noUncheckedIndexedAccess and checked bracket notation access

[PSeitz]

Bug Report

🔎 Search Terms

noUncheckedIndexedAccess bracket access undefined

🕗 Version & Regression Information

• I was unable to test this on prior versions because noUncheckedIndexedAccess is available since 4.1

⏯ Playground Link

// @noUncheckedIndexedAccess
const meObj: { [propName: string]: string } = {}
const meKey: keyof typeof meObj = 'meh'
if (meObj[meKey]){
  meObj[meKey].toString() // Object is possibly 'undefined'.
}

Workbench Repro

🙁 Actual behavior

Compile Error: Object is possibly 'undefined'. error

🙂 Expected behavior

Typescript should be able to recognize the existence of the property with a check. This generates a lot of wrong errors in our codebase when the noUncheckedIndexedAccess compiler flag is enabled.

[MartinJohns]

Duplicate of #10530. Type narrowing does not occur for indexed access forms e[k] where k is not a literal.

[PSeitz]

This one also has similar examples further below #41612
I'll close this one then.