Hoisting a var declaration past a lexical declaration of the same name should be a SyntaxError

[ianwjhalliday]

Second bullet point of block static semantics and similarly for function body static semantics.

E.g.

let x;
{
    var x; // error (already works)
    let y;
    var y; // should be an error (doesn't work)
    {
        var y; // should also be an error (doesn't work)
    }
}

This applies for var declarations hoisting past all lexical declarations, i.e. let, const, class, function (and generators and async functions).

[ianwjhalliday]

@bterlson if I am reading section B.3.3. correctly, it does not affect this rule. Is that correct? E.g. the following should be an error?

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

[ajklein]

@ianwjhalliday That case isn't an error because function declarations at the top level of a function are not lexical (see https://tc39.github.io/ecma262/#sec-function-definitions-static-semantics-vardeclarednames and https://tc39.github.io/ecma262/#sec-block-static-semantics-toplevelvardeclarednames)

[ianwjhalliday]

Tricky. Thanks, @ajklein!

[EdMaurer]

No breaking changes in 1.4 at this point.