Allow transitions in callbacks

[annismckenzie]

This fixes looplab#43 and looplab#61.

This contains breaking changes, namely:

• signature change of fsm.Event() from name string, ...args to ctx context.Context, name string, ...args
• signature change of event handlers from e *fsm.Event to ctx context.Context, e *fsm.Event (refs Context in event handlers looplab/fsm#61)

This allows state transitions to happen in enter state and after event callbacks:

fsm/fsm_test.go

Lines 672 to 711 in d8a0147

	func TestTransitionInCallbacks(t *testing.T) {
	var fsm *FSM
	var afterFinishCalled bool
	fsm = NewFSM(
	"start",
	Events{
	{Name: "run", Src: []string{"start"}, Dst: "end"},
	{Name: "finish", Src: []string{"end"}, Dst: "finished"},
	{Name: "reset", Src: []string{"end", "finished"}, Dst: "start"},
	},
	Callbacks{
	"enter_end": func(ctx context.Context, e *Event) {
	if err := e.FSM.Event(ctx, "finish"); err != nil {
	fmt.Println(err)
	}
	},
	"after_finish": func(ctx context.Context, e *Event) {
	afterFinishCalled = true
	if e.Src != "end" {
	panic(fmt.Sprintf("source should have been 'end' but was '%s'", e.Src))
	}
	if err := e.FSM.Event(ctx, "reset"); err != nil {
	fmt.Println(err)
	}
	},
	},
	)
	if err := fsm.Event(context.Background(), "run"); err != nil {
	t.Errorf("expected no error, got %v", err)
	}
	if !afterFinishCalled {
	t.Error("expected after_finish callback to have been executed but it wasn't")
	}
	currentState := fsm.Current()
	if currentState != "start" {
	t.Errorf("expected state to be 'start', was '%s'", currentState)
	}
	}

[coveralls]

Pull Request Test Coverage Report for Build 2761186635

• 49 of 51 (96.08%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 93.735%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
uncancel_context.go	4	6	66.67%

Totals
Change from base Build 2761174425:	0.1%
Covered Lines:	404
Relevant Lines:	431

---

💛 - Coveralls

[annismckenzie]

With looplab#82 merged I can now open a new PR against upstream – closing.