Before You File a Proposal Please Confirm You Have Done The Following...

• I have searched for related issues and found none that match my proposal.
• I have searched the current rule list and found no rules that match my proposal.
• I have read the FAQ and my problem is not listed.

My proposal is suitable for this project

• I believe my proposal would be useful to the broader TypeScript community (meaning it is not a niche proposal).

Link to the rule's documentation

https://typescript-eslint.io/rules/no-unnecessary-condition/

Description

Let's say:

function foo(): string | undefined {
  // bla bla bla
}
const bar = foo();
if (typeof bar === 'string') { // It's ok
  // bla bla bla
}

One day, I refactored the foo function to return string only:

function foo(): string {
  // bla bla bla
}
const bar = foo();
if (typeof bar === 'string') { // Smelly code. bar is always string. But no-unnecessary-condition does not report it
  // bla bla bla
}

Fail

const str:string = 'foo';
if (typeof str === 'string') {
  // bla bla bla
}

Pass

const str:string|undefined = 'foo';
if (typeof str === 'string') {
  // bla bla bla
}

Additional Info

No response