Typesafety violation

[jacqueslenormand]

🔎 Search Terms

The following typechecks in version 5.8.3 (but shouldn't):

type Endpoints = {
  "/foo/bar": {
    output: {bar: boolean}
  },
  "/foo/bar2": {
    output: {bar2: boolean}
  },
}

function act<Path extends keyof Endpoints>(path: Path): Endpoints[Path]["output"] {
  if(path === "/foo/bar")  {
    return {bar2: true}
  }
  return {bar: false}  
}

const u : {bar: boolean} /* {bar:boolean} is incorrect */ = act("/foo/bar")
console.log(u) // {bar2: true}

🕗 Version & Regression Information

• This changed between versions ______ and _______
• This changed in commit or PR _______
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about version 5.8.3
• I was unable to test this on prior versions because _______

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/C4TwDgpgBAogdgEzAewJZ2AZygXigbwCgooAiAegDNllyAjAQwCdSAuA4kqZAV2DD7t8jJuzo0ANhAZwAvp1kAaThWq0RAJjYcu3PgOBDNYydLkLl8wpR5wAxsFTI4UShGB2AFgB4ACg2BPKAgAD2AIRGwAawgQZEpYRBR0LAA+AAowAM92f0CASnZ4JDQMTABtPM8AXXLSXn4+UmqdKFRKTOzcHDxVGnpmUnySIl0mdx4mF2FmDXZgJh4IeRIVqHHgSemRdkoGCUxlkkIrO2dMYCgeKCNmE2QpGVlcV3cvdL71QfzCM7hMB4QAB0EmQAHN0jx8kA

💻 Code

type Endpoints = {
  "/foo/bar": {
    output: {bar: boolean}
  },
  "/foo/bar2": {
    output: {bar2: boolean}
  },
}

function act<Path extends keyof Endpoints>(path: Path): Endpoints[Path]["output"] {
  if(path === "/foo/bar")  {
    return {bar2: true}
  }
  return {bar: false}  
}

const u : {bar: boolean} /* {bar:boolean} is incorrect */ = act("/foo/bar")
console.log(u) // {bar2: true}

🙁 Actual behavior

It typechecks, but shouldn't. act("/foo/bar") has the wrong type.

🙂 Expected behavior

I would have expected a type error

Additional information about the issue

No response

[RyanCavanaugh]

Duplicate #33014