@niksy this looks good. Please update your snapshots by merging from upstream/master and running npm run test -- --u. Once that's done I can merge this.

@shellscape OK, done, but now I got a lot of other updated files, is that OK?

Looks like you need to merge from upstream/master and reinstall dependencies because 0357c82 was merged before you updated your snapshots

@shellscape yup, forgot to install new dependencies, now it looks OK!

Fixing the hang is important. Capturing symbols as identifiers would break compatibility with CSS. Is there a way to fix the former without introducing the later?

@jonathantneal any chance you could concoct a test that would show the breakage that @niksy could work with to get an ideal solution?

I'm not sure if totally related (and I'm willing to open a separate issue if this is not related), but I've found that the parser also hangs indefinitely if this chunk of CSS is passed:

.leaflet-oldie .leaflet-popup-tip {
 filter: progid:DXImageTransform.Microsoft.Matrix(M11=0.70710678, M12=0.70710678, M21=-0.70710678, M22=0.70710678);
}

The previous CSS block was modified from here.

I've found this bug while trying to use postcss-env-function (which internally uses this library) while importing Leaflet CSS into a Next.js project. While debugging this error in an isolated environment (only with postcss-env-function and the chunk above), I noticed that this while loop never ends with the previous CSS chunk:

The script I used to test it was this one:

const postcss = require('postcss');
const postcssEnvFunction = require('postcss-env-function');
const plugins = [postcssEnvFunction()];
const css = `
.leaflet-oldie .leaflet-popup-tip {
 filter: progid:DXImageTransform.Microsoft.Matrix(M11=0.70710678, M12=0.70710678, M21=-0.70710678, M22=0.70710678);
}
`;
postcss(plugins)
 .process(css)
 .then(result => {
 console.log(result.css);
 });

This will also hang the parser (in the same while loop as before):

const { parse } = require('postcss-values-parser');
const css = 'progid:DXImageTransform.Microsoft.Matrix(M11=0.70710678, M12=0.70710678, M21=-0.70710678, M22=0.70710678)';
const ast = parse(css);
console.log(ast.toString());

As I said, I'm not sure if this issue is related to the one this PR tries to address. If it is not related, I can open another issue.

@jonathantneal checking back in on my last comment. Is that something you're able to do? If not, we can merge this as-is.

Patching Func#fromTokens or Func#test so that it does not swallow up the full stop (.) opens up other issues, therefore, I think you should merge this as-is.