Inference of builder function fails when function parameter is included

[mskelton]

🔎 Search Terms

function parameter inference

🕗 Version & Regression Information

• This changed between versions 3.7.5 and 3.8.3

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/C4TwDgpgBA8mwEsD2A7AzgHgCoGFXAgA9gA+KAXigG8BYAKCilQGVgBDAJ2AH4AuKABQBKCmVz4iweo1QBRFABM+ggMYTi-cSgLER5MgDckCBfQC+9egDMArihWJUUFRwhsC2PNskkBAIxsEABsFCA5+AU4Ac34-JCQgtxQ9MjhHdE91UhFaBihXYBsOFCgA4NCOAWAOGwghc0s6AHomqAB1JA4AazR6FzcCAUiOGNL4xLZk0UFcmRRWTmAIlJmoRABbCH4UCAB3KAARdwhhKDMhABppJhR5BQi1b11p2cZnVDQEiAA6IKQogSPHTAb4bOrXMxXOjnep0egtdqdHp9VzHIYrASvFjsLjLaaYtYITbbPaHNEic5QuZ3B5ZFavRiPT6JX7-QFZUFE8F5SHmISw+GtABibGCaAAhCiBidhlEMVj5jiloJ5YTiVAdvsjoMKZdrnJFLSnsB6ddGR8vqyAUDJJzNiIEbIOBxOvwAOQ24huqAINBMKxrcDQN12LooJC7FBuiFQmH0IA

💻 Code

type Options<TContext> = {
  onStart?: () => TContext
  onEnd?: (context: TContext) => void
}

function create<TContext>(builder: (arg: boolean) => Options<TContext>) {
  return builder(true)
}

// Works
create((arg: boolean) => ({
  onStart: () => ({ time: new Date() }),
  onEnd: (context) => console.log(context.time)
}))

// Works
create(() => ({
  onStart: () => ({ time: new Date() }),
  onEnd: (context) => console.log(context.time)
}))

// Fails!
create((arg) => ({
  onStart: () => ({ time: new Date() }),
  onEnd: (context) => console.log(context.time) // Error: 'context' is of type 'unknown'
}))

🙁 Actual behavior

The value of TContext is not inferred properly when an parameter is included in the builder function. Removing the argument resolves the issue, as does adding an explicit type for the argument.

🙂 Expected behavior

The value of TContext should be inferred properly, regardless of if a parameter is included in the builder function, or if the parameter has or does not have an explicit type.

Additional information about the issue

No response

[Andarist]

I think this is a duplicate of this closed issue: #57021 . I have an experimental branch lying around somewhere that could address - I'll try to revamp it and push out soon-ish

[RyanCavanaugh]

See #47599

[mskelton]

Will close as duplicate and I'll follow those other issues. Thanks

[Andarist]

an experimental PR to fix this: #60909