[kevin9327]

What changed / motivation ?

The zero-dimensions value normalizer keeps the unit of a zero angle (0deg), time (0s), flex value (0fr) and percentage, and drops it for lengths. It compared the unit case-sensitively, but CSS units are ASCII case-insensitive, so the uppercase spellings fell through to the length branch and lost their unit:

stylex.create({
  x: { transitionDuration: '0MS' },        // .x…{transition-duration:0}           (invalid: a <time> needs a unit)
  y: { animationDelay: '0S' },             // .x…{animation-delay:0}               (invalid)
  w: { gridTemplateColumns: '0FR 1fr' },   // .x…{grid-template-columns:0 1fr}     (0px track, not a 0fr flex track)
});

transition-duration:0 is dropped by the browser, so the declaration silently does nothing, and 0 instead of 0fr changes the track sizing.

The fix lower-cases the unit before comparing. The uppercase spellings now compile to exactly the same CSS and class names as the lowercase ones (0s, 0deg, 0fr); nothing changes for lowercase input.

Linked PR/Issues

None. I found no open issue or PR about this. (Independent of #1999, which touches the timings normalizer.)

Additional Context

New test in packages/@stylexjs/babel-plugin/__tests__/transform-value-normalization-test.js: 0MS, 0S, 0DEG and 0FR 1fr compile to 0s, 0s, 0deg and 0fr 1fr. It fails on main (transition-duration:0) and passes with the fix. The other 20 tests in that file still pass.

I ran the babel-plugin suite from a sparse checkout with the published @stylexjs/stylex/@stylexjs/shared 0.19.1 instead of the workspace builds: 1010 passed, and the one failing test (legacy/stylex-transform-call-test.js) fails identically on main in that setup.

AI assistance: I used an AI coding assistant to help find and write this fix. I reviewed the change and ran the tests above myself.

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• Performed a self-review of my code

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[henryqdineen]

Nice optimizations!

Would transform: rotate(0DEG) be more accurate?