[Trains] Path Reversal

[BraveCaperCat]

Split from Train pathfinding takes much longer path by BraveCaperCat, I request that paths made by locomotives can include reversals - sudden changes in direction allowing additional paths to be made by locomotives. Here is an example of how this could help:

Image shared by BlueTemplar in "Train pathfinding takes much longer path" from which this topic was split.

two-steps_no_path.png (246.42 KiB) Viewed 175 times

The pathfinder is thinking that there's no path from Taw to the northern bridge.

Of course, as you can easily see, you can get there by going to Phyire first and then reverse course.

Two-headed trains are pretty much «second-class citizens» in Factorio, for better (general train performance, especially single-headed) or worse (these kinds of issues, which are sadly more common for new players, and also in Space Age in general (even on Nauvis, without cliff explosives ??), see also (though I haven't tried this one in 2.0 again yet)).

As shown with the above quote and image, the pathfinder cannot find a simple path which does not violate signals.
With this feature, the pathfinder would be able to find this path and therefore pathfind to it's destination.
Note that this feature cannot be applied to one-headed trains.