[eslint-plugin] Fix single-value background: foo shorthand silently dropped — add lint error with autofix

[alvinbillian]

Problem

Single-value background shorthand like this:

is compiled without any linter warnings but produced no background: red style, ommitting that style entirely, giving false-positive result. (Reproduction in StyleX Playground)

The compiler requires the longhand syntaxes, e.g. background-color: red or background-image: url(image.jpg) instead.

Multi-token values like background: 'red no-repeat' are already caught by the linter:

What changed in the fix

• The shorthand splitter already contains a full background token classifier that can identify colors, images, repeat keywords, attachment keywords, and position keywords. The fix routes single-token background values through this existing classifier instead of short-circuiting past it, so they are expanded to the correct longhand and flagged with an autofix.

• One special case:
  In CSS, global keywords (inherit, initial, unset, revert, revert-layer) on the background shorthand apply to all sub-properties simultaneously:

  

  There is no safe single-longhand expansion for this. Therefore, these are flagged as errors but with no autofix, leaving the developer to decide which specific longhands to set.

• Added test cases

Example cases

Before (silent failure):

After (lint error):

After (autofix applied):

Pre-flight checklist

• I have read the contributing guidelines
  Contribution Guidelines
• Performed a self-review of my code

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
stylex	Skipped		Jun 24, 2026 1:58am