"Extracting CSS based on entry" example doesn't work

[pinkiebala]

• Operating System: ubuntu20.04
• Node Version: 12.16.1
• NPM Version: 6.13.4
• webpack Version: 4.36.1
• mini-css-extract-plugin Version: 1.1.0

Expected Behavior

Extracting CSS based on entry example should work.

In the reproduce repo,
CSS of comp1.css should merge into app1.css.
CSS of comp2.css should merge into app2.css.

Actual Behavior

Each of comp1 & comp2 has its own CSS chunk.

And:

function recursiveIssuer(m) {
  if (m.issuer) {
    return recursiveIssuer(m.issuer);
  } else if (m.name){ // <--- this is `undefined`
    return m.name;
  }
  return false;
}

How Do We Reproduce?

Here is the reproduce repo
https://github.com/pinkiebala/extract-css-entry-failed-reproduce

[cap-Bernardito]

There is an error in the documentation, we will fix it.

You can achieve the desired effect using the example below:

const webpackVersion = require("webpack").version;

function recursiveIssuer(m) {
  if (m.issuer) {
    return recursiveIssuer(m.issuer);
  }

  const chunks = webpackVersion === "4" ? m._chunks : m.getChunks();

  for (const chunk of chunks) {
    return chunk["name"];
  }

  return false;
}

module.exports = {
  entry: {
    app1: path.resolve(__dirname, "..", "src", "app1.js"),
    app2: path.resolve(__dirname, "..", "src", "app2.js"),
  },
  ...
  optimization: {
    splitChunks: {
      cacheGroups: {
        app1Styles: {
          // For webpack 4 name should not be equal entry. We recommend upgrading to webpack@5
          name: "style_app",
          test: (m, c, entry = "app1") =>
            m.constructor.name === "CssModule" && recursiveIssuer(m) === entry,
          chunks: "all",
          enforce: true,
        },
      },
    },
  },
};

[pinkiebala]

Thanks a lot!