Subpath imports don't work for built-in Node modules

[nex3]

Support for subpath imports was added in #293, but they're broken if one of the subpaths is a built-in Node.js module. To reproduce:

mkdir -p test/lib
cd test
npm init -f
npm i webpack webpack-cli

package.json:

{
    "name": "webpack-imports",
    "version": "1.0.0",
    "type": "module",
    "imports": {
        "#fs": {"node": "fs"}
    },
    "devDependencies": {
        "webpack": "^5.36.0",
        "webpack-cli": "^4.6.0"
    }
}

lib/main.js:

import '#fs';

Run npx webpack build --target node --entry ./lib/main.js. It produces this error:

assets by status 123 bytes [cached] 1 asset
./lib/main.js 14 bytes [built] [code generated]

WARNING in configuration
The 'mode' option has not been set, webpack will fallback to 'production' for this value.
Set 'mode' option to 'development' or 'production' to enable defaults for each environment.
You can also set it to 'none' to disable any default behavior. Learn more: https://webpack.js.org/configuration/mode/

ERROR in ./lib/main.js 1:0-13
Module not found: Error: Can't resolve '#fs' in '/tmp/test/lib'
resolve '#fs' in '/tmp/test/lib'
  using description file: /tmp/test/package.json (relative path: ./lib)
    resolve as internal import
      using imports field: fs
        Parsed request is a module
        using description file: /tmp/test/package.json (relative path: ./lib)
          resolve as module
            /tmp/test/lib/node_modules doesn't exist or is not a directory
            looking for modules in /tmp/test/node_modules
              single file module
                using description file: /tmp/test/package.json (relative path: ./node_modules/fs)
                  no extension
                    /tmp/test/node_modules/fs doesn't exist
                  .js
                    /tmp/test/node_modules/fs.js doesn't exist
                  .json
                    /tmp/test/node_modules/fs.json doesn't exist
                  .wasm
                    /tmp/test/node_modules/fs.wasm doesn't exist
              /tmp/test/node_modules/fs doesn't exist
            /tmp/node_modules doesn't exist or is not a directory
            /node_modules doesn't exist or is not a directory

webpack 5.54.0 compiled with 1 error and 1 warning in 168 ms

[vankop]

As a hack for now I could suggest to put ./fs.js in your app, where fs.js

module.exports = require('fs');

[sokra]

The workaround by @vankop sounds good. This is a little bit complicated to fix...

[nex3]

Does it? For non-subpath imports, Webpack already knows to avoid trying to bundle require('fs'). I'd assume that it could just re-use the same logic here.

[vankop]

@nex3 I have created small example, take a look https://github.com/vankop/bundle-fs

[alexander-akait]

Let's close in favor of #303

[nex3]

I don't think #303 addresses this—the core issue here is that this behavior is specified to work in Node.js, but Webpack is incompatible with it. In other words, this is a bug report, not a feature request that could be addressed by supporting the feature in some other way.

[alexander-akait]

It is the same, we don't support resolution built-in Node.js modules neither in imports nor in normal request, and we have never supported this here, so this is an improvement request for us