Callback was already called.

[gajus]

It appears that csso-webpack-plugin has some sort of concurrency condition:

/dev/node_modules/async/dist/async.js:955
        if (fn === null) throw new Error("Callback was already called.");
                         ^

Error: Callback was already called.
    at /dev/node_modules/async/dist/async.js:955:32
    at /dev/node_modules/csso-webpack-plugin/lib/index.js:185:32
    at /dev/node_modules/async/dist/async.js:3096:16
    at eachOfArrayLike (/dev/node_modules/async/dist/async.js:1055:9)
    at eachOf (/dev/node_modules/async/dist/async.js:1103:5)
    at Object.eachLimit (/dev/node_modules/async/dist/async.js:3158:5)
    at /dev/node_modules/csso-webpack-plugin/lib/index.js:118:37
    at /dev/node_modules/async/dist/async.js:3096:16
    at eachOfArrayLike (/dev/node_modules/async/dist/async.js:1055:9)
    at eachOf (/dev/node_modules/async/dist/async.js:1103:5)
    at Object.eachLimit (/dev/node_modules/async/dist/async.js:3158:5)
    at Compilation.<anonymous> (/dev/node_modules/csso-webpack-plugin/lib/index.js:117:33)
    at next (/dev/node_modules/tapable/lib/Tapable.js:204:14)
    at Compilation.<anonymous> (/dev/node_modules/babel-minify-webpack-plugin/dist/index.js:102:7)
    at next (/dev/node_modules/tapable/lib/Tapable.js:204:14)
    at Compilation.compilation.plugin (/dev/node_modules/babel-webpack-plugin/index.js:93:5)
    at Compilation.applyPluginsAsyncSeries (/dev/node_modules/tapable/lib/Tapable.js:206:13)
    at applyPluginsAsync.err (/dev/node_modules/webpack/lib/Compilation.js:663:10)
    at next (/dev/node_modules/tapable/lib/Tapable.js:202:11)
    at Compilation.<anonymous> (/dev/node_modules/extract-text-webpack-plugin/dist/index.js:275:11)
    at Compilation.applyPluginsAsyncSeries (/dev/node_modules/tapable/lib/Tapable.js:206:13)
    at applyPluginsAsyncSeries (/dev/node_modules/webpack/lib/Compilation.js:659:9)
    at next (/dev/node_modules/tapable/lib/Tapable.js:202:11)
    at /dev/node_modules/extract-text-webpack-plugin/dist/index.js:244:13
    at /dev/node_modules/async/dist/async.js:473:16
    at iteratorCallback (/dev/node_modules/async/dist/async.js:1050:13)
    at /dev/node_modules/async/dist/async.js:958:16
    at /dev/node_modules/extract-text-webpack-plugin/dist/index.js:227:15
    at /dev/node_modules/async/dist/async.js:473:16
    at eachOfArrayLike (/dev/node_modules/async/dist/async.js:1043:9)

It is a large project. I get this inconsistently. No clue what could trigger it.

The only configuration I have is:

new CssoWebpackPlugin({
    beforeCompress (ast, options) {
      options.usage = {
        scopes: getScopes(ast)
      };
    }
  })

Specifications

• CSSO Plugin version: v1.0.0-beta.12
• Webpack version: v3.11.0
• CSSO version: v3.5.0
• Node + npm versions: v9.8.0 and v5.6.0

/cc @zoobestik

[gajus]

I figured as much as that the callback is called multiple times.

The subject file to blame is manifest file, which is a file created using https://www.npmjs.com/package/webpack-assets-manifest.

[gajus]

The issue arrises when the callback throws an error,

csso-webpack-plugin/src/index.js

Line 79 in 9cf1e22

return callback();

In that case, the async is not completed and you arrive at:

csso-webpack-plugin/src/index.js

Line 144 in 9cf1e22

return callback();

The actual error is:

Error: original.line and original.column are not numbers -- you probably meant to omit the original mapping entirely and only map the generated position. If so, pass null for the original mapping instead of an object with empty or null values.

I have not figured out whether this is directly related to csso-webpack-plugin.

[gajus]

It looks like error is only triggered when I add babel-minify-webpack-plugin plugin. Somehow the latter messes up sourcemap mapping.

Here is a relevant issue.

webpack-contrib/babel-minify-webpack-plugin#68

Seems that csso-webpack-plugin is not to blame here.

However, csso-webpack-plugin logic needs to be fixed to prevent the callback being called twice. Otherwise the underlying error is masked.

[zoobestik]

async dropped from v2.0.0, let me know, if you will help problems with new versions.