Avoid full reload in @tailwindcss/vite when editing a scanned file that is not a loaded module

[UditDewan]

Summary

Fixes #20320

In dev mode, @tailwindcss/vite's hotUpdate hook has a fallback that sends a full-reload for files that Tailwind scans but that aren't handled by Vite or any plugin (e.g. .php or .html templates). Without it, edits to those files wouldn't refresh the page at all.

However, the check ("every module for this file is an asset and/or has no id") also matches JS/TS source files that Tailwind has scanned but that Vite hasn't loaded as a module yet — lazy routes, unvisited chunks, and so on. The scanner's addWatchFile call creates an asset-type module-graph node with id === undefined for every scanned file, and for a not-yet-loaded .tsx there is no real JS node next to it, so the fallback fires and the whole page reloads, throwing away all client state. In apps with route-level code splitting this happens on almost every edit to a not-currently-loaded component.

This change exempts JS/TS module files (.js, .jsx, .ts, .tsx, .mjs, .cjs, .mts, .cts) from the fallback. Vite handles these files itself whenever they are actually loaded, and for scanned-but-unloaded files any new candidates still flow through the regular CSS update, so nothing is lost by skipping the reload:

• Editing a scanned-but-unloaded .ts file now results in a targeted {"type":"update"} for the Tailwind stylesheet instead of {"type":"full-reload"}, and the generated CSS includes the new candidates.
• Editing a scanned external .php file still triggers a full reload as before.

Test plan

• Added an integration test that boots a Vite 8 dev server with a src/unloaded.ts file that is scanned but never imported. A small fixture plugin wraps environment.hot.send to log every HMR payload. The test edits unloaded.ts and asserts that an update payload is sent (not a full-reload) and that the stylesheet regenerates with the new candidate.
• Verified both directions manually against a minimal reproduction (Vite 8.1.4): before the change, editing the unloaded file logs HOT_SEND {"type":"full-reload"}; after the change it logs HOT_SEND {"type":"update", ...} for /src/index.css and the CSS contains the new candidate. Editing a scanned .php file still logs HOT_SEND {"type":"full-reload"}.

pnpm exec vitest run --root=./integrations vite/index.test.ts -t "scanned module files that are not loaded do not trigger a full reload"

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 4e2c5e27-7811-44f2-8a6c-7ac58a75019f

📥 Commits

Reviewing files that changed from the base of the PR and between 35a3e9c and 70c4643.

📒 Files selected for processing (3)

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

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Walkthrough

The Vite plugin now detects external JavaScript and TypeScript files during hot updates and skips the full-reload path for them. A new integration test covers a scanned but unloaded module, captures HMR payloads, verifies an update instead of a full reload, and checks regenerated CSS. The changelog documents the fix under the unreleased changes.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main fix: avoiding full reloads for scanned files that are not yet loaded modules.
Description check	✅ Passed	The description matches the code changes and test coverage for the unloaded JS/TS hot-update behavior.
Linked Issues check	✅ Passed	The PR addresses #20320 by exempting scanned-but-unloaded JS/TS modules from the full-reload fallback while keeping template files on reload.
Out of Scope Changes check	✅ Passed	The changes stay focused on the hot-update fix, its integration test, and a changelog note with no unrelated additions.

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[greptile-apps]

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

_{Reviews (1): Last reviewed commit: "Add changelog entry" | Re-trigger Greptile}