Add Avoid Conflicting Files as a Next.js TIL

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1434 TILs and counting..._
+_1435 TILs and counting..._
 
 ---
 
@@ -634,6 +634,7 @@ _1434 TILs and counting..._
 
 ### Next.js
 
+- [Avoid Conflicting Files](nextjs/avoid-conflicting-files.md)
 - [Create Files And Directories For Dynamic Routes](nextjs/create-files-and-directories-for-dynamic-routes.md)
 - [Define URL Redirects In The Next Config](nextjs/define-url-redirects-in-the-next-config.md)
 - [Fetch Does Not Work In API Serverless Function](nextjs/fetch-does-not-work-in-api-serverless-function.md)

nextjs/avoid-conflicting-files.md

@@ -0,0 +1,36 @@
+# Avoid Conflicting Files
+
+When Next.js is bundling and building your project, it will get completely
+tripped up by any instance of conflicting project files. What I mean by
+conflicting project files are two JavaScript or TypeScript (or flavors of JSX
+files) that would resolve to the same thing.
+
+Here is one example where the extensions differ:
+
+```
+src/pages/welcome.tsx
+src/pages/welcome.jsx
+```
+
+Here is another example where the paths differ but the bundled result would
+conflict:
+
+```
+src/pages/welcome.tsx
+src/pages/welcome/index.tsx
+```
+
+If you have any instances of these conflicting files, you'll be presented with
+a beguiling and cryptic error message when trying to run the dev server.
+
+```
+TypeError [ERR_INVALID_ARG_TYPE]: The "to" argument must be of type string. Received undefined
+    at new NodeError (node:internal/errors:405:5)
+    at validateString (node:internal/validators:162:11)
+    at Object.relative (node:path:1191:5)
+    at Watchpack.<anonymous> (/my_app/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected]/node_modules/next/dist/server/lib/router-utils/setup-dev-bundler.js:381:55) {
+  code: 'ERR_INVALID_ARG_TYPE'
+}
+```
+
+One of those files needs to go. Remove one of them and you'll be good to go.