Sam Carlberg 1021ff88a9 [cmd3] Add a declarative state machine API on top of commands v3 (#8297) ...

This provides an API for writing a finite state machine compatible with
the commands v3 framework. Individual states in the state machine are
wrappers around command objects (which may themselves be state
machines). Transitions between states are defined with a staged builder
DSL similar to command builders, and uses `@NoDiscard` to catch
partially configured transitions.

The FSM API is meant to handle highly complex cases that the fluent
command chaining DSL and coroutine-based imperative commands cannot
easily represent; specifically, where a command sequence may want to go
back to an arbitrary previous state or skip forward to an arbitrary
future state.

Here's an example from the design doc for a command that will drive to a
known scoring location, aim at a scoring target, and repeatedly shoot
balls until a storage hopper is empty. It also has conditions to stop
shooting and move back to the scoring location if it's jostled away, and
then automatically resume firing.

```java
public Command autoWithStateMachine() {
  // Declare the state machine
  StateMachine stateMachine = new StateMachine("Auto With State Machine");

  // Define states
  State getInPosition = stateMachine.addState(drivetrain.driveToScoringLocation());
  State aiming = stateMachine.addState(turret.aimAtGoal());
  State scoring = stateMachine.addState(shooter.fireOnce());
  State celebrating = stateMachine.addState(leds.celebrate());

  // Set the initial state. Neglecting this will cause a runtime exception when the state machine starts.
  // Teams using the WPILib compiler plugin will get a compiler error if they do not set this
  stateMachine.setInitialState(getInPosition);

  // Switch to aiming when we reach the scoring location.
  getInPosition.switchTo(aiming).whenComplete();
  // Set the swerve wheels in an X shape after reaching the scoring location to resist being pushed away.
  getInPosition.onExit(() -> Scheduler.getDefault().fork(drivetrain.setX()));

  // Then start scoring once the turret is aimed at the goal.
  aiming.switchTo(scoring).when(turret::aimedAtGoal);

  // Loop the scoring state as long as the hopper has a ball.
  scoring.switchTo(scoring).whenCompleteAnd(() -> hopper.hasBall());

  // Automatically interrupt any part of the aiming or scoring sequence if
  // the robot is moved away from the scoring location and move back into position.
  stateMachine.switchFromAny(aiming, scoring).to(getInPosition).when(atScoringLocation.negate());

  // Start celebrating once the final ball has been scored.
  scoring.switchTo(celebrating).whenCompleteAnd(() -> !hopper.hasBall());

  return stateMachine;
}
```

A compiler check is added to detect object construction that's not
followed by post-construction initializer methods (as defined by the
class by placing `@PostConstructionInitializer` on such methods).
`StateMachine.setInitialState` uses this to detect team code that
creates a state machine but does not set its initial state.

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..

main

[cmd3] Add a declarative state machine API on top of commands v3 (#8297)

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test/java/org/wpilib/javacplugin

[cmd3] Add a declarative state machine API on top of commands v3 (#8297)

2026-05-07 20:08:09 -07:00