feat: handle backslash in @utility name

[rozsazoltan]

Resolves #19607

Summary

I believe there is no obstacle to simply ignoring backslashes in the name. This way, various validators - which are not aware of Tailwind CSS's specific syntax (which allows the / character to be used directly in utility names) - can still be bypassed using backslashes. For example, instead of @utility push-1/2, one could use @utility push-1\/2, while the end result would be identical.

Test plan

I took a previous utility test as a baseline and extended it with backslashes, and I expect the same result in the output as in the original test case:

• https://github.com/rozsazoltan/tailwindcss/blob/main/packages/tailwindcss/src/utilities.test.ts#L28553-L28567 (the original test case I started from)
• https://github.com/rozsazoltan/tailwindcss/blob/feat/handle-blackslash-in-utility-name/packages/tailwindcss/src/index.test.ts#L4640-L4654 (the current PR's test)

[coderabbitai]

Walkthrough

Adds an unescape step when handling @utility so node.params with escaped characters (e.g., p\ush-1\/2, p\ush-50\%) are treated as their literal forms when creating utilities. Adds a test in the @utility suite that defines those escaped utilities and verifies the compiled CSS combines their selectors in one layer with the expected property (right: 50%).

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'feat: handle backslash in @utility name' accurately summarizes the main change: adding support for backslash-escaped characters in @utility names.
Description check	✅ Passed	The description is related to the changeset, explaining the problem (linters requiring escaped slashes), the solution (ignore backslashes), and linking to test cases demonstrating the fix.
Linked Issues check	✅ Passed	The PR fully addresses issue #19607 by implementing backslash handling in @utility names, allowing escaped utility names to produce identical output as unescaped forms, enabling compatibility with linters like Biome.
Out of Scope Changes check	✅ Passed	All changes are in-scope: modifications to index.ts add sanitization for escaped characters, and index.test.ts adds a test validating the backslash-handling behavior described in the linked issue.

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@packages/tailwindcss/src/index.ts`:
- Around line 234-235: The current blanket removal of backslashes (node.params =
node.params.replace(/\\/g, '')) breaks CSS hex/char escapes; replace that line
to call the existing unescape helper (e.g., node.params = unescape(node.params))
so CSS escapes like \61 are decoded correctly while still producing literal
characters for sequences such as \/ and \%; add the unescape import if missing
and ensure you reference the unescape helper when normalizing node.params.