bug with merging cacheGroups

[alexander-akait]

Reproducible test repo: https://github.com/artem-malko/webpack-5-beta-config-bug

Ref: webpack/webpack#11396

Simple reproducible example

console.log(
  merge(
    { 
      optimization: {
        runtimeChunk: {
          name: 'runtime',
        },
    
        splitChunks: {
          minChunks: 2,
              minSize: 30000,
      
              cacheGroups: {
            clientApplication: {
              name: 'clientApplication',
                  test: /applications\/client/,
                  chunks: 'all',
                  enforce: true,
            },
          },
        },
      }
    },
    {
      optimization: {
        runtimeChunk: {
          name: 'runtime',
        },

        splitChunks: {
          minChunks: 2,
          minSize: 30000,

          cacheGroups: {
            clientApplication: {
              name: 'clientApplication',
              test: /applications\/client/,
              chunks: 'all',
              enforce: true,
            },
          },
        },
      }
    }
  ).optimization?.splitChunks
);

test is Object

[bebraw]

Thanks for the report. The problem was that there was a check missing against merging a RegExp against another RegExp. In this case in the configuration definition it was set up so that the optimization part was merged to itself optimization due to a ... elsewhere in the configuration.

@artem-malko I've fixed the issue in 5.1.3 but I would recommend against doing ...clientConfig.optimization, in your production configuration as that will cause the same configuration to appear twice although it will be merged away. Can you explain why you did your own merge for that particular configuration? What's the use case?

[artem-malko]

@bebraw Hm, nice catch) May be it's because where was no any webpack-merge many years ago) So, we merged our configs manually)

You're right! I'll remove ...clientConfig.optimization from my config) optimization part will be used without it too) Thx