Next.js webpack configuration detection failed with the following error TypeError [ERR_INVALID_ARG_TYPE]: The "paths[0]" argument must be of type string. Received undefined

[jantimon]

Bug Description

Next.js Webpack Configuration Detection Fails in Depcheck

When using depcheck with a Next.js project, the detection of the webpack configuration fails. The error encountered is a TypeError [ERR_INVALID_ARG_TYPE], stating that the "paths[0]" argument must be of type string, but received undefined. This issue seems to stem from the way Next.js handles the .context of a webpack config, which is always a filepath. This mismatch in expectations causes depcheck to fail in processing the webpack configuration correctly.

Code Snippets

Where the dependency is used:

// next.config.js
const { withYak } = require("next-yak/withYak");

const nextConfig = {
  // your next.js config
};

module.exports = withYak(nextConfig);

Versions

• node -v: 20.9.0
• depcheck --version: 1.4.7

Possible fix:

I tried the following in our codebase and was able to fix the bug:

diff --git a/node_modules/depcheck/dist/special/webpack.js b/node_modules/depcheck/dist/special/webpack.js
index 7544ccc..76cb237 100644
--- a/node_modules/depcheck/dist/special/webpack.js
+++ b/node_modules/depcheck/dist/special/webpack.js
@@ -102,6 +102,7 @@ function parseWebpackConfig(webpackConfig, deps) {
 }
 async function loadNextWebpackConfig(filepath) {
   const fakeConfig = {
+    context: process.cwd(),
     plugins: [],
     module: {
       rules: []
@@ -119,7 +120,10 @@ async function loadNextWebpackConfig(filepath) {
     }
   };
   const fakeContext = {
-    webpack: _webpack.fakeWebpack,
+    webpack: {
+      context: process.cwd(),
+      ..._webpack.fakeWebpack
+    },
     defaultLoaders: {},
     dir: 'fakePath'
   };