to the hallucination effect of the supermatter, either

code/datums/elements/ridable.dm

@@ -39,6 +39,9 @@
 /datum/element/ridable/proc/check_mounting(atom/movable/target_movable, mob/living/potential_rider, force = FALSE, ride_check_flags = NONE)
 	SIGNAL_HANDLER
 
+	if(HAS_TRAIT(potential_rider, TRAIT_CANT_RIDE))
+		return
+
 	var/arms_needed = 0
 	if(ride_check_flags & RIDER_NEEDS_ARMS)
 		arms_needed = 2

code/modules/mob/living/simple_animal/slime/slime.dm

@@ -86,6 +86,7 @@
 /mob/living/simple_animal/slime/Initialize(mapload, new_colour="grey", new_is_adult=FALSE)
 	var/datum/action/innate/slime/feed/F = new
 	F.Grant(src)
+	ADD_TRAIT(src, TRAIT_CANT_RIDE, INNATE_TRAIT)
 
 	is_adult = new_is_adult