Improve comparable relation of template literal types to detect more impossible situations

🔎 Search Terms

string condition always return false
2367 template

🕗 Version & Regression Information

This is the behavior in every version after 4.4.4 (including nightly), and I reviewed the FAQ for entries about "template" or "string"

This issue claims to fix a related problem in 4.5, but 4.5.5 is the first issue that fails for me. Maybe no relation though.
https://github.com/microsoft/TypeScript/issues/45201

In 4.4.4 it it fails correctly though, so maybe that fix is the regression of this issue?! https://www.typescriptlang.org/play?ts=4.4.4#code/C4TwDgpgBAglC8UAGBDAXGgJAbwHYFcBbAIwgCcBfJAKFEigCEFliMcCTyrrbxoANZkgAebPEVKUadaAE0h7CVxrUAxgHtcAZ2BR0sIeizYAjNw3bdrRkNbGzKizqiiogxCLEO1m5yDRQ8h443tQAlgBmUAAUwgjwiCAAlFDY1FBQTuoANhAAdNnqAObRAOTAABZhWlBaFer42QAmUBUoAG7QEShhuU2lSdQUPJExKPGIxClpGVm5BcVl3b01GmRkEKrA2SADQ9RAA

⏯ Playground Link

https://www.typescriptlang.org/play?#code/C4TwDgpgBAglC8UAGBDAXGgJAbwHYFcBbAIwgCcBfJAKFEigCEFliMcCTyrrbxoANZkgAebPEVKUadaAE0h7CVxrUAxgHtcAZ2BR0sIeizYAjNw3bdrRkNbGzKizqiiogxCLEO1m5yDRQ8h443tQAlgBmUAAUwgjwiCAAlFDY1FBQTuoANhAAdNnqAObRAOTAABZhWlBaFer42QAmUBUoAG7QEShhuU2lSdQUPJExKPGIxClpGVm5BcVl3b01GmRkEKrA2SADQ9RAA

💻 Code

type A = `a::${number}`
type B = `b::${number}`

type X = `x::${number}`
type Y = `${number}`

const a: A = `a::${1}`
const b: B = `b::${1}`

const x: X = `x::${1}`
const y: Y = `${1}`

if (x === y) {
  console.log('this should have failed')
}

if (a === b) {
  console.log('fails correctly')
}

🙁 Actual behavior

Comparing x and y generates no complaints from TS for "x::1" and "1", but does for "a::1" and "b::1". There is no way for a number to evaluate to "x:: so there is no overlap between these template types.

🙂 Expected behavior

I would expect that Typescript shows that error consistently whenever types don't match.

There is no overlap between a string that must start with "x::" and one that must start with a number.

Additional information about the issue

No response

Inizia riproducendo il confronto nel TypeScript Playground collegato e leggi l’issue correlata 45201 per il contesto. Traccia il modo in cui il verificatore dei tipi confronta i tipi literal di template; il lavoro è completato quando segnala la diagnostica no-overlap mancante per x e y senza introdurre regressioni nel comportamento esistente di a e b.