Fixes humans unable to use vehicle gunner seat

[Doubleumc]

About the pull request

Fixes #6246

Explain why it's good for the game

Vehicle gunnery is meant to be used by humans.

Testing Photographs and Procedure

Screenshots & Videos

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Changelog

🆑
fix: humans can use vehicle gunner seats again
/:cl:

[Doubleumc]

Somewhere in the mess of ishuman(), IsAdvancedToolUser(), allow_gun_usage, has_fine_manipulation, TRAIT_OPPOSABLE_THUMBS, KNOWS_TECHNOLOGY there's a good solution.

[Drulikar]

So looking at this closer, there currently appear to be side effects of us giving this trait to humans that we need to rectify. For example,

cmss13/code/datums/action.dm

Lines 189 to 195 in 1f79350

	/datum/action/item_action/can_use_action()
	if(ishuman(owner) && !owner.is_mob_incapacitated())
	var/mob/living/carbon/human/human = owner
	if(human.body_position == STANDING_UP)
	return TRUE
	if((HAS_TRAIT(owner, TRAIT_OPPOSABLE_THUMBS)) && !owner.is_mob_incapacitated())
	return TRUE

now makes it possible for humans to use actions while not standing, when that was not the case before. So this example either should refactor the other case to an else, or return FALSE if not standing. Though this proc could in general be refactored; e.g. both conditions both want is_mob_incapacitated, and body_position doesn't need to be for a human, its a living mob variable.

To me it seems like we could refactor this proc to below because I don't see much reason why xenos should be able to do this not standing up either (though I don't even know what actions this allows them to do):

	if(!HAS_TRAIT(owner, TRAIT_OPPOSABLE_THUMBS))
		return FALSE
	if(!isliving(owner))
		return FALSE
	var/mob/living/living_mob = owner
	if(living_mob.body_position != STANDING_UP)
		return FALSE
	return TRUE

So please take a look at the uses of TRAIT_OPPOSABLE_THUMBS and mitigate situations where a human would then fall into that xeno w/ thumbs case and have less restrictions, or maybe just consider fixing it the opposite way instead.

But maybe this then ought to just be a xeno exclusive trait and we just fix the opposite problems.

Also of note /mob/living/carbon/xenomorph/IsAdvancedToolUser() will currently return true for xenos w/ thumbs, but that also makes

cmss13/code/modules/projectiles/gun.dm

Line 1528 in 1f79350

if(!user.IsAdvancedToolUser() && !HAS_TRAIT(user, TRAIT_OPPOSABLE_THUMBS))

redundant...

To me it looks like these are currently problematic with the current implementation:

• /datum/action/item_action/can_use_action()
• /obj/structure/machinery/cm_vending/ui_act(action, list/params, datum/tgui/ui, datum/ui_state/state) // drops squad restriction
• /obj/structure/machinery/cm_vending/proc/can_access_to_vend(mob/user, display = TRUE, ignore_hack = FALSE) // drops all restrictions

[Doubleumc]

I agree there are likely more issues stemming from the April Fools' PR and the tangle of ishuman()/IsAdvancedToolUser()/has_fine_manipulation/TRAIT_OPPOSABLE_THUMBS cries out for a refactor, but that is way out of scope of this PR and beyond what I want to tackle at the moment.

What I have right now is:

• add the missing TRAIT_OPPOSABLE_THUMBS to the global trait list
• fix missing return in xeno buckling logic, no longer buckle twice
• remove the thumbs check entirely from vehicle seats, thumbless xenos are already prevented from using the seat earlier in the proc chain

So currently humans can use the gunner seat, thumbless xenos can't use the gunner seat, thumbed xenos can use the gunner seat.