Cleans up/renames as private some internal var definitions, removes some fucked uses of internal list vars (#75769)

## About The Pull Request

[Improves the documentation of DCS lists, removes old list of callback
docs that no longer
apply](https://github.com/tgstation/tgstation/commit/c3821d9f5ffaeaa4772f927c819da0c1de0ca27c)

[Adds a second signal register to decal rotating, adds a trait to
objects under a tile. STOP DIRECTLY READING HIDDEN LISTS I SWEAR TO
GOD](https://github.com/tgstation/tgstation/commit/6b3f97a76a6f7d24ab952739a1561633922994e1)

[Removes direct reads of the timer list, they were redundant
mostly](https://github.com/tgstation/tgstation/commit/14fcd9f8a6d1b2d42ec6df3493ebc76fe7c12032)

[Please stop directly reading/modifying the traits list to ensure your
dna rot follows the
brain](https://github.com/tgstation/tgstation/commit/ec0e5237ec2b7c3b7806cb993670acc8ce388bdc)

[Marks internal datum lists as well internal with
_](https://github.com/tgstation/tgstation/pull/75769/commits/57c6577ff61629b8ea792ee37ec4f2490a8e2865)

[57c6577](https://github.com/tgstation/tgstation/pull/75769/commits/57c6577ff61629b8ea792ee37ec4f2490a8e2865)

Does the same to _clear_signal_refs() in hopes of keeping people from
touching it

## Why It's Good For The Game

They pissed me off.

Users should not be touching these lists, especially in ways that make
assumptions about their structure and are thus prone to breaking if that
ever changes.
Most of these are close to zero cost changes, using a wrapper to solve
the problem, or just yeeting it

Two aren't, Decals with a direction have gained a second signal register
on init, and things that sit underfloor (cables/pipes) now get a trait
when inserted there.

This should have a minimal impact on memory/init time, bugging
@Mothblocks about it just in case

code/datums/components/_component.dm

@@ -90,9 +90,9 @@
 /datum/component/proc/_JoinParent()
 	var/datum/P = parent
 	//lazy init the parent's dc list
-	var/list/dc = P.datum_components
+	var/list/dc = P._datum_components
 	if(!dc)
-		P.datum_components = dc = list()
+		P._datum_components = dc = list()
 
 	//set up the typecache
 	var/our_type = type
@@ -127,7 +127,7 @@
  */
 /datum/component/proc/_RemoveFromParent()
 	var/datum/parent = src.parent
-	var/list/parents_components = parent.datum_components
+	var/list/parents_components = parent._datum_components
 	for(var/I in _GetInverseTypeList())
 		var/list/components_of_type = parents_components[I]
 
@@ -143,7 +143,7 @@
 			parents_components -= I
 
 	if(!parents_components.len)
-		parent.datum_components = null
+		parent._datum_components = null
 
 	UnregisterFromParent()
 
@@ -220,9 +220,9 @@
 		RegisterSignals(target, signal_type, proctype, override)
 		return
 
-	var/list/procs = (signal_procs ||= list())
+	var/list/procs = (_signal_procs ||= list())
 	var/list/target_procs = (procs[target] ||= list())
-	var/list/lookup = (target.comp_lookup ||= list())
+	var/list/lookup = (target._comp_lookup ||= list())
 
 	if(!override && target_procs[signal_type])
 		var/override_message = "[signal_type] overridden. Use override = TRUE to suppress this warning.\nTarget: [target] ([target.type]) Proc: [proctype]"
@@ -258,13 +258,13 @@
  * * sig_typeor_types Signal string key or list of signal keys to stop listening to specifically
  */
 /datum/proc/UnregisterSignal(datum/target, sig_type_or_types)
-	var/list/lookup = target.comp_lookup
-	if(!signal_procs || !signal_procs[target] || !lookup)
+	var/list/lookup = target._comp_lookup
+	if(!_signal_procs || !_signal_procs[target] || !lookup)
 		return
 	if(!islist(sig_type_or_types))
 		sig_type_or_types = list(sig_type_or_types)
 	for(var/sig in sig_type_or_types)
-		if(!signal_procs[target][sig])
+		if(!_signal_procs[target][sig])
 			if(!istext(sig))
 				stack_trace("We're unregistering with something that isn't a valid signal \[[sig]\], you fucked up")
 			continue
@@ -272,25 +272,25 @@
 			if(2)
 				lookup[sig] = (lookup[sig]-src)[1]
 			if(1)
-				stack_trace("[target] ([target.type]) somehow has single length list inside comp_lookup")
+				stack_trace("[target] ([target.type]) somehow has single length list inside _comp_lookup")
 				if(src in lookup[sig])
 					lookup -= sig
 					if(!length(lookup))
-						target.comp_lookup = null
+						target._comp_lookup = null
 						break
 			if(0)
 				if(lookup[sig] != src)
 					continue
 				lookup -= sig
 				if(!length(lookup))
-					target.comp_lookup = null
+					target._comp_lookup = null
 					break
 			else
 				lookup[sig] -= src
 
