Parser bug: top-level async and generator functions conflict with nested var declarations

[bakkot]

Another bug from fuzzing:

async function x() {}
{
  var x;
}

is improperly rejected. The same happens for function* and async function*, but not a plain function(){}, and not if the var x is at the top level of the program or function rather than nested inside of a block or loop header.

This also applies inside functions, as in

function outer() {
  async function x() {}
  {
    var x;
  }
}

Note that this would be the correct behavior at a higher level of nesting. It's only at the top level of programs and functions where function declarations are treated like var declarations for the purposes of determining conflicts.

The relevant part of the spec is TopLevelLexicallyDeclaredNames, which has a special case for HoistableDeclaration, which includes all four kinds of function declaration, not just non-async non-generator functions.

[evanw]

Thanks for the report!