Cannot index record with own key type

[Nixinova]

Bug Report

🔎 Search Terms

• error = Element implicitly has an 'any' type because expression of type X can't be used to index type 'Record<X, Y>'
• template literal tag type invalid in key

🕗 Version & Regression Information

• This is a crash
• This changed between versions 4.0.x and 4.1.x
• This is the behavior in every version I tried, and I reviewed the FAQ for entries
• I was unable to test this on prior versions

⏯ Playground Link

Playground link with relevant code

💻 Code

type Ver = `${string}.${string}`

const data: Record<Ver, string> = {
    '1.0': 'foo',
    '1.1': 'bar',
}

let ver: Ver = '1.0'
data[ver] // Error 7053

🙁 Actual behavior

Versions[ver] errors with Element implicitly has an 'any' type because expression of type '`${string}.${string}`' can't be used to index type 'Record<`${string}.${string}`, string>'. (??)

🙂 Expected behavior

TypeScript recognises that `${string}.${string}` === the key of Record<`${string}.${string}`,string>

[Nixinova]

Seems to be a duplicate of #40193 which in turn is marked as a duplicate of #37448 though I don't really understand the latter as the issue is philosophically worded.

Why doesn't my code work and how can I fix it? I'll close when that's answered.

[ahejlsberg]

Duplicate of #42192. Fixed in 4.4-beta and later.

[Nixinova]

Oh, okay, thanks.