Fix fixFlexBasisFitContent causing layout collapse on re-layout #1964
Fix fixFlexBasisFitContent causing layout collapse on re-layout #1964scorsin-oai wants to merge 1 commit into
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An explicit flex-basis: 0 on an auto-sized, non-growing item should not make Yoga skip intrinsic measurement. Before this change, computeFlexBasisForChild only ignored the resolved zero basis while the owner main-axis size was indefinite. If a later pass had a definite owner main-axis size, the same node started using the resolved zero flex basis, so its main size could flip from content-sized to zero without a style change. That made layout depend on the shape of the previous layout pass. A measured label or a wrapper around measured content could be validly measured on the first pass, then collapse after the measured leaf was dirtied and the owner was laid out with a definite width or height. Runtime viewport and view-inflation layers can then treat visible descendants as outside a zero-sized ancestor. When FixFlexBasisFitContent is enabled, make explicit zero flex-basis deterministic for auto-sized, non-growing items by keeping them on the measurement path in both row and column directions. This applies to measured leaves, wrapper containers, 0%, padded containers, nested wrappers, and web-default shrink. Growing flex items still use zero basis for normal flex distribution, and items with an explicit main-axis size continue to let flex-basis win. Add focused tests for the original two-pass collapse in both axes and for related tree shapes that would otherwise hit the same root cause: direct measured children, first-definite layouts, percent zero basis, padding, nested wrappers, and web-default shrink. Add guardrails for flex-growing zero-basis items and explicit main-axis size behavior.
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This change fixes an issue where nodes could collapse to 0 on re-layout when fixFlexBasisFitContent is enabled.
This is the setup:
Repro sequence:
Yoga measured an auto-sized flex-basis: 0 item when the parent’s main-axis size was indefinite, so it got its intrinsic content size. On a later layout pass with a definite parent size, Yoga treated the resolved 0 basis as authoritative, skipped measurement, and collapsed the same item to 0.
What the fix does:
For FixFlexBasisFitContent, explicit flex-basis: 0 on an auto-sized, non-growing item stays on the measurement path, so its size is based on content consistently across layout passes. Flex-growing zero-basis items still use zero basis for normal flex distribution.