Error when ctx.options.map is being used in postcss.config.js

[ikornienko]

• Operating System: macOS Catalina
• Node Version: 14.15.1
• NPM Version: 6.14.8
• webpack Version: 4.42.1
• postcss-loader Version: 4.0.4

Expected Behavior

No failure with the valid postcss.config.js.

Actual Behavior

Seeing an error

Module build failed (from ./node_modules/gatsby-plugin-postcss/node_modules/postcss-loader/dist/cjs.js):
TypeError: Cannot read property 'map' of undefined
    at Object.module.exports [as config] (project_dir/postcss.config.js:84:20)
    at loadConfig (project_dir/node_modules/gatsby-plugin-postcss/node_modules/postcss-loader/dist/utils.js:89:28)
    at async Object.loader (project_dir/node_modules/gatsby-plugin-postcss/node_modules/postcss-loader/dist/index.js:53:22)

Code

postcss.config.js (especially line 84 mentioned in the error) has a config

module.exports = (ctx) => ({
  map: ctx.options.map,  // this one is line 84
  plugins: [
    ...

It's a valid syntax as specified in postcss-cli docs, and postcss-cli works fine on it, only when this config is being loaded by postcss-loader in the context of gatsby-plugin-postcss then it fails.

Additional Context

It happens during the Gatsby build, when gatsby-plugin-postcss uses postcss-loader to read the config. I have NOT opened an issue with gatsby-plugin-postcss. The project is using gatsby-plugin-postcss version 3.1.0.

[ikornienko]

Not sure if it can be related to #480 because a different loader is now being used.

[alexander-akait]

It's a valid syntax as specified in postcss-cli docs, and postcss-cli works fine on it, only when this config is being loaded by postcss-loader in the context of gatsby-plugin-postcss then it fails.

We don't have compatibility with webpack-cli due it was abandoned a long time, I will try to fix it

[alexander-akait]

Also I think you need to open an issue in postcss-cli repo, because many things are really weird and I don't want to implement them here:

• https://github.com/postcss/postcss-cli/blob/master/index.js#L51 - overriding process.env.NODE_ENV is the very very very bad idea in vendor code, it is unsafe
• https://github.com/postcss/postcss-cli/blob/master/index.js#L176 - why? what if I need something more, for example name or root https://nodejs.org/api/path.html#path_path_parse_path, so we pass it as string
• https://github.com/postcss/postcss-cli/blob/master/index.js#L29 - why you need require something if the config file can override it, it reduces performance and it is weird
• https://github.com/postcss/postcss-cli/blob/master/index.js#L30 - default values is another

But I can pass postcssOptions from the loader to your config for keeping some compatibility

[ikornienko]

@evilebottnawi thank you for the response and a light speed fix + release! The concerns you bring about postcss-cli are indeed disturbing. I don't have all the context, TBH I haven't worked with postcss-cli too close. Just happened to be helping on a project that actively uses it, and on that project the attempt to upgrade gatsby-plugin-postcss broke the build because of the issue you just fixed :)

Thank you again for such an outstanding project maintenance discipline with this quick fix!