Prevent @tailwindcss/vite crash under Vite's experimental bundledDev

[lazerg]

Summary

Under Vite's experimental bundledDev mode, the hotUpdate hook in @tailwindcss/vite gets called without a server. Vite only passes { type, file, modules } here, but the hook loops over Object.values(server.environments), so editing any file (JS, CSS, or HTML) throws TypeError: Cannot read properties of undefined (reading 'environments') and the dev server build fails.

The fix returns early when server is missing. Those environment loops only look at environments other than the current one, and the server-level hot/ws reload channels don't exist in this mode, so bailing out leaves the classic (non-bundledDev) dev path untouched.

Fixes #20378

Test plan

• Added a unit test that calls hotUpdate without a server and checks it doesn't throw. It fails on the current code and passes with the guard.
• Reproduced with a Vite 8 project using experimental.bundledDev: true: before the change, editing any JS/CSS/HTML file crashed the dev server; after it, edits work.
• pnpm run test and the @tailwindcss/vite integration suite both pass.

[ci-all]

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: f5fe27bb-22b9-4d58-a370-0d0002c0422c

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Reviewing files that changed from the base of the PR and between fdc4fa0 and b09bd43.

📒 Files selected for processing (1)

• integrations/vite/bundled-dev.test.ts

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Walkthrough

The Vite plugin now returns immediately when hotUpdate receives no server. A regression test verifies that the handler does not throw. An integration test covers initial and incremental CSS output, watched @source updates, and plugin errors in bundledDev mode. The changelog records the fix.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the primary fix for the @tailwindcss/vite crash under Vite's experimental bundledDev mode.
Description check	✅ Passed	The description directly explains the crash, the guard-based fix, affected mode, tests, and issue addressed.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

_{Reviews (4): Last reviewed commit: "check all chunks" | Re-trigger Greptile}

[coderabbitai]

Actionable comments posted: 1

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: f155b7b0-e0e7-4f94-b96b-240d78b5f3c0

📥 Commits

Reviewing files that changed from the base of the PR and between 276d1bb and fdc4fa0.

📒 Files selected for processing (3)

• integrations/vite/bundled-dev.test.ts
• packages/@tailwindcss-vite/src/index.test.ts
• packages/@tailwindcss-vite/src/index.ts

🚧 Files skipped from review as they are similar to previous changes (2)

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

[coderabbitai]

🩺 Stability & Availability | 🟡 Minor | ⚡ Quick win

Write each watched file before the retry loop.

retryAssertion reruns its callback after each failed assertion. Lines 109-119 and 129-134 therefore rewrite watched files on every retry. Each write can trigger another Vite rebuild. The test can keep observing a fallback or stale bundle and fail intermittently.

Move each fs.write call before its related retryAssertion call. The retry callback should only fetch and assert the rebuilt bundle.

Proposed change

-    await retryAssertion(async () => {
-      // Updates are additive and cause new candidates to be added.
-      await fs.write(
+    // Updates are additive and cause new candidates to be added.
+    await fs.write(
         'project-a/index.html',
         html`
           <head>
             <link rel="stylesheet" href="./src/index.css" />
           </head>
           <body>
             <div class="underline m-2">Hello, world!</div>
           </body>
         `,
-      )
-
+      )
+    await retryAssertion(async () => {
       let styles = await fetchBundledStyles()
       expect(styles).toContain(candidate`m-2`)
     })

The retry behavior is defined in integrations/utils.ts:663-679.

Also applies to: 127-141

[RobinMalfait]

Thanks!

Made a few small changes to make TypeScript happy.
Also added an integration test to verify that this mode also works, and not just not crashes.