webpack serve compiling twice with a specific dependency package.json

Bug report

What is the current behavior?

Webpack is compiling the project twice, when running in serve mode, if the project imports a library with the following package.json main config:

"main": "./lib/",

If the current behavior is a bug, please provide the steps to reproduce.

1. Open https://stackblitz.com/edit/webpack-double-compilation
2. Run npm start
3. Notice that compilation is run twice on start:

webpack 5.38.1 compiled successfully in 649 ms
...
webpack 5.38.1 compiled successfully in 54 ms

This will fix the problem:

1. Open webpack.config.js
2. Add the commented sdp-transform alias
3. Run npm start again
4. Notice that compilation is run once only:

webpack 5.38.1 compiled successfully in 588 ms 

You can also test this locally following this steps:

1. Install sdp-transform as a dependency
2. Import sdp-transform in an entry point
3. Run webpack serve
4. Notice that the compilation is now run twice

What is the expected behavior?

Compilation should only run once.

Other relevant information: webpack version: 5.38.1 and 5.37.1 Node.js version: v14.16.0 and v14.17.0 Operating System: stackblitz OS (?) and Windows 10 Additional tools: none

[david10sing]

I think I am experiencing the same issue with storybook webpack5 doing a build twice

[alexander-akait]

I think resolver try to watch something wrong, I do not look it deeply, but if you change "main": "./lib/index.js" (i.e. index.js) all works fine, anyway using "main": "./lib/" is working in commonjs Node.js, because by default we try to load index.js in directly, it is very intresting, because no RFC or something else about it, it s just side effect built-in Node.js commonjs loader