Wrong unused variable with logical assigment

Bug Report

🔎 Search Terms

TS6133

🕗 Version & Regression Information

Version: 4.3.4 (nightly is also affected)

⏯ Playground Link

https://www.typescriptlang.org/play?noUnusedLocals=true&ts=4.3.4&strict=true#code/MYewdgzgLgBAZjAvDAFASiQPhgbwFAyEwA2AprAA4BOIAtgJYSkBcMACjQ0wDwCuYAazAgA7mGwAfGPwAmpOPTCkZSaWDkKlMgNwEiVcryphUGRNnxErManUakYAfkfIOdpgDoDEEMQBupOgeUAAWpGAo6Fg2nPaqsvKKymh6hAC+eGlAA

💻 Code

const f = () => {
    let promise: Promise<unknown> | undefined = undefined; // error: TS6133: 'promise' is declared but its value is never read.
    return () => {
        promise ??= Promise.resolve().then(() => promise = undefined)
    }
}

🙁 Actual behavior

error: TS6133: ‘promise’ is declared but its value is never read.

🙂 Expected behavior

Should be ok. Operator ??= reads variable (as well as ||= and other logical assignments)

[leonovalex]

I think ||= and &&= is also involved for same reason. Demo: (() => { let a = true; a ||= console.log('Executed')})() will not output ‘Executed’

[MartinJohns]

The variable is not actually read (aka used) anywhere. That the operators evaluate the content of the variable does not count as it being used.