fix(upgrade): use v3 config content patterns when no @source is set by SychO9 · Pull Request #19779 · tailwindlabs/tailwindcss

SychO9 · 2026-03-10T14:57:32Z

Summary

Fixes two main problems I've come across on every project i try tp upgrade from v3 to v4:

It ignores my tailwind.config.js's content and tries to go through every single file in the project.
It wipes out files, and since it goes through every single file, it just wipes out all files.

When migrating from v3 to v4, the CSS entrypoint has no @source directive yet, leaving compiler.root as null. The fallback to '**/*' caused the tool to scan every file in the project (PHP migrations, config files, etc.) and unconditionally write them all back to disk.

Proposed solution:

Use the v3 JS config's content patterns (config.sources) as the scan scope when compiler.root is null, falling back to '**/*' only when no config sources are available
Skip fs.writeFile when the migrated content is identical to the original

This is likely a bug introduced from allowing the upgrade tool to also run on tailwind v4 projects.

8e826b1

@source

…skip writes when content is unchanged When migrating from v3 to v4, the CSS entrypoint has no @source directive yet, leaving compiler.root as null. The fallback to '**/*' caused the tool to scan every file in the project (PHP migrations, config files, etc.) and unconditionally write them all back to disk. - Use the v3 JS config's content patterns (config.sources) as the scan scope when compiler.root is null, falling back to '**/*' only when no config sources are available - Move config lookup before the sources IIFE to avoid a TDZ error - Skip fs.writeFile when the migrated content is identical to the original

coderabbitai · 2026-03-10T15:01:52Z

Walkthrough

This pull request modifies two files in the Tailwind CSS upgrade codemod package. The first change optimizes the template migration process by computing migrated content once and writing to the file only when the content differs from the original. The second change refactors configuration retrieval logic to fetch per-sheet configuration early and uses it to influence source file discovery during v3→v4 migrations. When compiler.root is null, the source discovery now respects per-sheet configuration sources instead of using a broad pattern scan, and removes a redundant configuration retrieval call.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: using v3 config content patterns when `@source` is not set, which directly addresses the core fix in the PR.
Description check	✅ Passed	The description is clearly related to the changeset, explaining the problems encountered, the proposed solutions, and how the changes address the issues of file scanning and unnecessary writes.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

Tip

Try Coding Plans. Let us write the prompt for your AI agent so you can ship faster (with fewer bugs).
Share your feedback on Discord.

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

coderabbitai

🧹 Nitpick comments (1)

packages/@tailwindcss-upgrade/src/index.ts (1)
305-314: Logic looks correct; minor type inconsistency in sources array.

The fallback logic correctly addresses the PR objective: when compiler.root is null during v3→v4 migration, the tool now uses the v3 config's content patterns instead of blindly scanning **/*.

However, there's a minor type inconsistency: config.sources (line 311) returns { base: string; pattern: string }[] without a negated property, while the fallback at line 313 and the regular case at line 317 add negated: false. This creates a mixed-type array when concatenated at line 318.

Since the downstream Scanner only reads base and pattern fields (per the Rust struct definition), this won't cause runtime issues, but you may want to normalize the shape for consistency.
♻️ Optional: Normalize source entries to consistent shape
          if (compiler.root === null) {
            if (config?.sources && config.sources.length > 0) {
-              return config.sources
+              return config.sources.map((s) => ({ ...s, negated: false }))
            }
            return [{ base, pattern: '**/*', negated: false }]
          }
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@packages/`@tailwindcss-upgrade/src/index.ts around lines 305 - 314, When
compiler.root is null the code returns config.sources which lacks the negated
field and later merges with entries that include negated: false; normalize the
shape by mapping each item in config.sources to include negated: false before
returning or concatenating so the array elements all share { base, pattern,
negated } shape; update the logic around compiler.root / config.sources in
packages/@tailwindcss-upgrade/src/index.ts (referencing compiler.root and
config.sources) to transform config.sources entries (e.g., via a .map) to add
negated: false.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@packages/`@tailwindcss-upgrade/src/index.ts:
- Around line 305-314: When compiler.root is null the code returns
config.sources which lacks the negated field and later merges with entries that
include negated: false; normalize the shape by mapping each item in
config.sources to include negated: false before returning or concatenating so
the array elements all share { base, pattern, negated } shape; update the logic
around compiler.root / config.sources in
packages/@tailwindcss-upgrade/src/index.ts (referencing compiler.root and
config.sources) to transform config.sources entries (e.g., via a .map) to add
negated: false.

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: efc768ee-1ff5-4e4a-b003-d447618b5678

📥 Commits

Reviewing files that changed from the base of the PR and between c586bd6 and df535b2.

📒 Files selected for processing (2)

packages/@tailwindcss-upgrade/src/codemods/template/migrate.ts
packages/@tailwindcss-upgrade/src/index.ts

