oxc-project / oxc-project/oxc-css-parser

A few invalid parse behavors found by css fuzzer

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Rust
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3h 11m
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Description

CSS Parser Fuzzer Cases

This repository collects minimized parser disagreement cases found by css-fuzzer.

Current verified parser versions:

  • postcss: 8.5.16
  • prettier CSS parser: prettier 3.9.4, __debug.parse(..., { parser: "css" })
  • lightningcss: 1.32.0
  • oxc-css-parser: 0.0.6 at oxc-project/oxc-css-parser@90911bd

Parser Symbols

✅ = clean parse. ❌ = not a clean parse: rejected, crashed, timed out, unsupported, or accepted with recoverable parser errors.

Only cases where oxc-css-parser is ❌ are listed below. OXC clean-accept cases stay under cases/ with full sidecar notes, but are not listed in this human triage table.

High Priority

ID Area Minimal case Why it matters oxc-css-parser postcss prettier CSS parser lightningcss Parser notes
ANCHOR-CONTAINER-001 Anchor Position 2 anchored query cases/high/at-rules/anchor-container-001-anchored-query.css CSS Anchor Position 2 includes @container anchored(fallback: ...); OXC rejects the condition even though parser-only tools accept the rule shape. ❌ ✅ ✅ ❌ OXC rejects: expect token ), but found <ident>. lightningcss rejects: Unexpected token Function("anchored").
LC-SCOPE-002 OXC rejects lightningcss-emitted empty @scope root cases/high/at-rules/lc-scope-002-empty-scope-roundtrip.css lightningcss accepts `@scope (.x a)and emits@scope (); oxc-css-parserrejects the emitted CSS withsimple selector is expected`, while postcss, Prettier, and lightningcss accept it. ❌ ✅ ✅
OXC-CONTAINER-001 Container query by name only cases/high/at-rules/oxc-container-001-name-only-query.css CSS Conditional 5 says a stylesheet can query for a container only by name; OXC rejects the name-only @container form while the other parsers accept it. ❌ ✅ ✅ ✅ OXC rejects: expect token <ident>, but found {.
OXC-SCROLL-001 Scroll-driven keyframe range selector cases/high/at-rules/oxc-scroll-001-keyframes-entry-range.css Scroll-driven animations allow timeline range names such as entry in keyframe selectors; OXC rejects entry 0% while the other parsers accept it. ❌ ✅ ✅ ✅ OXC rejects: expect token :, but found <percentage>.
OXC-SHADOW-PARTS-001 CSS Shadow Parts multi-ident ::part() cases/high/selectors/oxc-shadow-parts-001-multiple-part-ident.css CSS Shadow Parts allows multiple idents inside ::part(); OXC rejects the second ident while the other parsers accept the selector. ❌ ✅ ✅ ✅ OXC rejects: expect token ), but found <ident>.
OXC-COLOR-001 CSS Color 5 device-cmyk color profile cases/high/at-rules/oxc-color-001-device-cmyk-profile.css CSS Color 5 includes @color-profile and device-cmyk; OXC reports a recoverable parser error for the predefined profile name while the other parsers accept it cleanly. ❌ ✅ ✅ ✅ OXC accepts with recoverable error: dashed identifier is expected.

Medium Priority

ID Area Minimal case Why it matters oxc-css-parser postcss prettier CSS parser lightningcss Parser notes
DRAFT-TEMPLATE-001 CSS Template @page::slot() syntax cases/medium/at-rules/draft-template-001-page-slot-pseudo.css CSS Template Layout 1 includes @page::slot(g) examples; OXC rejects the pseudo syntax while parser-only tools accept it. ❌ ✅ ✅ ❌ OXC rejects: expect token ;, but found ::. lightningcss rejects: Unexpected token Colon.

Low Priority

ID Area Minimal case Why it matters oxc-css-parser postcss prettier CSS parser lightningcss Parser notes
STRICT-SEL-001 Invalid selector recovery cases/low/selectors/strict-sel-001-double-class-dot.css .a..b is invalid selector syntax. This is a recovery/leniency reference, not a likely strict-parser bug. ❌ ✅ ✅ ❌ OXC rejects: expect token <ident>, but found .. lightningcss rejects: Expected identifier in class selector, got Delim('.').
STRICT-VAR-001 Dynamic property name recovery cases/low/declarations/strict-var-001-dynamic-property-name.css CSS Values 5 shows that var() cannot be used as a property name and the declaration should be thrown away as a syntax error. ❌ ✅ ✅ ❌ OXC rejects: expect token :, but found (. lightningcss rejects: Unexpected token Semicolon.
STRICT-MQ-002 Invalid media query list recovery cases/low/media-queries/strict-mq-002-invalid-query-list-recovery.css Media Queries 5 says a grammar mismatch in one media query is replaced by not all; strict parsers reject this malformed-list example. ❌ ✅ ✅ ❌ OXC rejects: expect token <ident>, but found &. lightningcss rejects: Unexpected token Comma.
STRICT-MQ-003 Invalid media at-rule semicolon recovery cases/low/media-queries/strict-mq-003-invalid-media-semicolon.css @media test; is invalid media at-rule syntax. postcss and Prettier recover from the semicolon form, while strict parsers reject it. ❌ ✅ ✅ ❌ OXC rejects: expect token {, but found ;. lightningcss rejects: Unexpected token Semicolon.

Verification

Run the fuzzer verifier from a sibling css-fuzzer checkout after changing cases:

vp run verify-cases -- --dir ../css-parser-fuzzer-cases/cases --readme ../css-parser-fuzzer-cases/README.md --timeout-ms 1500 --check-minimized --minimize-attempts 80

The verifier checks sidecar note coverage, sidecar reproduction blocks, sidecar required headings with non-empty Spec Context or Triage Note explanatory text, sidecar title IDs for README-listed OXC issue cases, README coverage for every current OXC non-clean-accept case, stale links, unique case listing, case ID filename prefixes, High/Medium/Low priority grouping, priority folder consistency, complete human-readable README parser emoji rows with parser notes, complete sidecar parser matrix coverage, README emoji drift, sidecar parser matrix drift, continued parser disagreement, and whether the current structure-level reducer can still produce a shorter case with the same parser-result fingerprint. For recognized issue families, the reducer must preserve that family as well as the parser fingerprint.

Triage Rules

  • High priority: current or near-current CSS syntax where at least two parsers accept the input and one production parser rejects it, or any parser crashes or times out.
  • Medium priority: draft syntax with unclear implementation status, recovery-mode differences that may still affect formatter output, or parser-specific extensions.
  • Low priority: likely-invalid syntax, duplicate findings, or behavior that needs a stronger spec citation before escalation.

Refs:

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the listed minimized cases under cases/high, cases/medium, and cases/low, then compare their parser results and notes in README.md. Run the verifier from a sibling css-fuzzer checkout using the documented command; done means the relevant case metadata, parser behavior, and README remain consistent with the verifier checks.

Written by the indexing model from the issue text.

Assessment

Tech stack
css, rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Needs clarification
Newbie friendliness
45/100

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