Vite: Don't crash with virtual module dependencies (#16780)

Fixes #16732

If we can not get the mtime from a file, chances are that the resource
is a virtual module. This is perfectly legit and we can fall back to
what we did before the changes in `4.0.8` (which is to rebuild the root
every time a change contains a dependency like that).

## Test plan

Added a test to mimic the setup from the repor in #16732. Also ensured
the repro now passes:

<img width="1278" alt="Screenshot 2025-02-24 at 17 29 38"
src="https://github.com/user-attachments/assets/d111273d-579f-44c2-82f5-aa32d6a1879a"
/>

Note that importing virtual modules directly in CSS does not work as the
resolver we use does not resolve against the Vite runtime it seems. This
is unrelated to the regression added in `4.0.8` though and something to
look into in the future.

CHANGELOG.md

@@ -13,6 +13,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - _Experimental_: Add `user-valid` and `user-invalid` variants ([#12370](https://github.com/tailwindlabs/tailwindcss/pull/12370))
 - _Experimental_: Add `wrap-anywhere`, `wrap-break-word`, and `wrap-normal` utilities ([#12128](https://github.com/tailwindlabs/tailwindcss/pull/12128))
 
+### Fixed
+
+- Vite: Don't crash when importing a virtual module in JavaScript that ends in `.css` ([#16780](https://github.com/tailwindlabs/tailwindcss/pull/16780))
+
 ## [4.0.8] - 2025-02-21
 
 ### Added

packages/@tailwindcss-vite/src/index.ts

@@ -202,8 +202,9 @@ class Root {
   private candidates: Set<string> = new Set<string>()
 
   // List of all build dependencies (e.g. imported  stylesheets or plugins) and
-  // their last modification timestamp
-  private buildDependencies = new Map<string, number>()
+  // their last modification timestamp. If no mtime can be found, we need to
+  // assume the file has always changed.
+  private buildDependencies = new Map<string, number | null>()
 
   constructor(
     private id: string,
@@ -334,14 +335,22 @@ class Root {
   }
 
   private async addBuildDependency(path: string) {
-    let stat = await fs.stat(path)
-    this.buildDependencies.set(path, stat.mtimeMs)
+    let mtime: number | null = null
+    try {
+      mtime = (await fs.stat(path)).mtimeMs
+    } catch {}
+    this.buildDependencies.set(path, mtime)
   }
 
   private async requiresBuild(): Promise<boolean> {
     for (let [path, mtime] of this.buildDependencies) {
-      let stat = await fs.stat(path)
-      if (stat.mtimeMs > mtime) {
+      if (mtime === null) return true
+      try {
+        let stat = await fs.stat(path)
+        if (stat.mtimeMs > mtime) {
+          return true
+        }
+      } catch {
         return true
       }
     }