"Passengers intended for a building that has been deleted" warning

[Matthew]

Steps to reproduce
1. Run Simutrans-Extended with the parameters -log -debug 2 and pak128.Britain-Ex
2. Load any save with a large rail freight network and a large passenger network.
3. Allow the game to run for a minute and then examine the log.

Expected results
There are no errors or warnings in the log.

Actual results
Variations on the following warning appear frequently in the log:

Code Select Expand

Warning: haltestelle_t::liefere_an():   1 Passengers delivered to Brownchurch Railway Station were intended for a building that has been deleted.
Observations
With help from Prissi, I modded the game to also log the intended destination of the passengers, i.e. the building that has allegedly been deleted.

I carefully studied a sample of about thirty log entries, and then visually scanned the rest of the entries for similar co-ordinates. It appears that all of the intended destinations are freight platform buildings with commuter jobs, such as the Goods Shed or the Goods Siding with Crane. There were no passenger buildings, and no station extension buildings either. All of these buildings had 100% Jobs Available vacant, even in cities where passenger station extension buildings had all their jobs filled.

The intended destination was not the stop where passengers had been delivered (according to the log) in any of the ~thirty messages that I looked at. But I did not check every log message for this, and only a tiny minority of the stops on the test map have both freight and passengers, so this might be happening elsewhere.

But there were also apparently identical freight platform buildings at other stops on the same map, which never appeared in the log with this warning. In the handful of unaffected platforms that I looked at, 100% of the Jobs Available  were filled. So this warning doesn't seem to be a problem with passengers travelling to freight platforms in general; only a subset are affected.

This might just be the normal random variation within the passenger generation system.

Nonetheless, I have tried to find a pattern distinguishing the two groups. I've ruled out direction and whether the stop is freight-only. Many of the platform buildings affected by the warning are on tiles that have been terraformed or where the platform rests on piers. It's possible that all of them are, but I can't remember exactly how all these stations were built. If that is the pattern, then height could be a factor (e.g. wrong koord3d). I could not find any messages in the log about freight platforms on tiles that have always been flat. But I'm very uncertain about this factor. As well as the uncertain history of the logged tiles, this test run only had 415 warning messages, and there is a high level of randomness in passenger generation anyway. Readers are responsible for their own decisions about whether to investigate this possibility.

The other obvious factor to look into is whether the freight platforms that got the warning really are the ones that had buildings that have been deleted. But at least some of them are outside city limits, which rules out citybuildings. I wouldn't have replaced industries with platforms except for farms fields, and there are platforms built in place of fields that are not affected. It's just possible that in some cases the tiles have been upgraded from a basic Goods Siding (with 0 freight capacity and 0 employment_capacity) to a more developed platform, but a basic Goods Siding should not be a passenger destination at all. And it would have been in-game years since the upgrade, so these are not just passengers left in limbo by a recent change. I might try to note such upgrades in future to definitely rule out this possibility.

However, I'm probably not going to investigate this further now, as I was mainly investigating to make sure it wasn't related to another, more annoying, bug.

If anyone else wants to investigate, they might be interested in some other relevant forum threads that I found while searching for existing bug reports. This bug report from 2021 has the same warning appearing in a B-B log. Isidoro has written an overview of Standard's version of this function and another thread has more comments explaining how this function worked.