no-misused-generics: missing error for function value

[OliverJAsh]

I would expect an error here. Or is the lint rule not designed to catch this?

// error ✅
type Fn = <T>(param: T) => number;

// no error ❌
const fn = <T>(param: T) => 1;

[ajafff]

This is kinda working as intended. You could use the type parameter within the function body to ensure type safety or infer the return type:

function a<T>(param: T) {
  return param; // type parameter used in inferred return type
}

function b<T extends string>(param: Map<string, T>) {
  const v = param.get('foo')!;
  param.set('bar', v); // ok
  param.set('bar', 'v'); // should be an error, replacing the type parameter with its constraint makes this pass type checking
}

If you have a good idea how to handle such cases, especially the second case, I'm happy to change the rule.

[OliverJAsh]

Good point. It would probably be easy to check that the generic is not used as the return type, but it could be difficult to detect if the generic is used in the function body in some other way, such as in your Map example. 🤔