This PR is an attempt to make the upgrade tooling more stable. ### TL;DR 1. When migrating from Tailwind CSS v3 → Tailwind CSS v4, only migrate files listed in the `config.content` instead of relying on v4's auto content detection feature 2. Skip writing files that have not been changed 3. Write changed files in a safe way: first write to a temporary file, then rename the file atomically 4. Never migrate files that are git ignored, even if they are listed in the `config.content` file 5. Always ignore `.env` and `.env.*` files when scanning for files. Most people will have this in their `.gitignore` file, but if not, then this is a fallback mechanism. --- Looking at the tailwindlabs#18972 issue, it looks like some people are running into weird situations where some of the contents is just gone. I have never been able to reproduce this on my own devices and in my own projects unfortunately. But there is definitely _something_ happening that's not right that people are running into. Therefore, this PR is an attempt to fix what I think _might_ be wrong, but I'm not 100% sure if these fixes are enough, or if something else is still happening here. This builds on top of the tailwindlabs#19779 PR which has some small fixes, but is incomplete to make this work. ### What's happening Looking at some of the comments, it looks like a few things are happening such as: 1. The upgrade tool is emptying out my files — it looks like these are only happening if you ctrl+c while the process is taking a while. It could be that a lot of files are being checked and therefore the tooling looks like its stuck. 6. The upgrade tool is looking at files it shouldn't look at — in Tailwind CSS v4 we have this concept of the auto-content detection. This means that we will look at any plain text file that is not git ignored. ### Fixes #### Emptying out files The files being emptied looks like it's because how `fs.writeFile` behaves by default. It opens the file handle with the `w` flag, which will first truncate the file before writing the new contents. This is not a single atomic operation, so a killed process in the middle will cause invalid state. When we migrate your template files, everything is happening in promises to migrate things at the same time. When a lot of files are being scanned, truncating might have happened already before we write the new content. Since we migrate a bunch of files in parallel, a ctrl+c could cause data loss in multiple files. To mitigate this, I switched to an alternative way of writing files. 1. First, we do some quick checks where if the contents didn't change we just bail out immediately. Files that don't include Tailwind CSS classes won't change, and therefore we don't need to override these files with the same contents. 2. When the migrated contents is empty, we bail out as well. I'm 100% sure that this is not the spot where the "emptying out" happens, I still believe it happens in the `writeFile` itself, but added it just in case. 7. Next, I introduced a safe write, where we first write to a temporary file in the same folder. We could write it to `/tmp`, but then we can't guarantee that we are on the same file system. If we ctrl+c at this stage, then the worst case scenario is that you have additional temporary files in your project, but your original files are still there. Once that file was written, we will use the atomic `fs.rename`. This should be atomic as long as we are on the same file system, so either the rename didn't happen yet, or it completed. I added an integration test for this, but I had to change the `writeFile` implementation slightly. In the test, we will truncate the file first, after that we will write the new contents. This is so that we have enough time to kill the current process and allows us to verify that we didn't clear out the file. Again, this is a hacky way of testing this, just because I can't reproduce this issue myself, let alone reproduce it reliable in a CI environment. Note: we are also using `realpath` to make sure that we are updating the real file. Otherwise, if we were dealing with a symlinked file, we would override the symlink with a "hard" copy instead. #### Touching files that should not be touched During the migration, we rely on the Tailwind CSS v4 auto detection logic which means that it will scan any plain text file that is not git ignored. Therefore changes to php files could happen because in theory they could contain Tailwind CSS classes. To solve this, when migrating from Tailwind CSS v3 to Tailwind CSS v4, we will _only_ take the sources into account that were listed in the `config.content` array. Since this was a requirement in Tailwind CSS v3, it should be safe to rely on this array. Additionally, this will make sure that we are dealing with way fewer files to migrate as well. On top of that, files that match the patterns in the content array that are git ignored will also be skipped. This is to prevent that we mutate files in `node_modules` for example. In one of the comments I read that `.env` files were emptied out. In most cases people will have these files gitignored but I explicitly added `.env` and `.env.*` as files to never ever touch by default when scanning. Last but not least, this also updates the output a little bit of the upgrade tool in case we skip content files (because of git ignore) and if we changed a file. <img width="1122" height="1376" alt="image" src="https://github.com/user-attachments/assets/318fdbbf-e319-4c7e-9648-ee9283842624" /> - "Git ignored folder, skipping: `./node_modules`": this is because the content array looks like this while the `node_modules` are being ignored: <img width="1090" height="398" alt="image" src="https://github.com/user-attachments/assets/7d694720-5671-47ec-bb2e-f24c5f2c4248" /> - "Migrated `./resources/views/vendor/filament-panels/components/logo.blade.php`": this is because **I** made a change to showcase this feature. Fixes: tailwindlabs#18972 Closes: tailwindlabs#19779 ### Test plan 1. Existing tests still pass 1. Added a dedicated integration test to ensure that we only take `config.content` into account when migrating from Tailwind CSS v3 to Tailwind CSS v4 projects. 1. Added a dedicated integration test to make sure that files listed in `config.content` that are also git ignored, will still be skipped. 1. Added a dedicated integration test to ensure that when `writeFile` is cancelled mid-write that our old files are still present. 1. Added a dedicated integration test to ensure that we ignore `.env` and `.env.*` files even if you didn't git ignore them. [ci-all] To verify on Windows --------- Co-authored-by: Sami <[email protected]>

SychO9 requested a review from a team as a code owner March 10, 2026 14:57

coderabbitai bot reviewed Mar 10, 2026

View reviewed changes

SychO9 mentioned this pull request Mar 21, 2026

v4 upgrader removing the content of all files in my project #18972

Closed

RobinMalfait mentioned this pull request Mar 24, 2026

Make upgrade tooling more stable #19846

Merged

RobinMalfait closed this in #19846 Mar 24, 2026

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

fix(upgrade): use v3 config content patterns when no @source is set#19779

fix(upgrade): use v3 config content patterns when no @source is set#19779
SychO9 wants to merge 1 commit intotailwindlabs:mainfrom
SychO9:fix/upgrade-scan-scope-and-skip-unchanged-writes

SychO9 commented Mar 10, 2026

Uh oh!

coderabbitai bot commented Mar 10, 2026

Uh oh!

coderabbitai bot left a comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

Uh oh!

Conversation

SychO9 commented Mar 10, 2026

Summary

Uh oh!

coderabbitai bot commented Mar 10, 2026

Walkthrough

Uh oh!

coderabbitai bot left a comment

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant