[0.12.29] [kovarex] Furnace doesn't update output when input changed

[JasonC]

Discovered a minor issue while experimenting with something else. It's easier just to explain the steps than try to summarize:

Steps:

1. Make sure detail view is on.
2. Place a furnace (any kind) on the map. Do not add fuel.
3. Place some resources in its input slot (for example: copper ore). Observe that the detail graphic for its output displays (for example: copper plate).
4. Now replace the resource with something else (for example: iron ore).

Expected: Output detail graphic switches to the result for the new resource (for example: iron plate).

Actual: Output detail graphic never changes (with the example, it stays a picture of a copper plate even though there's iron ore in it now).

The situation resolves immediately and the correct graphic is displayed as soon as you add fuel in (in example, as soon as fuel is added furnace will start producing an iron plate and graphic will change to iron plate).

Now, I did some extra experiments with inserters, similar to what I did here (which is where I discovered this). I have found that the above is not just a graphical issue, but is an issue with the furnace's perceived output. Perform the following steps:

1. Turn on detail view.
2. Place a furnace (any kind) on the map. Do not add fuel.
3. Place copper ore in the furnaces input slot. Output graphic changes to copper plate.
4. Replace input with iron ore. Output graphic remains copper plate, as described above.
5. Now, with the furnace in this state, attempt to insert copper ore with an inserter.

Expected: Inserter does not pick up copper ore.

Actual: Inserter picks up copper and gets stuck, because even though there's iron ore in the furnace, the furnace still thinks its output is copper plate (because of above issue), and the inserter thinks it can insert copper (inserter decisions are governed by furnace's output, not its input, as detailed in the post I linked to earlier -- be aware this is not the same issue being described in that post, this has nothing to do with multi-resource recipes and such).

Other weird things along those lines happen. For example, if you put in copper ore (so the output changes to copper plate), then replace it with iron ore (output still thinks its copper plate), then attempt to insert iron with an inserter, it won't pick the iron up at all since the furnace still thinks its going to output a copper plate despite it being loaded with iron ore.

As far as I can tell, though, nothing else weird seems to happen -- the furnace still produces the correct resource, etc. It's also pretty minor since you don't really encounter this during typical game play, it's really an edge case, and the situation resolves immediately as soon as things start flowing (as soon as you fuel the furnace everything returns to normal right away).

[kovarex]

Ok, as it still works properly as long long as there is power, I'm going to leave it as it is, as the change would make it little bit slower.