Fix Dynamic Import Path Resolution for Internal Utils

Summary:
## Problem

*   Dynamic import of `./utils/fb/internal_utils` failed with 404 errors due to incorrect path resolution
*   `checkFbDirectoryExists()` returned `true` but subsequent import failed because of double `utils` in resolved URL

## Root Causes

1.  **Path Context Issue**: `safeImport.ts` in `utils/` directory resolved `./utils/fb/internal_utils` as `utils/utils/fb/internal_utils`
2.  **Detection Logic Issue**: Checked non-existent `fb/exists` file, got HTML fallback instead of actual file

## Changes Made
------------

### 1. Fixed `safeImport.ts`

`// Added path adjustment for utils/ context let adjustedPath = modulePath; if (modulePath.startsWith('./utils/')) {   adjustedPath = './' + modulePath.substring('./utils/'.length); }`

### 2. Fixed `**fbDetection.ts**`

```
// Check actual file instead of non-existent marker - const response = await fetch('./fb/exists', { method: 'HEAD' }); + const response = await fetch('./fb/internal_utils.ts', { method: 'HEAD' });  // Detect HTML fallback vs real file const contentType = response.headers.get('content-type') || ''; const isHtmlFallback = contentType.includes('text/html'); return response.ok && !isHtmlFallback;
```

Reviewed By: Sibylau

Differential Revision: D77977718

fbshipit-source-id: 8b017a0af417e8bdc27ddc997b665cdd928cb0a5

Author: FindHao

website/src/utils/fbDetection.ts

@@ -1,15 +1,22 @@
 /**
  * Utility to detect if the fb directory exists
- * This checks for the existence of the exists marker file in the fb directory
+ * This checks for the existence of the internal_utils file in the fb directory
  */
 
 export const checkFbDirectoryExists = async (): Promise<boolean> => {
   try {
-    // Try to fetch the exists marker file in the fb directory
-    const response = await fetch('/fb/exists', { method: 'HEAD' });
-    return response.ok;
+    // Try to fetch the actual internal_utils file in the fb directory
+    const response = await fetch('./fb/internal_utils.ts', { method: 'HEAD' });
+    
+    // Check if we got a successful response AND it's not HTML content
+    // Vite dev server returns 200 + HTML (index.html) for missing files as SPA fallback
+    const contentType = response.headers.get('content-type') || '';
+    const isHtmlFallback = contentType.includes('text/html');
+    
+    // Only consider it successful if we get 200 AND it's not HTML fallback
+    return response.ok && !isHtmlFallback;
   } catch (error) {
     // If the request fails, the directory likely doesn't exist
     return false;
   }
-}; 
+};

website/src/utils/safeImport.ts

@@ -1,21 +1,29 @@
 /**
  * Safe dynamic import utility that handles missing modules gracefully
- * This avoids build-time module resolution issues
+ * This avoids build-time module resolution issues for OSS/internal builds
  */
 
 /**
  * Safely imports a module by path, returning null if it doesn't exist
- * Uses Function constructor to avoid static analysis
+ * Uses string concatenation to bypass static analysis while maintaining proper path resolution
  */
 export async function safeImport(modulePath: string): Promise<any | null> {
   try {
-    // Use Function constructor to create dynamic import
-    // This completely bypasses static analysis
-    const dynamicImport = new Function('path', 'return import(path)');
-    const module = await dynamicImport(modulePath);
+    // Adjust path to account for safeImport.ts being in the utils directory
+    // When called from App.tsx with './utils/fb/internal_utils',
+    // we need to convert it to './fb/internal_utils' since we're already in utils/
+    let adjustedPath = modulePath;
+    if (modulePath.startsWith('./utils/')) {
+      adjustedPath = './' + modulePath.substring('./utils/'.length);
+    }
+
+    // Use string concatenation to create dynamic import path
+    // This bypasses static analysis while maintaining proper module resolution
+    const dynamicPath = '' + adjustedPath;
+    const module = await import(/* @vite-ignore */dynamicPath);
     return module;
   } catch (error) {
     console.warn(`Module ${modulePath} not available:`, error);
     return null;
   }
-} 
+}