Fix measure-func leaf bug

[sedrew]

I use my own text layout engine for rendering. When a measure-function leaf has an explicit cross-axis size (e.g. width="30%" in a column or height="30%" in a row), Flexily should resolve that size and pass the resolved value to the measure function so the text is measured under the correct constraint. Instead, it was passing the parent's available cross-axis size, causing the text to be measured as if it had the parent's full width. As a result, text didn't wrap correctly and the measured height could incorrectly remain 1.

Root cause

In layout-zero.ts Phase 8 (passWidthToChild), measure-function leaves always received availCross as their cross-axis constraint, even when they had an explicit point, percent, cqi, cqmin, or calc() cross-axis size. The child's own cross-axis dimension was never resolved before calling the measure function.

Fix

Resolve the measure leaf's own cross-axis size before invoking the measure function:

• point → use the absolute value.
• percent → resolve against the parent's cross-axis size.
• cqi, cqmin, and calc() → resolve via resolveValue().

Pass this resolved value to cachedMeasure() instead of the parent's availCross.

Additionally, if flexGrow changes a row measure leaf's width, re-measure it after flex distribution using the final flex-distributed width so text wrapping and the resulting height reflect the actual width.

Test coverage

Four test cases cover the fix:

1. Row: flexGrow changes the leaf width → the leaf is re-measured at the final width and wrapping is updated.
2. Column: width="30%" resolves to 30px in a 100px parent instead of measuring at the parent's full width.
3. Cross-axis sizing: explicit point, percent, cqi, cqmin, and calc() values are correctly resolved before measurement.
4. Nested flex containers: percentage cross-axis sizes resolve correctly through intermediate flex containers.

All tests fail without the fix and pass with it.

Bug

because take parent width

Fix

[neftaly]

Hi! The description (and test header) say the fix is hasMeasureLeaf ? mainSizeToPass in passWidthToChild, but that's not in the diff? There's a re-measure instead.

[sedrew]

Thanks neftaly. In my first fix I tried to change like this. But after that I decided change the availCross. I have corrected my PR and commit title.

const passWidthToChild =
  isRow && mainIsAutoChild && !flexGrowHasDefiniteMainBudget && !flexDistChanged && !hasMeasureLeaf
    ? NaN
  : hasMeasureLeaf                                 // ← new hasMeasureLeaf
    ? mainSizeToPass                               // ← measure: childWidth 30% 
  : !isRow && crossIsAutoForLayoutCall && !parentHasDefiniteCross && !crossIsFitContent
    ? NaN
  : isRow && mainIsPercentForLayoutCall
    ? mainAxisSize
  : !isRow && crossIsPercentForLayoutCall
    ? crossAxisSize
  : !isRow && crossIsFitContent
    ? crossAxisSize
  : isRow
    ? mainSizeToPass
  : childWidth

[neftaly]

My LLM still has problems with this (I basically just started a fresh prompt with "Review #2, tell me what the comment should be, be consise").

Can you please make a commit that is just a failing fuzzer, and a few tests (1-3, 1-2 of them failing)? And no changes to the actual codebase.
Once we have some failing tests we can fix the root cause.

[sedrew]

At first I thought the bug was with width the measure function gets _w=100 (parent width) instead of _w=30 (30%). But logs showed that width is correct (_w=30). I think the problem is that height=1 from Phase 5 (pre-measure with _w=100) overwrites height=35 from Phase 4 (final size with _w=30), even though the measure function returns correct values in both phases. It showed in the first picture PR and below debug results. My LLM have wrote fix yoga-comparison is done but others tests fall. I glad continue to discussion it.

Bellow the summery

1. Collected debug data from yoga-comparison.test.ts

• I ran all 50 tests that compare Flexily with Yoga
• Found 6 failing tests in the MeasureFuncPercent group

2. Created tests/measure-percent.test.ts (new file)

• 6 tests that check only Flexily (no Yoga needed)
• They use expected values from Yoga as reference
• They catch 6 bugs:
  • Column: percent width is not resolved before calling measure function → returns height=1 instead of 35
  • Row: stretch is not applied to measure nodes with percent width
  • Nested containers: wrong heights → overflow (top + height > 300px)

3. Fixed tests/differential-fuzz.fuzz.ts

• Uses a random measureCustomHeight (a random number between 10 and 100)
• Added measureCustomHeight field to NodeStyle
• Both Flexily and Yoga trees now use the same custom height from the style object

4. Reverted src/layout-zero.ts

• Restored the file to its state before commit fe15082

Test Results

File	Total	Pass	Fail
yoga-comparison.test.ts	50	43	6 (all MeasureFuncPercent)
measure-percent.test.ts	6	0	6 (column + nested 3x3)
differential-fuzz.fuzz.ts	611	460	151 (all Percent Measure Leaf)

Known Bugs (all related to the same root cause)

• Phase 5 pre-measure result (height=1 with full parent width) overwrites Phase 4 final result (height=35 with resolved percent width)
• Flexily does not apply stretch to measure nodes with percent sizes in row
• Nested containers overflow because height from pre-measure is wrong (too small)

[neftaly]

awesome, can you rewrite your history/squash your commits for the tests into just a couple? and then if you add your fix. i can review that far and then we can figure out to do with rest of issues