Add support for @source inline and not inline syntax

[Copilot]

This PR adds support for Tailwind 4's @source inline and @source not inline syntax, which was previously causing validation errors in ESLint CSS rules.

Problem

The @source at-rule was defined with a too-restrictive prelude pattern of <string>, which only allowed simple string literals. This caused validation failures for the new Tailwind 4 syntax:

@source inline("{hover:,focus:,}underline");
@source not inline('container');

These would produce errors like:

Invalid prelude 'inline("{hover:,focus:,}underline")' found for at-rule '@source'. Expected '<string>'

Solution

Updated the @source prelude definition in tailwind4.js to support the official Tailwind CSS 4 syntax patterns:

1. Inline syntax: @source inline("class1", "class2") - for safelisting specific utilities
2. Not inline syntax: @source not inline("class") - for explicitly excluding classes

The new prelude pattern is: inline( <string># ) | not inline( <string># )

Changes

• Updated @source prelude definition in src/tailwind4.js
• Added comprehensive test cases covering all supported patterns
• Added validation tests to ensure proper lexer validation
• All existing functionality remains unchanged

Verification

The implementation correctly handles:

• ✅ @source inline("{hover:,focus:,}underline")
• ✅ @source inline("class1", "class2", "class3")
• ✅ @source not inline('container')

Edge cases are properly validated:

• Empty functions are rejected (e.g., @source inline())
• Invalid syntax like double negation is rejected
• Strings with spaces and special characters are supported

Fixes #18.

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[nzakas]

Double-check: Can url() be used with @source? I couldn't find that in the docs.

[nzakas]

@copilot double-check this please.

[Copilot]

You're absolutely right - url() is not supported with @source in Tailwind CSS 4. I incorrectly added that syntax. The @source directive is specifically for safelisting utilities and only supports inline() and not inline() functions. I've removed the URL support in commit 95547d4.