Unable to analyze next.config.js in a ESM package #762
Description
Bug Description
Next.js supports "type": "module" in package.json. When this property is set, next.config.js is treated as ESModule, so it needs to be import-edrather thanrequire-d. depcheck` does not take this into account and outputs an error:
Next.js webpack configuration detection failed with the following error Error [ERR_REQUIRE_ESM]: require() of ES Module /path/to/project/next.config.js from /path/to/.npm/_npx/ec702ce30756237c/node_modules/depcheck/dist/special/webpack.js not supported.
Instead change the require of next.config.js in /path/to/.npm/_npx/ec702ce30756237c/node_modules/depcheck/dist/special/webpack.js to a dynamic import() which is available in all CommonJS modules.
at loadNextWebpackConfig (/path/to/.npm/_npx/ec702ce30756237c/node_modules/depcheck/dist/special/webpack.js:153:24)
at parseWebpack (/path/to/.npm/_npx/ec702ce30756237c/node_modules/depcheck/dist/special/webpack.js:187:27)
at getDependencies (/path/to/.npm/_npx/ec702ce30756237c/node_modules/depcheck/dist/check.js:71:24)
at /path/to/.npm/_npx/ec702ce30756237c/node_modules/depcheck/dist/check.js:97:32
at Array.map (<anonymous>)
at checkFile (/path/to/.npm/_npx/ec702ce30756237c/node_modules/depcheck/dist/check.js:97:18)
at ReaddirpStream.<anonymous> (/path/to/.npm/_npx/ec702ce30756237c/node_modules/depcheck/dist/check.js:126:24)
at ReaddirpStream.emit (node:events:513:28)
at ReaddirpStream._read (/path/to/.npm/_npx/ec702ce30756237c/node_modules/readdirp/index.js:143:22) {
code: 'ERR_REQUIRE_ESM'
} Support for this feature is new and experimental, please report issues at https://github.com/depcheck/depcheck/issues
This should be fixable by replacing require with await import on this line:
depcheck/src/special/webpack.js
Line 166 in 5132d5e
As a result, loadNextWebpackConfig needs to become async. Replacing require should be backwards compatible because CommonJS modules can be import-ed (but not vice versa).
Code snippets
Discovered in https://github.com/blockprotocol/blockprotocol → apps/site
cd /tmp
git clone https://github.com/blockprotocol/blockprotocol.git
cd blockprotocol
yarn install
cd apps/site; npx depcheck@latest; cd -Versions
node -v:16.18.0npm -v:8.19.2npx depcheck@latest --version:1.4.3
Extra info
When looking into this issue, it might also worth adding support for next.config.mjs. This file can be used in projects that don’t define "type": "module" in package.json.