Show an error if there’s a file with no extension (#437)

This aims to help catch a common error: people adding a markdown file
for a post but forgetting to add the `.md` file extension.

If a file is found, the build will fail with an helpful error.

Author: frankieroberto

eleventy.config.js

@@ -1,7 +1,10 @@
 import fs from 'node:fs/promises'
+import path from 'node:path'
 
 import { nhsukEleventyPlugin } from '@x-govuk/nhsuk-eleventy-plugin'
 
+import { findFileWithoutExtension } from './lib/find-file-without-extension.js'
+
 const serviceName = 'Digital prevention services design history'
 
 export default function (eleventyConfig) {
@@ -174,6 +177,17 @@ export default function (eleventyConfig) {
 
   // Reset contents of output directory before each build
   eleventyConfig.on('eleventy.before', async ({ directories, runMode }) => {
+    // Check for files without extensions in the app directory
+    const fileWithoutExtension = await findFileWithoutExtension(
+      directories.input
+    )
+
+    if (fileWithoutExtension) {
+      throw new Error(
+        `Found file called '${path.basename(fileWithoutExtension)}' without an extension. Did you forget to add .md to it?\nFile path: ${fileWithoutExtension}`
+      )
+    }
+
     if (runMode === 'build') {
       await fs.rm(directories.output, {
         force: true,

lib/find-file-without-extension.js

@@ -0,0 +1,38 @@
+import fs from 'node:fs/promises'
+import path from 'node:path'
+
+/**
+ * Recursively find the first file without an extension in a directory
+ *
+ * @param {string} dir - Directory to search
+ * @returns {Promise<string|null>} - Path of first file without extension, or null
+ */
+export async function findFileWithoutExtension(dir) {
+  async function scan(currentDir) {
+    const entries = await fs.readdir(currentDir, { withFileTypes: true })
+
+    for (const entry of entries) {
+      const fullPath = path.join(currentDir, entry.name)
+
+      if (entry.isDirectory()) {
+        // Skip directories starting with underscore (e.g. _layouts, _components)
+        if (!entry.name.startsWith('_')) {
+          const found = await scan(fullPath)
+          if (found) return found
+        }
+      } else if (entry.isFile()) {
+        // Skip hidden files (e.g. .gitkeep)
+        if (!entry.name.startsWith('.')) {
+          // Check if the file has no extension
+          const ext = path.extname(entry.name)
+          if (ext === '') {
+            return fullPath
+          }
+        }
+      }
+    }
+    return null
+  }
+
+  return scan(dir)
+}