Debugging code to trace down path_invalidate within callbacks error

advtrains/path.lua

@@ -117,6 +117,7 @@ function advtrains.path_invalidate(train)
 	train.path_req_b=0
 	
 	train.dirty = true
+	advtrains.dbg_last_pathclear = "LAST PATH_INVALIDATE: "..debug.traceback()
 end
 
 -- Prints a path using the passed print function

advtrains/trainlogic.lua

@@ -480,7 +480,11 @@ function advtrains.train_step_c(id, train, dtime)
 	run_callbacks_update(id, train)
 	
 	-- Return if something(TM) damaged the path
-	if train.no_step or train.wait_for_path or not train.path then return end
+	if not train.path then
+		atwarn(id,"@train_step_c missing path")
+		atwarn(advtrains.dbg_last_pathclear)
+		return
+	end
 	
 	advtrains.path_clear_unused(train)
 	
@@ -612,6 +616,11 @@ advtrains.te_register_on_new_path(function(id, train)
 end)
 
 advtrains.te_register_on_update(function(id, train)
+	if not train.path then
+		atwarn(id,"@register_on_update missing path")
+		atwarn(advtrains.dbg_last_pathclear)
+		return
+	end
 	local new_index = atround(train.index)
 	local new_end_index = atround(train.end_index)
 	local old_index = train.tnc.old_index