-	signal_procs[target] -= sig_type_or_types
-	if(!signal_procs[target].len)
-		signal_procs -= target
+	_signal_procs[target] -= sig_type_or_types
+	if(!_signal_procs[target].len)
+		_signal_procs -= target
 
 /**
  * Called on a component when a component of the same type was added to the same parent
@@ -354,17 +354,17 @@
  * Use the [SEND_SIGNAL] define instead
  */
 /datum/proc/_SendSignal(sigtype, list/arguments)
-	var/target = comp_lookup[sigtype]
+	var/target = _comp_lookup[sigtype]
 	if(!length(target))
 		var/datum/listening_datum = target
-		return NONE | call(listening_datum, listening_datum.signal_procs[src][sigtype])(arglist(arguments))
+		return NONE | call(listening_datum, listening_datum._signal_procs[src][sigtype])(arglist(arguments))
 	. = NONE
 	// This exists so that even if one of the signal receivers unregisters the signal,
 	// all the objects that are receiving the signal get the signal this final time.
 	// AKA: No you can't cancel the signal reception of another object by doing an unregister in the same signal.
 	var/list/queued_calls = list()
 	for(var/datum/listening_datum as anything in target)
-		queued_calls[listening_datum] = listening_datum.signal_procs[src][sigtype]
+		queued_calls[listening_datum] = listening_datum._signal_procs[src][sigtype]
 	for(var/datum/listening_datum as anything in queued_calls)
 		. |= call(listening_datum, queued_calls[listening_datum])(arglist(arguments))
 
@@ -381,7 +381,7 @@
 	RETURN_TYPE(c_type)
 	if(initial(c_type.dupe_mode) == COMPONENT_DUPE_ALLOWED || initial(c_type.dupe_mode) == COMPONENT_DUPE_SELECTIVE)
 		stack_trace("GetComponent was called to get a component of which multiple copies could be on an object. This can easily break and should be changed. Type: \[[c_type]\]")
-	var/list/dc = datum_components
+	var/list/dc = _datum_components
 	if(!dc)
 		return null
 	. = dc[c_type]
@@ -401,7 +401,7 @@
 	RETURN_TYPE(c_type)
 	if(initial(c_type.dupe_mode) == COMPONENT_DUPE_ALLOWED || initial(c_type.dupe_mode) == COMPONENT_DUPE_SELECTIVE)
 		stack_trace("GetComponent was called to get a component of which multiple copies could be on an object. This can easily break and should be changed. Type: \[[c_type]\]")
-	var/list/dc = datum_components
+	var/list/dc = _datum_components
 	if(!dc)
 		return null
 	var/datum/component/C = dc[c_type]
@@ -419,7 +419,7 @@
  * * c_type The component type path
  */
 /datum/proc/GetComponents(c_type)
-	var/list/components = datum_components?[c_type]
+	var/list/components = _datum_components?[c_type]
 	if(!components)
 		return list()
 	return islist(components) ? components : list(components)
@@ -590,7 +590,7 @@
  * * /datum/target the target to move the components to
  */
 /datum/proc/TransferComponents(datum/target)
-	var/list/dc = datum_components
+	var/list/dc = _datum_components
 	if(!dc)
 		return
 	var/comps = dc[/datum/component]

code/datums/components/food/decomposition.dm

@@ -89,10 +89,18 @@
 	remove_timer()
 	return ..()
 
+/// Returns the time remaining in decomp, either from our potential timer or our own value, whichever is more useful
+/datum/component/decomposition/proc/get_time()
+	if(!timerid)
+		return time_remaining
+	return timeleft(timerid)
+
 /datum/component/decomposition/proc/remove_timer()
-	if(active_timers) // Makes sure there's an active timer to delete.
-		time_remaining = timeleft(timerid)
-		deltimer(timerid)
+	if(!timerid)
+		return
+	time_remaining = timeleft(timerid)
+	deltimer(timerid)
+	timerid = null
 
 /datum/component/decomposition/proc/dropped()
 	SIGNAL_HANDLER
@@ -118,11 +126,7 @@
 
 /datum/component/decomposition/proc/examine(datum/source, mob/user, list/examine_list)
 	SIGNAL_HANDLER
-	var/time_d = 0
-	if(active_timers) // Is the timer currently applied to this?
-		time_d = timeleft(timerid)
-	else
-		time_d = time_remaining
+	var/time_d = get_time()
 	switch(time_d / original_time)
 		if(0.5 to 0.75) // 25% rotten
 			examine_list += span_notice("[parent] looks kinda stale.")

