minimizerOptions fails when not serializable (using import/require)

[slorber]

• Operating System: macos
• Node Version: 14.16
• NPM Version: 6
• webpack Version: 5.28.0
• css-minimizer-webpack-plugin Version: 2.0.0

Expected Behavior

Using cssnano preset with a require call instead of a string preset + options object:

      new CssMinimizerPlugin({
        minimizerOptions: [
          // CssNano options
          {
            preset: require('cssnano-preset-advanced'), 
          },
        ],
        minify: [
          CssMinimizerPlugin.cssnanoMinify,
        ],
      })

Actual Behavior

ReferenceError: defaultOpts is not defined

Also tried with preset: require('cssnano-preset-advanced')(opts) (looks like the correct way to me) and got another similar error:

ReferenceError: _commentRemover is not defined

Code

cf above

How Do We Reproduce?

cf above

---

For context, Docusaurus is migrating to Webpack 5 (@alexander-akait helped review a bit our PR facebook/docusaurus#4089)

We have a custom CSSNano preset with some custom config + an additional postcss plugin: https://github.com/facebook/docusaurus/tree/master/packages/docusaurus-cssnano-preset

It's not 100% clear to me how I am supposed to provide our custom Cssnano preset to the CssMinimizer, as it seems there's some evaluation of options that prevent imports/requires in our preset. Do you have an example to share?

I believe that it is a similar issue that @RDIL already reported here: #58

[slorber]

Actually, this seems to work:

{
  preset: require.resolve('@docusaurus/cssnano-preset'),
}

Still think that what I tried should work.
But maybe just documenting this better or throwing a user-friendly error could be good enough?

[alexander-akait]

But maybe just documenting this better or throwing a user-friendly error could be good enough?

Yep, here problems with multi threading, we need serialize options and require is broken in this case, so we should use string here (i.e. require.resolve)

[alexander-akait]

@slorber Can you look at #84?