Merge pull request #3899 from VOREStation/upstream-merge-5360

[MIRROR] Adds aura style modifier code

code/modules/mob/_modifiers/aura.dm

@@ -0,0 +1,18 @@
+/*
+'Aura' modifiers are semi-permanent, in that they do not have a set duration, but will expire if out of range of the 'source' of the aura.
+Note: The source is defined as an argument in New(), and if not specified, it is assumed the holder is the source,
+making it not expire ever, which is likely not what you want.
+*/
+
+/datum/modifier/aura
+	var/aura_max_distance = 5 // If more than this many tiles away from the source, the modifier expires next tick.
+
+/datum/modifier/aura/check_if_valid()
+	if(!origin)
+		expire()
+	var/atom/A = origin.resolve()
+	if(istype(A)) // Make sure we're not null.
+		if(get_dist(holder, A) > aura_max_distance)
+			expire()
+	else
+		expire() // Source got deleted or something.