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/prefer-nullish-coalescing/

Description

I propose that the rule should flag if statements that are equivalent to a nullish coalescing assignment (??=).

Fail

declare let foo: { a: string } | null;

declare function makeFoo(): { a: string };

function lazyInitializeByTruthiness() {
  if (!foo) {
    foo = makeFoo();
  }
}

function lazyInitializeByNullCheck() {
  if (foo == null) {
    foo = makeFoo();
  }
}

export { }

Pass

declare let foo: { a: string } | null;

declare function makeFoo(): { a: string };

function lazyInitializeByNullishCoalescingAssignment() {
  foo ??= makeFoo();
}

export { }

Additional Info

playground

relates to #6309