Bug report

Describe the bug

In CI environments, when initially trying to start the server after build, it errors out with the following error:

ERR Error: Cannot find module 'webpack'
ERR Require stack:
ERR - /home/vcap/deps/0/node_modules/mini-css-extract-plugin/dist/index.js
ERR - /home/vcap/deps/0/node_modules/mini-css-extract-plugin/dist/cjs.js
ERR - /home/vcap/deps/0/node_modules/@zeit/next-css/css-loader-config.js
ERR - /home/vcap/deps/0/node_modules/@zeit/next-sass/index.js
ERR - /home/vcap/app/next.config.js
ERR - /home/vcap/deps/0/node_modules/next/dist/next-server/server/config.js
ERR - /home/vcap/deps/0/node_modules/next/dist/next-server/server/next-server.js
ERR - /home/vcap/deps/0/node_modules/next/dist/server/next.js
ERR - /home/vcap/app/routes/next.js
ERR - /home/vcap/app/helpers/startServer.js
ERR - /home/vcap/app/server.js
ERR     at Function.Module._resolveFilename (internal/modules/cjs/loader.js:625:15)
ERR     at Function.Module._load (internal/modules/cjs/loader.js:527:27)
ERR     at Module.require (internal/modules/cjs/loader.js:683:19)
ERR     at require (internal/modules/cjs/helpers.js:16:16)
ERR     at Object.<anonymous> (/home/vcap/deps/0/node_modules/mini-css-extract-plugin/dist/index.js:7:16)
ERR     at Module._compile (internal/modules/cjs/loader.js:776:30)
ERR     at Object.Module._extensions..js (internal/modules/cjs/loader.js:787:10)
ERR     at Module.load (internal/modules/cjs/loader.js:643:32)
ERR     at Function.Module._load (internal/modules/cjs/loader.js:556:12)
ERR     at Module.require (internal/modules/cjs/loader.js:683:19) {
ERR   code: 'MODULE_NOT_FOUND',
ERR   requireStack: [
ERR     '/home/vcap/deps/0/node_modules/mini-css-extract-plugin/dist/index.js',
ERR     '/home/vcap/deps/0/node_modules/mini-css-extract-plugin/dist/cjs.js',
ERR     '/home/vcap/deps/0/node_modules/@zeit/next-css/css-loader-config.js',
ERR     '/home/vcap/deps/0/node_modules/@zeit/next-sass/index.js',
ERR     '/home/vcap/app/next.config.js',
ERR     '/home/vcap/deps/0/node_modules/next/dist/next-server/server/config.js',
ERR     '/home/vcap/deps/0/node_modules/next/dist/next-server/server/next-server.js',
ERR     '/home/vcap/deps/0/node_modules/next/dist/server/next.js',
ERR     '/home/vcap/app/routes/next.js',
ERR     '/home/vcap/app/helpers/startServer.js',
ERR     '/home/vcap/app/server.js'
ERR   ]
ERR }

It seems there is an issue with the mini-css-extract-plugin as part of @zeit/next-sass. We’ve been successfully using this plugin for over a year, with different versions of next.js from 6.0 up to 9.2, and a seemingly unrelated commit is now introducing this error that prevents the site from starting.

This was reported previously in the mini-css-extract-plugin repo: https://github.com/webpack-contrib/mini-css-extract-plugin/issues/198

To Reproduce

I know this isn’t helpful, but I’m unable to provide a repository at this time.

Expected behavior

The app should start.

Screenshots

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System information

• OS: Linux
• Version of Next.js: 9.2.2, “@zeit/next-sass”: “^1.0.1”,
• Version of Node.js: 12.6.0

Additional context

Add any other context about the problem here.