Multiple versions of this library can't coexist

[Antonio-Laguna]

• Operating System (or Browser): macOS
• Node Version: 14.17.6
• postcss-values-parser Version: 6.0.1

How Do We Reproduce?

After this bug surfaced csstools/postcss-preset-env#225 we started to investigate what could be causing it given that it works locally but fails within postcss-preset-env@7.0.0

We've realised that registerWalker is modifying the prototype of Container which means that if you have multiple versions of this package running you're in for a bad time.

The registering happens here:

postcss-values-parser/lib/walker.js

Line 27 in 0357c82

Container.prototype[walkerName] = function walker(callback) {

which runs multiple times (once per version) while

postcss-values-parser/lib/walker.js

Line 43 in 0357c82

if ((isTypeCallable && node instanceof type) || (!isTypeCallable && node.type === type)) {

makes it so node is only an instance of type for the first postcss-values-parser that does it's registering which makes this non-deterministic and kind-of dangerous if multiple instances coexist.

Expected Behavior

Should be possible to have different versions without them interfering.

Actual Behavior

It's not possible to do that.

I understand that this is not a trivial change and I'm happy to contribute time and/or to discuss anything.

[shellscape]

I'd be happy to review a PR to resolve this. The package has been up and relatively stable for a number of years, so I don't have a lot of personal motivation to dive into this one.

[shellscape]

This is resolved in the major/css-tree branch, which will be released as v7