code/datums/components/plumbing/_plumbing.dm

@@ -63,6 +63,7 @@
 /datum/component/plumbing/UnregisterFromParent()
 	UnregisterSignal(parent, list(COMSIG_MOVABLE_MOVED, COMSIG_PARENT_QDELETING, COMSIG_OBJ_DEFAULT_UNFASTEN_WRENCH, COMSIG_OBJ_HIDE, \
 	COMSIG_ATOM_UPDATE_OVERLAYS, COMSIG_ATOM_DIR_CHANGE, COMSIG_MOVABLE_CHANGE_DUCT_LAYER, COMSIG_COMPONENT_ADDED))
+	REMOVE_TRAIT(parent, TRAIT_UNDERFLOOR, REF(src))
 
 /datum/component/plumbing/Destroy()
 	ducts = null
@@ -316,6 +317,11 @@
 
 	var/should_hide = !underfloor_accessibility
 
+	if(should_hide)
+		ADD_TRAIT(parent_obj, TRAIT_UNDERFLOOR, REF(src))
+	else
+		REMOVE_TRAIT(parent_obj, TRAIT_UNDERFLOOR, REF(src))
+
 	if(parent_movable.anchored || !should_hide)
 		tile_covered = should_hide
 		parent_obj.update_appearance()

code/datums/datum.dm

@@ -18,24 +18,24 @@
 	var/gc_destroyed
 
 	/// Active timers with this datum as the target
-	var/list/active_timers
+	var/list/_active_timers
 	/// Status traits attached to this datum. associative list of the form: list(trait name (string) = list(source1, source2, source3,...))
-	var/list/status_traits
+	var/list/_status_traits
 
 	/**
 	  * Components attached to this datum
 	  *
-	  * Lazy associated list in the structure of `type:component/list of components`
+	  * Lazy associated list in the structure of `type -> component/list of components`
 	  */
-	var/list/datum_components
+	var/list/_datum_components
 	/**
 	  * Any datum registered to receive signals from this datum is in this list
 	  *
-	  * Lazy associated list in the structure of `signal:registree/list of registrees`
+	  * Lazy associated list in the structure of `signal -> registree/list of registrees`
 	  */
-	var/list/comp_lookup
-	/// Lazy associated list in the structure of `signals:proctype` that are run when the datum receives that signal
-	var/list/list/datum/callback/signal_procs
+	var/list/_comp_lookup
+	/// Lazy associated list in the structure of `target -> list(signal -> proctype)` that are run when the datum receives that signal
+	var/list/list/_signal_procs
 
 	/// Datum level flags
 	var/datum_flags = NONE
@@ -107,9 +107,9 @@
 	datum_flags &= ~DF_USE_TAG //In case something tries to REF us
 	weak_reference = null //ensure prompt GCing of weakref.
 
-	if(active_timers)
-		var/list/timers = active_timers
-		active_timers = null
+	if(_active_timers)
+		var/list/timers = _active_timers
+		_active_timers = null
 		for(var/datum/timedevent/timer as anything in timers)
 			if (timer.spent && !(timer.flags & TIMER_DELETE_ME))
 				continue
@@ -122,7 +122,7 @@
 	#endif
 
 	//BEGIN: ECS SHIT
-	var/list/dc = datum_components
+	var/list/dc = _datum_components
 	if(dc)
 		var/all_components = dc[/datum/component]
 		if(length(all_components))
@@ -133,15 +133,15 @@
 			qdel(C, FALSE, TRUE)
 		dc.Cut()
 
-	clear_signal_refs()
+	_clear_signal_refs()
 	//END: ECS SHIT
 
 	return QDEL_HINT_QUEUE
 
 ///Only override this if you know what you're doing. You do not know what you're doing
 ///This is a threat
-/datum/proc/clear_signal_refs()
-	var/list/lookup = comp_lookup
+/datum/proc/_clear_signal_refs()
+	var/list/lookup = _comp_lookup
 	if(lookup)
 		for(var/sig in lookup)
 			var/list/comps = lookup[sig]
@@ -151,10 +151,10 @@
 			else
 				var/datum/component/comp = comps
 				comp.UnregisterSignal(src, sig)
-		comp_lookup = lookup = null
+		_comp_lookup = lookup = null
 
-	for(var/target in signal_procs)
-		UnregisterSignal(target, signal_procs[target])
+	for(var/target in _signal_procs)
+		UnregisterSignal(target, _signal_procs[target])
 
