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Spec-correct CSS Flexbox §4.5 auto-min-size opt-in on YGConfig (re-land) (#1966)#1967

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Spec-correct CSS Flexbox §4.5 auto-min-size opt-in on YGConfig (re-land) (#1966)#1967
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Summary:
X-link: facebook/react-native#57036

Re-land of D105720159, originally reverted (revert: 0e642b96c7e2) due to a latent NPE in ReactProgressBarViewManager.kt and ReactSwitchManager.kt (instagram-internal) — both fixed in the prior diffs in this stack. Crash and broken e2e tests reported in T273821098 / P2359486686.

Original summary:

X-link: facebook/react-native#57015

Implements CSS Flexbox §4.5 automatic minimum sizing in Yoga. When opted in on a YGConfig, every flex item whose main-axis min-{width,height} is undefined receives a content-derived floor — min(min-content, specified-size, max-size) plus any aspect-ratio-transferred lower bound — so it cannot shrink below the size CSS browsers would honor.

How to opt in: clear the new YGErrataMinSizeUndefinedInsteadOfAuto errata bit on the config. Default configs carry the bit (preserves today's behaviour); existing trees see no change. The bit is added to YGErrataClassic so consumers using that constant continue to get the same default.

See D105720159 for full details on precedence rules, container recursion semantics, and per-item opt-outs.

Changelog:
[General][Added] - Add CSS Flexbox §4.5 automatic minimum sizing. Opt in by clearing the new YGErrataMinSizeUndefinedInsteadOfAuto errata bit on YGConfig.

Differential Revision: D107181739

…nd) (facebook#1966)

Summary:
X-link: facebook/react-native#57036

Re-land of D105720159, originally reverted (revert: 0e642b96c7e2) due to a latent NPE in `ReactProgressBarViewManager.kt` and `ReactSwitchManager.kt` (instagram-internal) — both fixed in the prior diffs in this stack. Crash and broken e2e tests reported in T273821098 / P2359486686.

Original summary:

X-link: facebook/react-native#57015

Implements CSS Flexbox §4.5 automatic minimum sizing in Yoga. When opted in on a `YGConfig`, every flex item whose main-axis `min-{width,height}` is undefined receives a content-derived floor — `min(min-content, specified-size, max-size)` plus any aspect-ratio-transferred lower bound — so it cannot shrink below the size CSS browsers would honor.

How to opt in: clear the new `YGErrataMinSizeUndefinedInsteadOfAuto` errata bit on the config. Default configs carry the bit (preserves today's behaviour); existing trees see no change. The bit is added to `YGErrataClassic` so consumers using that constant continue to get the same default.

See D105720159 for full details on precedence rules, container recursion semantics, and per-item opt-outs.

Changelog:
[General][Added] - Add CSS Flexbox §4.5 automatic minimum sizing. Opt in by clearing the new `YGErrataMinSizeUndefinedInsteadOfAuto` errata bit on `YGConfig`.

Differential Revision: D107181739
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meta-codesync Bot commented Jun 1, 2026

@adityasharat has exported this pull request. If you are a Meta employee, you can view the originating Diff in D107181739.

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