AnimationNodeStateMachinePlayback.travel() gets stuck for nested state machines

[Maaack]

Godot version

4.2

System information

Linux

Issue description

A nested state machine isn't traveling to its animation in _ready() in 4.2 as it was in 4.1.3.

In the ready function, we make the root state machine travel to the state of the Stages nested state machine. Then we immediately call the Stages nested state machine to travel to Stage2. This works fine in Godot v4.1.3, but not in Godot v4.2, where it seems a delay is first needed for the second travel animation to work.

Steps to reproduce

Run the MRP below in 4.1.3 and 4.2.

In 4.1.3, the animation tree will reach Stage2 and show Finished on the screen.

In 4.2, the animation tree will only reach Stage1 and show Stuck on the screen.

Minimal reproduction project

MRP-AnimationNodeStateMachinePlayback.zip

[Maaack]

This could be related to #85600 ?

[TokageItLab]

This could be related to #85600 ?

It is totally irrelevant.

This is an unintended¹ bug, so I suspected that there was a breakdown somewhere in the 1:1 conversion of the AnimationTree and AnimationMixer blending algorithm (there were a few stinky parts, but nothing to do with this problem), but the main problem was that the travel path was generated at an unintended timing (too early) and processed twice. I am still investigating.

Footnotes

1. AnimationMixer was implemented based on AnimationTree, even though regression may occur in AnimationPlayer, AnimationTree should not ↩

[TokageItLab]

As a result, it is due to a missing test_only flag by porting that caused the travel path to be generated in situations where it should not have been. This will be fixed by #85794.