setup().extend()

[davidkpiano]

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[Andarist]

extend can't be used to add event types, context types, etc. This should only support actions, actors, guards and delays

The problem is that this would become possible and incorrect:

setup({
  types: {} as { events: { type: 'FOO' } },
  actions: {
    doStuff: ({ event }) => {} // sees `{ type: 'FOO' }`
  }
}).extend({
  types: {} as { events: { type: 'BAR' } }, 
}).createMachine({
  initial: 'a',
  states: {
    a: {
      on: { BAR: 'b' }
    },
    b: {
      entry: 'doStuff' // oops, it got called with `{ type: 'BAR' }`
    }
  }
})

[davidkpiano]

Okay, that's fair

[Andarist]

setup({})
  .extend({
    actions: {
      doOneStuff: () => {},
    },
  })
  .createMachine({
    entry: "doOtherStuff", // this should be an error
  });

That's why I've mentioned on Discord that before doing this change we need to make it impossible to use non-implemented things when nothing was implemented in that "group".

[Andarist]

I have a draft for this change here but I didn't have time to finish it

[Andarist]

all those locations should be unions with their respective "outer" parameters, the same goes for guars and delays

[Andarist]

and in a similar manner, it's very likely that those nevers should be converted to their respective "outer" type parameters:

xstate/packages/core/src/setup.ts

Line 32 in 39702e6

? never

xstate/packages/core/src/setup.ts

Line 55 in 39702e6

? never

the defaults for those should still be never - the first call in a chain doesn't have any outer type parameters after all