test: css addWatchFile in load hook

playground/hmr/__tests__/hmr.spec.ts

@@ -999,11 +999,20 @@ if (!isBuild) {
     await untilUpdated(() => el.evaluate((it) => `${it.clientHeight}`), '40')
   })
 
-  test('CSS HMR with this.addWatchFile', async () => {
+  test('CSS HMR with this.addWatchFile in transform hook', async () => {
     await page.goto(viteTestUrl + '/css-deps/index.html')
-    expect(await getColor('.css-deps')).toMatch('red')
-    editFile('css-deps/dep.js', (code) => code.replace(`red`, `green`))
-    await untilUpdated(() => getColor('.css-deps'), 'green')
+    expect(await getColor('.css-deps-transform')).toMatch('red')
+    editFile('css-deps/dep-transform.js', (code) =>
+      code.replace(`red`, `green`),
+    )
+    await untilUpdated(() => getColor('.css-deps-transform'), 'green')
+  })
+
+  test('CSS HMR with this.addWatchFile in load hook', async () => {
+    await page.goto(viteTestUrl + '/css-deps/index.html')
+    expect(await getColor('.css-deps-load')).toMatch('red')
+    editFile('css-deps/dep-load.js', (code) => code.replace(`red`, `green`))
+    await untilUpdated(() => getColor('.css-deps-load'), 'green')
   })
 
   test('hmr should happen after missing file is created', async () => {

playground/hmr/css-deps/dep-load.js

@@ -1,4 +1,4 @@
-// This file is depended by main.css via this.addWatchFile
+// This file is depended by main-load.css via this.addWatchFile
 export const color = 'red'
 
 // Self-accept so that updating this file would not trigger a page reload.

playground/hmr/css-deps/dep-transform.js

@@ -0,0 +1,8 @@
+// This file is depended by main-transform.css via this.addWatchFile
+export const color = 'red'
+
+// Self-accept so that updating this file would not trigger a page reload.
+// We only want to observe main.css updating itself.
+if (import.meta.hot) {
+  import.meta.hot.accept()
+}

playground/hmr/css-deps/index.html

@@ -1,8 +1,11 @@
-<div class="css-deps">should be red</div>
+<div class="css-deps-transform">should be red</div>
+<div class="css-deps-load">should be red</div>
 
 <script type="module">
-  import './main.css'
+  import './main-transform.css'
+  import 'virtual:css-deps-load.css'
   // Import dep.js so that not only the CSS depends on dep.js, as Vite will do
   // a full page reload if the only importers are CSS files.
-  import './dep.js'
+  import './dep-transform.js'
+  import './dep-load.js'
 </script>

playground/hmr/css-deps/main-transform.css

@@ -0,0 +1,3 @@
+.css-deps-transform {
+  color: replaced;
+}

playground/hmr/css-deps/main.css

@@ -1,3 +0,0 @@
-.css-deps {
-  color: replaced;
-}

playground/hmr/vite.config.ts

@@ -29,7 +29,8 @@ export default defineConfig({
     },
     virtualPlugin(),
     transformCountPlugin(),
-    watchCssDepsPlugin(),
+    watchCssDepsTransformPlugin(),
+    watchCssDepsLoadPlugin(),
   ],
 })
 
@@ -76,14 +77,15 @@ function transformCountPlugin(): Plugin {
   }
 }
 
-function watchCssDepsPlugin(): Plugin {
+// `addWatchFile` called from `transform` hook
+function watchCssDepsTransformPlugin(): Plugin {
   return {
-    name: 'watch-css-deps',
+    name: 'watch-css-deps-transform',
     async transform(code, id) {
       // replace the `replaced` identifier in the CSS file with the adjacent
       // `dep.js` file's `color` variable.
-      if (id.includes('css-deps/main.css')) {
-        const depPath = path.resolve(__dirname, './css-deps/dep.js')
+      if (id.includes('css-deps/main-transform.css')) {
+        const depPath = path.resolve(__dirname, './css-deps/dep-transform.js')
         const dep = await fs.readFile(depPath, 'utf-8')
         const color = dep.match(/color = '(.+?)'/)[1]
         this.addWatchFile(depPath)
@@ -92,3 +94,35 @@ function watchCssDepsPlugin(): Plugin {
     },
   }
 }
+
+// `addWatchFile` called from `load` hook
+function watchCssDepsLoadPlugin(): Plugin {
+  return {
+    name: 'watch-css-deps-load',
+    resolveId(id) {
+      if (id === 'virtual:css-deps-load.css') {
+        return '\0virtual:css-deps-load.css'
+      }
+    },
+    async load(id) {
+      if (id === '\0virtual:css-deps-load.css') {
+        const depPath = path.resolve(__dirname, './css-deps/dep.js')
+        this.addWatchFile(depPath)
+        return `\
+.css-deps-load {
+  color: replaced;
+}`
+      }
+    },
+    async transform(code, id) {
+      // replace the `replaced` identifier in the CSS file with the adjacent
+      // `dep.js` file's `color` variable.
+      if (id === '\0virtual:css-deps-load.css') {
+        const depPath = path.resolve(__dirname, './css-deps/dep-load.js')
+        const dep = await fs.readFile(depPath, 'utf-8')
+        const color = dep.match(/color = '(.+?)'/)[1]
+        return code.replace('replaced', color)
+      }
+    },
+  }
+}