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feat: state value added to transition type #4043

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merged 6 commits into from
Jun 6, 2023
Merged

feat: state value added to transition type #4043

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6a0f1b1
feat: state value added to transition type
May 26, 2023
3d3a385
fix: types changed
May 27, 2023
4fac6cf
change `state.matches` signature in `@xstate/fsm` to mimick the one i…
Andarist Jun 6, 2023
83ffd0c
add runtime context to what was intended to be type-only test
Andarist Jun 6, 2023
d182ddc
add default to the new type param in `Transition`
Andarist Jun 6, 2023
55cbfd7
Update .changeset/modern-spies-cry.md
Andarist Jun 6, 2023
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5 changes: 5 additions & 0 deletions .changeset/modern-spies-cry.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'@xstate/fsm': patch
---

Fixed state types when initializing the machine, as well as when switching to another state. Previously, the "string" type was used for this, which allowed any value to be passed and led to a subtle error in a running application. After this change, the error will be seen at the development stage.
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26 changes: 15 additions & 11 deletions packages/xstate-fsm/src/index.ts
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Expand Up @@ -130,7 +130,7 @@ function handleActions<
export function createMachine<
TContext extends object,
TEvent extends EventObject = EventObject,
TState extends Typestate<TContext> = { value: any; context: TContext }
TState extends Typestate<TContext> = Typestate<TContext>
>(
fsmConfig: StateMachine.Config<TContext, TEvent, TState>,
implementations: {
Expand Down Expand Up @@ -182,18 +182,21 @@ export function createMachine<

if (stateConfig.on) {
const transitions: Array<
StateMachine.Transition<TContext, TEvent>
StateMachine.Transition<TContext, TEvent, TState['value']>
> = toArray(stateConfig.on[eventObject.type]);

for (const transition of transitions) {
if (transition === undefined) {
return createUnchangedState(value, context);
}

const { target, actions = [], cond = () => true } =
typeof transition === 'string'
? { target: transition }
: transition;
const {
target,
actions = [],
cond = () => true
} = typeof transition === 'string'
? { target: transition }
: transition;

const isTargetless = target === undefined;

Expand All @@ -209,11 +212,12 @@ export function createMachine<
}

if (cond(context, eventObject)) {
const allActions = (isTargetless
? toArray(actions)
: ([] as any[])
.concat(stateConfig.exit, actions, nextStateConfig.entry)
.filter((a) => a)
const allActions = (
isTargetless
? toArray(actions)
: ([] as any[])
.concat(stateConfig.exit, actions, nextStateConfig.entry)
.filter((a) => a)
).map<StateMachine.ActionObject<TContext, TEvent>>((action) =>
toActionObject(action, (machine as any)._options.actions)
);
Expand Down
36 changes: 24 additions & 12 deletions packages/xstate-fsm/src/types.ts
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Expand Up @@ -86,10 +86,14 @@ export namespace StateMachine {
assignment: Assigner<TContext, TEvent> | PropertyAssigner<TContext, TEvent>;
}

export type Transition<TContext extends object, TEvent extends EventObject> =
| string
export type Transition<
TContext extends object,
TEvent extends EventObject,
TStateValue extends string = string
> =
| TStateValue
| {
target?: string;
target?: TStateValue;
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What exactly does this solve for you? Could you share some code that is affected by this?

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@Andarist
I decided that it would be better to show in dynamics. This file describes the state machine. The creation takes place elsewhere, here I wanted to show the development process. Please ask more questions if you need to explain in more detail what is happening in the video.

2023-05-27.13-10-34.mp4 
import { StateMachine } from '@xstate/fsm';

export type TestContext = {
  readonly value: number;
};

export type TestStateValue = 'init' | 'loading' | 'idle' | 'process';

export type TestStateMachine = StateMachine.Config<
  TestContext,
  { type: 'NEXT' | 'STOP' | 'COMPLETE' },
  { value: TestStateValue; context: TestContext }
>;

export const createStateMachine = (): TestStateMachine => ({
  context: { value: 42 },
  initial: 'init',
  states: {
    init: {
      on: {
        COMPLETE: 'loading',
      },
    },
    loading: {
      on: {
        COMPLETE: { target: 'idle' },
      },
    },
    idle: {
      on: {
        NEXT: 'process',
      },
    },
    process: {
      on: {
        STOP: { target: 'idle' },
      },
    },
  },
});

actions?: SingleOrArray<Action<TContext, TEvent>>;
cond?: (context: TContext, event: TEvent) => boolean;
};
Expand All @@ -104,9 +108,15 @@ export namespace StateMachine {
changed?: boolean | undefined;
matches: <TSV extends TState['value']>(
value: TSV
) => this is TState extends { value: TSV }
? TState & { value: TSV }
: never;
) => this is State<
(TState extends any
? { value: TSV; context: any } extends TState
? TState
: never
: never)['context'],
TEvent,
TState
> & { value: TSV };
}

export type AnyMachine = StateMachine.Machine<any, any, any>;
Expand All @@ -118,16 +128,20 @@ export namespace StateMachine {
export interface Config<
TContext extends object,
TEvent extends EventObject,
TState extends Typestate<TContext> = { value: any; context: TContext }
TState extends Typestate<TContext> = Typestate<TContext>
> {
id?: string;
initial: string;
initial: TState['value'];
context?: TContext;
states: {
[key in TState['value']]: {
on?: {
[K in TEvent['type']]?: SingleOrArray<
Transition<TContext, TEvent extends { type: K } ? TEvent : never>
Transition<
TContext,
TEvent extends { type: K } ? TEvent : never,
TState['value']
>
>;
};
exit?: SingleOrArray<Action<TContext, TEvent>>;
Expand Down Expand Up @@ -157,9 +171,7 @@ export namespace StateMachine {
TState extends Typestate<TContext> = { value: any; context: TContext }
> {
send: (event: TEvent | TEvent['type']) => void;
subscribe: (
listener: StateListener<State<TContext, TEvent, TState>>
) => {
subscribe: (listener: StateListener<State<TContext, TEvent, TState>>) => {
unsubscribe: () => void;
};
start: (
Expand Down
40 changes: 40 additions & 0 deletions packages/xstate-fsm/test/types.test.ts
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Expand Up @@ -18,4 +18,44 @@ describe('matches', () => {
((_accept: string) => {})(state.context.count);
}
});

it('should narrow context using typestates', () => {
type MyContext = { user: { name: string } | null; count: number };
type Typestates =
| {
value: 'idle';
context: { user: null; count: number };
}
| {
value: 'fetched';
context: { user: { name: string }; count: number };
};
const machine = createMachine<MyContext, { type: string }, Typestates>({
context: {
user: null,
count: 0
},
initial: 'idle',
states: { idle: {}, fetched: {} }
});
const state = machine.initialState;

if (state.matches('idle')) {
((_accept: null) => {})(state.context.user);
// @ts-expect-error
((_accept: { name: string }) => {})(state.context.user);

((_accept: number) => {})(state.context.count);
// @ts-expect-error
((_accept: string) => {})(state.context.count);
} else if (state.matches('fetched')) {
// @ts-expect-error
((_accept: null) => {})(state.context.user);
((_accept: { name: string }) => {})(state.context.user);

((_accept: number) => {})(state.context.count);
// @ts-expect-error
((_accept: string) => {})(state.context.count);
}
});
});