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

• My proposal specifically checks TypeScript syntax, or it proposes a check that requires type information to be accurate.
• My proposal is not a "formatting rule"; meaning it does not just enforce how code is formatted (whitespace, brace placement, etc).
• I believe my proposal would be useful to the broader TypeScript community (meaning it is not a niche proposal).

Description

Validate that overriden method signatures match the base signature (i.e. no narrowing of types)

Fail Cases

class A {
  f(p: string | number) {
    console.log('A', p);
  }
}

class B extends A {
  f(p: string) {
    console.log('B', p, p.charCodeAt(0));
  }
}

const arrayOfA: Array<A> = [new A(), new B()];
for (const item of arrayOfA) {
  item.f(123);
}

Pass Cases

class A {
  f(p: string | number) {
    console.log('A', p);
  }
}

class B extends A {
  f(p: string | number) { <-- Needs to match base class method signature
    console.log('B', p, p.charCodeAt(0));
  }
}

const arrayOfA: Array<A> = [new A(), new B()];
for (const item of arrayOfA) {
  item.f(123);
}

Additional Info

TS issue was closed as "working as intended" but this is very dangerous, since this breaks some type safety, meaning that this introduces a risk of runtime errors