feat: allows overriding import map location (#11532)

By default, Payload only attempts to locate the import map file in the following locations:

- `src/app/(payload)/{adminroute}/importMap.js`
- `app/(payload)/{adminroute}/importMap.js`

This is fine for most projects, but sometimes you may want to place the import map - or the Payload admin directory - somewhere else.

This PR adds a new `importMapFile` property that allows you to override this heuristic and specify your own import map path.

docs/custom-components/overview.mdx

@@ -119,10 +119,32 @@ For details on how to build Custom Components, see [Building Custom Components](
 
 ### Import Map
 
-In order for Payload to make use of [Component Paths](#component-paths), an "Import Map" is automatically generated at `app/(payload)/admin/importMap.js`. This file contains every Custom Component in your config, keyed to their respective paths. When Payload needs to lookup a component, it uses this file to find the correct import.
+In order for Payload to make use of [Component Paths](#component-paths), an "Import Map" is automatically generated at either `src/app/(payload)/admin/importMap.js` or `app/(payload)/admin/importMap.js`. This file contains every Custom Component in your config, keyed to their respective paths. When Payload needs to lookup a component, it uses this file to find the correct import.
 
 The Import Map is automatically regenerated at startup and whenever Hot Module Replacement (HMR) runs, or you can run `payload generate:importmap` to manually regenerate it.
 
+#### Overriding Import Map Location
+
+Using the `config.admin.importMap.importMapFile` property, you can override the location of the import map. This is useful if you want to place the import map in a different location, or if you want to use a custom file name.
+
+```ts
+import { buildConfig } from 'payload'
+import { fileURLToPath } from 'node:url'
+import path from 'path'
+const filename = fileURLToPath(import.meta.url)
+const dirname = path.dirname(filename)
+
+const config = buildConfig({
+  // ...
+  admin: {
+    importMap: {
+      baseDir: path.resolve(dirname, 'src'),
+      importMapFile: path.resolve(dirname, 'app', '(payload)', 'custom-import-map.js'), // highlight-line
+    },
+  },
+})
+```
+
 #### Custom Imports
 
 If needed, custom items can be appended onto the Import Map. This is mostly only relevant for plugin authors who need to add a custom import that is not referenced in a known location.
@@ -146,7 +168,7 @@ export default buildConfig({
       },
     },
   }
-}
+})
 ```
 
 ## Building Custom Components

packages/payload/src/bin/generateImportMap/index.ts

@@ -209,16 +209,29 @@ export async function writeImportMap({
   log?: boolean
   rootDir: string
 }) {
-  let importMapFolderPath = ''
-  if (fs.existsSync(path.resolve(rootDir, `app/(payload)${config.routes.admin}/`))) {
-    importMapFolderPath = path.resolve(rootDir, `app/(payload)${config.routes.admin}/`)
-  } else if (fs.existsSync(path.resolve(rootDir, `src/app/(payload)${config.routes.admin}/`))) {
-    importMapFolderPath = path.resolve(rootDir, `src/app/(payload)${config.routes.admin}/`)
+  let importMapFilePath: string | undefined = undefined
+
+  if (config?.admin?.importMap?.importMapFile?.length) {
+    if (!fs.existsSync(config.admin.importMap.importMapFile)) {
+      throw new Error(
+        `Could not find the import map file at ${config.admin.importMap.importMapFile}`,
+      )
+    }
+    importMapFilePath = config.admin.importMap.importMapFile
+  } else {
+    const appLocation = path.resolve(rootDir, `app/(payload)${config.routes.admin}/`)
+    const srcAppLocation = path.resolve(rootDir, `src/app/(payload)${config.routes.admin}/`)
+
+    if (fs.existsSync(appLocation)) {
+      importMapFilePath = path.resolve(appLocation, fileName)
+    } else if (fs.existsSync(srcAppLocation)) {
+      importMapFilePath = path.resolve(srcAppLocation, fileName)
     } else {
       throw new Error(
-      `Could not find the payload admin directory. Looked in ${path.resolve(rootDir, `app/(payload)${config.routes.admin}/`)} and ${path.resolve(rootDir, `src/app/(payload)${config.routes.admin}/`)}`,
+        `Could not find Payload import map folder. Looked in ${appLocation} and ${srcAppLocation}`,
       )
     }
+  }
 
   const imports: string[] = []
   for (const [identifier, { path, specifier }] of Object.entries(importMap)) {
@@ -237,8 +250,6 @@ ${mapKeys.join(',\n')}
 }
 `
 
-  const importMapFilePath = path.resolve(importMapFolderPath, fileName)
-
   if (!force) {
     // Read current import map and check in the IMPORTS if there are any new imports. If not, don't write the file.
     const currentImportMap = await fs.promises.readFile(importMapFilePath, 'utf-8')

packages/payload/src/config/types.ts

@@ -855,9 +855,9 @@ export type Config = {
        * @default true
        */
       autoGenerate?: boolean
-      /** The base directory for component paths starting with /.
-       *
-       * By default, this is process.cwd()
+      /**
+       * The base directory for component paths starting with /.
+       * @default process.cwd()
        **/
       baseDir?: string
       /**
@@ -873,6 +873,11 @@ export type Config = {
           imports: Imports
         }) => void
       >
+      /**
+       * If Payload cannot find the import map file location automatically,
+       * you can manually provide it here.
+       */
+      importMapFile?: string
     }
     livePreview?: {
       collections?: string[]