8$: Error on await () => {}

[strager]

Within async functions, await () => {} is invalid syntax, at least according to Node.js v15.5.1:

async function g() {
  f(await () => {});
}
g();

hello.js:2
  f(await () => {});
    ^^^^^^^

SyntaxError: Malformed arrow function parameter list

quick-lint-js reports no error for this code. Assuming that Node.js is standards-conforming, quick-lint-js should report an error for an attempted await for an arrow function.

[strager]

#278 is a related issue. #278 is about async()=>{} outside async functions. This task is about async()=>{} inside async functions. Perhaps the end result should be the same (i.e. same diagnostic and error recovery), but the parsing code seems to be different, so I thought they deserved separate tasks.

[keyehzy]

Will try this one, PR'ing soon.