 #ifdef DATUMVAR_DEBUGGING_MODE
 /datum/proc/save_vars()

code/datums/elements/decals/_decal.dm

@@ -20,23 +20,17 @@
 
 	if(old_dir == new_dir)
 		return
-	var/list/resulting_decals_params = list() // param lists
-	var/list/old_decals = list() //instances
 
-	if(!source.comp_lookup || !source.comp_lookup[COMSIG_ATOM_UPDATE_OVERLAYS])
-		//should probably also unregister itself
+	var/list/datum/element/decal/old_decals = list() //instances
+	SEND_SIGNAL(source, COMSIG_ATOM_DECALS_ROTATING, old_decals)
+
+	if(!length(old_decals))
+		UnregisterSignal(source, COMSIG_ATOM_DIR_CHANGE)
 		return
 
-	if(length(source.comp_lookup[COMSIG_ATOM_UPDATE_OVERLAYS]))
-		for(var/datum/element/decal/decal in source.comp_lookup[COMSIG_ATOM_UPDATE_OVERLAYS])
-			old_decals += decal
-			resulting_decals_params += list(decal.get_rotated_parameters(old_dir,new_dir))
-	else
-		var/datum/element/decal/decal = source.comp_lookup[COMSIG_ATOM_UPDATE_OVERLAYS]
-		if(!istype(decal))
-			return
-		old_decals += decal
-		resulting_decals_params += list(decal.get_rotated_parameters(old_dir,new_dir))
+	var/list/resulting_decals_params = list() // param lists
+	for(var/datum/element/decal/rotating as anything in old_decals)
+		resulting_decals_params += list(rotating.get_rotated_parameters(old_dir,new_dir))
 
 	//Instead we could generate ids and only remove duplicates to save on churn on four-corners symmetry ?
 	for(var/datum/element/decal/decal in old_decals)
@@ -80,7 +74,7 @@
 	base_icon_state = _icon_state
 	smoothing = _smoothing
 
-	RegisterSignal(target,COMSIG_ATOM_UPDATE_OVERLAYS, PROC_REF(apply_overlay), TRUE)
+	RegisterSignal(target, COMSIG_ATOM_UPDATE_OVERLAYS, PROC_REF(apply_overlay), TRUE)
 	if(target.flags_1 & INITIALIZED_1)
 		target.update_appearance(UPDATE_OVERLAYS) //could use some queuing here now maybe.
 	else
@@ -88,7 +82,8 @@
 	if(isitem(target))
 		INVOKE_ASYNC(target, TYPE_PROC_REF(/obj/item/, update_slot_icon), TRUE)
 	if(_dir)
-		SSdcs.RegisterSignal(target,COMSIG_ATOM_DIR_CHANGE, TYPE_PROC_REF(/datum/controller/subsystem/processing/dcs, rotate_decals), TRUE)
+		RegisterSignal(target, COMSIG_ATOM_DECALS_ROTATING, PROC_REF(shuttle_rotate), TRUE)
+		SSdcs.RegisterSignal(target, COMSIG_ATOM_DIR_CHANGE, TYPE_PROC_REF(/datum/controller/subsystem/processing/dcs, rotate_decals), override=TRUE)
 	if(!isnull(_smoothing))
 		RegisterSignal(target, COMSIG_ATOM_SMOOTHED_ICON, PROC_REF(smooth_react), TRUE)
 	if(_cleanable)
@@ -160,6 +155,10 @@
 	Detach(source)
 	new_turf.AddElement(type, pic.icon, base_icon_state, directional, pic.plane, pic.layer, pic.alpha, pic.color, smoothing, cleanable, description)
 
+/datum/element/decal/proc/shuttle_rotate(datum/source, list/datum/element/decal/rotating)
+	SIGNAL_HANDLER
+	rotating += src
+
 /**
  * Reacts to the source atom smoothing.
  *

code/datums/elements/undertile.dm

@@ -42,6 +42,7 @@
 
 	if(underfloor_accessibility < UNDERFLOOR_INTERACTABLE)
 		SET_PLANE_IMPLICIT(source, FLOOR_PLANE) // We do this so that turfs that allow you to see what's underneath them don't have to be on the game plane (which causes ambient occlusion weirdness)
+		ADD_TRAIT(source, TRAIT_UNDERFLOOR, REF(src))
 
 		if(tile_overlay)
 			T.add_overlay(tile_overlay)
@@ -58,6 +59,7 @@
 
 	else
 		SET_PLANE_IMPLICIT(source, initial(source.plane))
+		REMOVE_TRAIT(source, TRAIT_UNDERFLOOR, REF(src))
 
 		if(invisibility_trait)
 			REMOVE_TRAIT(source, invisibility_trait, ELEMENT_TRAIT(type))