feat: set meta.filename for modules loaded from disk

This provides an efficient heuristic for knowing if a module is virtual.

packages/vite/src/node/plugins/loadFallback.ts

@@ -9,12 +9,16 @@ export function loadFallbackPlugin(): Plugin {
   return {
     name: 'vite:load-fallback',
     async load(id) {
+      let filename: string
+      let code: string
       try {
-        // if we don't add `await` here, we couldn't catch the error in readFile
-        return await fs.readFile(cleanUrl(id), 'utf-8')
+        code = await fs.readFile((filename = cleanUrl(id)), 'utf-8')
       } catch (e) {
-        return fs.readFile(id, 'utf-8')
+        // Try unclean `id` to handle rare case where the file path
+        // contains the # character.
+        code = await fs.readFile((filename = id), 'utf-8')
       }
+      return { code, meta: { filename } }
     }
   }
 }

packages/vite/src/node/server/transformRequest.ts

@@ -155,6 +155,11 @@ async function doTransform(
   const mod = await moduleGraph.ensureEntryFromUrl(url)
   ensureWatchedFile(watcher, mod.file, root)
 
+  // add meta.filename if loaded from disk
+  if (loadResult == null) {
+    mod.meta = { ...mod.meta, filename: mod.file }
+  }
+
   // transform
   const transformStart = isDebug ? performance.now() : 0
   const transformResult = await pluginContainer.transform(code, id, {