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

[SychO9]

Summary

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

1. It ignores my tailwind.config.js's content and tries to go through every single file in the project.
2. 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

[coderabbitai]

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

• X
• Mastodon
• Reddit
• LinkedIn

_{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