Identities should report an error

🔍 Search Terms

Identity TS2367 impossible comparison

✅ Viability Checklist

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

Comparing identical literal (abc, 5, false) values in an "if" it should report it as redundant/impossible, similar to what TS2367 does.

📃 Motivating Example

https://www.typescriptlang.org/play?#code/FAMwrgdgxgLglgewgAhAhAKAlALlQQwBsBnAU2QG9hkbkAnUmMOlEIsgbmAF9hRJYiFACN8dbHgDk+SZWq0GTFskmSuvftHhJkMAIwYxAczyQA1hAQB3CFjm1kcEMgyp02ZAEIAvN910wcjsqeRoNBycXN0w7Xz8YAKC5UORw2kjXNBivXwISJJCHNJoM6I84vLJkYL4i2vTnV1FxOx8-SWFZGpTix0bkZvLcjq7kupTSwdbhmWqx2l7JsSH22e663iA

function foo(): false {
    return false;
}

function bar(): 'a' {
    return '';
}

function t1(arg: unknown) {
    if ( foo() !== true ) {

    }

    if ( foo() === true ) {

    }

    if ( foo() !== false ) {

    }

    if ( foo() === false ) {

    }

    if ( bar() !== 'b' ) {

    }

    if ( bar() === 'b' ) {

    }

    if ( bar() !== 'a' ) {

    }

    if ( bar() === 'a' ) {

    }
}

💻 Use Cases

1. What do you want to use this for?
   Get rid of legacy conditions/impossible code

2. What shortcomings exist with current approaches?
   No error reported

3. What workarounds are you using in the meantime?
   None, wasting time manually checking legacy code to see what can be removed.