🔎 Search Terms

aliases lost

🕗 Version & Regression Information

Discussion with @Andarist:

• TypeFormatFlags.InTypeAlias is at fault here, it's rather hard to track its exact conceptual purpose. And it has been there forever - I found commits with it from 9 years ago
• I briefly thought this might be related to ur issue: Type alias printing regressed in TypeScript 4.2.2 #43031
  but now I'm pretty sure it isn't
• but it's also a somewhat funny issue because it complains about an alias for a union being lost and it was broken by a PR that... introduces improved union/intersection aliasing 😄 Preserve type aliases for union and intersection types #42149 , there was also a quick follow up to this PR that feels slightly related: Support re-aliasing of type alias instantiations #42284

Anyway, I'm sort of leaving breadcrumbs for myself - sorry for oversharing 😉 I'll dig further later

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/C4TwDgpgBAShDOBXANsAPAQQDRQKID4oBeKAbwCgoqoAnCAQwBMB7AO2RCgH1h6BzAFxQARAHkA1sMrU6TNhygA3eskQQhGcgF8oAHzLSqslu049+Q4QDF6AS2RTqtBiYUQaNZjSG5t5cowQAMbI9HRQQWzwwFC28HBIqEIAFIhCiKzirMwA7qwAlMSEiLHwsAgo6PSsIDjVIPj+kazRUABmrMRQmDgEybasYEIJlT14hPrRNAN8hUSEcSOo-YOFAPyxg1CWzJJAA

💻 Code

type Result<A, E> = { readonly _tag: "Ok" readonly value: A } | { readonly _tag: "Fail" readonly error: E } declare const isResult: (u: unknown) => u is Result<any, any> const fn = <A, E>(inp: Result<A, E> | string) => isResult(inp) ? inp : "ok"

🙁 Actual behavior

const fn: <A, E>(inp: Result<A, E> | string) => { readonly _tag: "Ok"; readonly value: A; } | { readonly _tag: "Fail"; readonly error: E; } | "ok"

🙂 Expected behavior

const fn: <A, E>(inp: Result<A, E> | string) => Result<A, E> | "ok"

Additional information about the issue

No response