Fix internal source map warnings

[RobinMalfait]

This PR fixes an internal source map warning when running tests. To solve this, we encode the = as \x3d instead. I'm not 100% sure if Vitest was hanging on this but it solved the following warning:

 ✓  @tailwindcss/cli  src/utils/format-ns.test.ts (21 tests) 3ms
11:43:59 AM [vite] (ssr) Failed to load source map for /Users/robin/github.com/tailwindlabs/tailwindcss/packages/@tailwindcss-node/dist/index.mjs.
Error: An error occurred while trying to read the map file at ${i}
Error: ENOENT: no such file or directory, open '/Users/robin/github.com/tailwindlabs/tailwindcss/packages/@tailwindcss-node/dist/${i}'
    at open (node:internal/fs/promises:634:25)
    at Object.readFile (node:internal/fs/promises:1238:14)
    at extractSourcemapFromFile (file:///Users/robin/github.com/tailwindlabs/tailwindcss/node_modules/.pnpm/vite@7.0.0_@types+node@20.19.1_jiti@2.6.1_lightningcss@1.31.1_patch_hash=tzyxy3asfxcqc7ihroou_7epcep7uhfc7zidzdmxzgvdzwi/node_modules/vite/dist/node/chunks/dep-Bsx9IwL8.js:8349:65)
    at loadAndTransform (file:///Users/robin/github.com/tailwindlabs/tailwindcss/node_modules/.pnpm/vite@7.0.0_@types+node@20.19.1_jiti@2.6.1_lightningcss@1.31.1_patch_hash=tzyxy3asfxcqc7ihroou_7epcep7uhfc7zidzdmxzgvdzwi/node_modules/vite/dist/node/chunks/dep-Bsx9IwL8.js:26405:22)

Test plan

1. Existing tests pass
2. Added a failing test to ensure that the source maps are emitted correctly

[coderabbitai]

Walkthrough

Adds a unit test for source map handling in the Tailwind CSS Node package that imports toSourceMap and asserts a minimal Source Map JSON yields a map and that map.comment('app.css.map') returns the expected CSS sourceMappingURL comment with a trailing newline. Also changes the generated comment to use an escaped equals sign (\x3d) in the sourceMappingURL token.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The pull request title clearly and concisely describes the main change: fixing internal source map warnings by encoding the equals sign.
Description check	✅ Passed	The description is directly related to the changeset, explaining the problem being solved, the solution implemented, and the test plan for verification.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

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

Inline comments:
In `@packages/`@tailwindcss-node/src/source-maps.test.ts:
- Around line 4-8: The test currently only checks map.comment('app.css.map')
which doesn't catch the regression in the actual emission logic; update the test
to assert on the emitted bundle/source text produced by toSourceMap (or the
function that concatenates map comments) instead of only map.comment, e.g. call
the emitter that returns the final CSS+sourceMappingURL string and assert it
does not contain an embedded file-level marker, or simulate the loader path that
previously triggered the Vite warning to reproduce the original failure;
reference to toSourceMap and map.comment and the emission logic in
source-maps.ts when locating the code to change.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 815216dc-48b5-4995-8e36-e1d6a65588cb

📥 Commits

Reviewing files that changed from the base of the PR and between ad9fdef and ae8de63.

📒 Files selected for processing (2)

• packages/@tailwindcss-node/src/source-maps.test.ts
• packages/@tailwindcss-node/src/source-maps.ts

[coderabbitai]

⚠️ Potential issue | 🟠 Major

This test doesn't actually guard the regression it names.

It only checks the runtime value of map.comment(). If Line 49 in packages/@tailwindcss-node/src/source-maps.ts is changed back to a literal =, this still returns the same string and the test keeps passing while the Vite warning can come back. Please assert on the emitted source text or reproduce the original loader failure instead.

Suggested test adjustment

+import { readFileSync } from 'node:fs'
 import { expect, it } from 'vitest'
 import { toSourceMap } from './source-maps'
 
 it('emits source map comments without embedding a file-level marker in the bundle source', () => {
   let map = toSourceMap('{"version":3,"sources":[],"names":[],"mappings":""}')
+  let source = readFileSync(new URL('./source-maps.ts', import.meta.url), 'utf8')
 
   expect(map.comment('app.css.map')).toBe('/*# sourceMappingURL=app.css.map */\n')
+  expect(source).toContain('sourceMappingURL\\x3d')
+  expect(source).not.toContain('sourceMappingURL=')
 })

🤖 Prompt for AI Agents

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

In `@packages/`@tailwindcss-node/src/source-maps.test.ts around lines 4 - 8, The
test currently only checks map.comment('app.css.map') which doesn't catch the
regression in the actual emission logic; update the test to assert on the
emitted bundle/source text produced by toSourceMap (or the function that
concatenates map comments) instead of only map.comment, e.g. call the emitter
that returns the final CSS+sourceMappingURL string and assert it does not
contain an embedded file-level marker, or simulate the loader path that
previously triggered the Vite warning to reproduce the original failure;
reference to toSourceMap and map.comment and the emission logic in
source-maps.ts when locating the code to change.

[coderabbitai]

🧹 Nitpick comments (1)

packages/@tailwindcss-node/src/source-maps.ts (1)

48-50: Consider adding a comment explaining the escape sequence.

The \x3d escape for = is a clever fix that prevents bundlers from incorrectly matching sourceMappingURL= in this source file. However, without context, future maintainers might be tempted to "simplify" this back to a literal =. A brief comment would preserve the intent.

📝 Suggested comment

   function comment(url: string) {
+    // Using \x3d instead of = to prevent bundlers from detecting this as a source map directive
     return `/*# sourceMappingURL\x3d${url} */\n`
   }

🤖 Prompt for AI Agents

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

In `@packages/`@tailwindcss-node/src/source-maps.ts around lines 48 - 50, The
function comment(url) uses the escape sequence \x3d instead of a literal '=' to
avoid bundlers or tools from matching "sourceMappingURL=" in this file; add a
brief inline comment above or beside the comment(url) function (or inside it)
explaining that \x3d is used intentionally to prevent bundlers from rewriting or
matching the sourceMappingURL token so future maintainers won't replace it with
'=' and break the bundling behavior.

🤖 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-node/src/source-maps.ts:
- Around line 48-50: The function comment(url) uses the escape sequence \x3d
instead of a literal '=' to avoid bundlers or tools from matching
"sourceMappingURL=" in this file; add a brief inline comment above or beside the
comment(url) function (or inside it) explaining that \x3d is used intentionally
to prevent bundlers from rewriting or matching the sourceMappingURL token so
future maintainers won't replace it with '=' and break the bundling behavior.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 929c5270-04b6-4bd0-a031-5621988b0dbb

📥 Commits

Reviewing files that changed from the base of the PR and between ae8de63 and 29c6978.

📒 Files selected for processing (2)

• packages/@tailwindcss-node/src/source-maps.test.ts
• packages/@tailwindcss-node/src/source-maps.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• packages/@tailwindcss-node/src/source-maps.test.ts