refactor: 🏷️ stronger types for StateValue when using Typegen

[brunocrosier]

Demo of state.value having loose types while using Typegen: https://codesandbox.io/s/github/brunocrosier/test-xstate-typegen

Borrowing the type from: https://github.com/statelyai/xstate/blob/main/packages/core/src/State.ts#L321

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This pull request is automatically built and testable in CodeSandbox.

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[mattpocock]

lol @erikras just literally told me he wanted this when we went out for sushi

[brunocrosier]

lol @erikras just literally told me he wanted this when we went out for sushi

jealous! 🍣

I'm hoping this will work..!

[Andarist]

Shouldn't the TResolvedTypesMeta "flow" here from the outer type params? Right now I think that TResolvedTypesMeta should be the same across this whole class - but in here, we allow it to be different

[brunocrosier]

you're 100% correct - great catch! should be fixed here: b2a466f

[Andarist]

I think, but that would have to be verified, that reusing matchesStates is not good enough here because it accepts some object~ flavors that are not correct for the state.value.

q: why do you want to use state.value in the first place? I'm not saying that it's not OK - I just want to understand the context behind the request etc. I think that state.value & state.matches are so close to each other that I wonder if there is a value in having both of them in the API.

[brunocrosier]

I think, but that would have to be verified, that reusing matchesStates is not good enough here because it accepts some object~ flavors that are not correct for the state.value.

Sure thing! I could create a PR to add something like stateValues here: https://github.com/statelyai/xstate-tools/blob/e2d7a2b498fb4d3a666c434748d678ce6ca5f8e7/packages/shared/src/getTypegenOutput.ts#L164 ?

What would that look like though? How would it be different to matchesStates ?

q: why do you want to use state.value in the first place? I'm not saying that it's not OK - I just want to understand the context behind the request etc. I think that state.value & state.matches are so close to each other that I wonder if there is a value in having both of them in the API.

Basically, just for better type safety. I created a small repro here to show an example of when we get a type error when we should not: https://codesandbox.io/s/github/brunocrosier/test-xstate-typegen

Happy to explain in more detail if that's unclear!

[Andarist]

What would that look like though? How would it be different to matchesStates ?

One important difference is that only the "object syntax" is valid for state.value (+ string values for top-level atomic state) but a "dotted" notation is not valid:
https://github.com/statelyai/xstate-tools/blob/041846a873d58247fe17206f1e6149916203b449/packages/shared/src/getTypegenOutput.ts#L93-L97

Another one is that .matches always mark properties as optional:
https://github.com/statelyai/xstate-tools/blob/041846a873d58247fe17206f1e6149916203b449/packages/shared/src/getStateMatchesObjectSyntax.ts#L24
but for parallel regions in the .value this probably wouldn't be true, those should actually always be required.

[brunocrosier]

OK, I will see if I can create a PR in xstate-tools to add stateValues with the requirements that you mentioned 🙂

[Andarist]

It would still be pretty interesting to see some real-life examples of how you are using state.value in your code.

[brunocrosier]

It would still be pretty interesting to see some real-life examples of how you are using state.value in your code.

Unfortunately I don't have any examples apart from that minimal CodeSandbox, sorry! So far I've only played around with XState in personal projects - but I guess that stronger types are always better, right?

Maybe @erikras has some examples of potential use-cases?

Added PR here: statelyai/xstate-tools#160

[davidkpiano]

Superseded by #4498