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Turbopack Fails To Parse Named Scroll-State Container Queries Due To Outdated Lightningcss

Next.js build with Turbopack fails when encountering a named @container rule (e.g., @container scroll-content) that does not include a condition, because the bundled lightningcss version lacks support for named container queries (scroll-state). This causes 'Unexpected end of input' errors during CSS parsing, breaking builds for projects that rely on such CSS (e.g., nhsuk-frontend).

highConfidence 95%Next.js Affected V16.3.4

Origin Analysis

Turbopack's CSS parser uses an outdated version of lightningcss (pre v1.31.0) that does not support named container queries introduced in CSS Containment Module Level 3. The parser expects a condition after the container name, so when it encounters a bare name like `scroll-content`, it misinterprets the syntax and reaches an unexpected end of input. Lightningcss v1.31.0 added support for named scroll-state container queries, so upgrading to that version (or later) resolves the parse error.

1. Create a Next.js app with Turbopack (default). 2. Add a CSS file containing: `@supports (container-type: inline-size scroll-state) { @container scroll-content { .foo { max-width: 100cqw; } } }`. 3. Import the CSS in a page and run `next build`. Observe the build fails with 'Parsing CSS source code failed / Unexpected end of input'.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

Ensure that the lightningcss crate upgrade is thoroughly tested with existing CSS features used by Next.js applications. Check for any breaking changes in lightningcss v1.31.0 (unlikely for parsing). Validate with a variety of CSS files, including those with older container query syntax and preprocessor outputs. In case of regression, revert to previous version and disable scroll-state container query usage.