[Bug] Undefined variable from lexical environment about esbuild HOT 2 CLOSED

Thanks for the report. This is something that I already know about and am working on fixing. It's my top priority. Unfortunately fixing it isn't straightforward because it requires a change to how scopes work.

The problem is caused by variables that are defined in a nested scope and then used in a sibling or parent scope. I have surprisingly not run in to this on all of the code bases I've tested so far. I only discovered it because of the library mentioned in #24.

This came up because I have a somewhat different way of doing scope analysis. I'm trying to keep the number of full-tree passes required to a minimum for speed, so I'm attempting to set up scopes and bind variables in the same pass. That mostly works except for this case.

I've already tried to fix this by doing a bottom-up algorithm instead of the top-down algorithm I'm currently using. It mostly works except that I'm also doing some AST transforms during the same pass that need to know if a given identifier is a specific global or not, which is information that isn't available at that point when using the bottom-up algorithm.

I think it should work without a performance penalty if I move scope construction from the binding pass to the parsing pass. That's what I plan to try next.

from esbuild.

So here is more simpler example:

var a = function () {
    var loop$1 = function () {
        console.log(name$1);
    };

    for (var name$1 in {c: 'c', d: 'd'}) loop$1();
};

a();

translates to

var a = function() {
    var loop$1 = function() {
        console.log(name$1);
    };
    for (var name$12 in {
        c: "c",
        d: "d"
    })
        loop$1();
};
a();

which produces the same error:

Uncaught ReferenceError: name$1 is not defined at loop$1

The same code bundled with browserify or just included without bundling produces no error.

from esbuild.