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Spec-correct CSS Flexbox §4.5 auto-min-size opt-in on YGConfig
Summary: Adds a `YGConfig`-level opt-in (`YGConfigSetUseAutoMinSize`) for CSS Flexbox §4.5 automatic minimum sizing. When enabled, all flex items under the config get a content-derived minimum size (`min(min-content, specified-size, max-size)` plus any aspect-ratio lower bound) unless an explicit `min-{width,height}: 0` is set, mirroring the CSS escape hatch. **Why a real spec implementation (not `computedFlexBasis`):** - *Under-protection*: `flex: 1` sets `flex-basis: 0`, so basis-floor is 0 and offers no protection—items with unbreakable content can clip. Browsers protect at min-content. - *Over-protection*: An item with `width: 100` and 40px-tall content should shrink to 40, but basis approximation floors at 100, causing overflow. **Implementation details:** - Mirrors RenderCore's FlexLayout (`xplat/flexlayout/`): recursive min-content probe (`computeMinContentMainSize`), per-item floor with §4.5 caps (`computeAutoMinMainSize`), and a wrapper (`boundAxisWithAutoMin`) for shrink distribution. - Yoga changes (`xplat/yoga` and `xplat/js/react-native-github/.../yoga`): - `Config::useAutoMinSize_` field with setter/getter; included in `configUpdateInvalidatesLayout`. - C API (`YGConfigSetUseAutoMinSize` / `YGConfigGetUseAutoMinSize`), JNI binding, Kotlin wrappers (`YogaConfig`, `YogaConfigJNIBase`, `YogaNative`), matching `useWebDefaults`. Off by default. - `LayoutResults::computedAutoMinMainSize` is a transient `FloatOptional` cached per-item per layout pass. - `computeMinContentMainSize` is the recursive probe; leaves with measure function are called with `AtMost 0` along the main axis. - `computeAutoMinMainSize` applies §4.5 sequencing: skips when feature is off, explicit min, or `display:none`; returns 0 for `overflow != visible`; computes `min(content, specified)` or `min(content, transferred)` (aspect-ratio), caps by max, floors at 0. - `boundAxisWithAutoMin` wraps `boundAxis` with the cached lower bound; shrink/grow result clamping uses this wrapper. - `resolveFlexibleLength` seeds each `itemsInFlow` entry's `computedAutoMinMainSize` before the first pass when the config flag is on, clears cache otherwise. **Performance:** One min-content probe per opted-in flex item per layout pass. Items with explicit main-axis min styles skip the probe. Off by default—no impact on existing trees. **Reference:** [https://www.w3.org/TR/css-flexbox-1/#min-size-auto](https://www.w3.org/TR/css-flexbox-1/#min-size-auto) **Changelog:** - Add `YGConfigSetUseAutoMinSize` to enable CSS Flexbox §4.5 automatic minimum sizing for flex items. Reviewed By: fbcbl Differential Revision: D105720159
1 parent f363f6b commit 78d75a7

27 files changed

Lines changed: 697 additions & 4 deletions

‎packages/react-native/ReactAndroid/src/main/java/com/facebook/yoga/YogaConfig.kt‎

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@@ -19,6 +19,14 @@ public abstract class YogaConfig {
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2020
public abstract fun setErrata(errata: YogaErrata)
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/**
23+
* Sets the errata bitmask directly from an [Int]. Use this when combining multiple [YogaErrata]
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* values (e.g., `YogaErrata.CLASSIC.intValue() and
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* YogaErrata.STRETCH_FLEX_BASIS.intValue().inv()`) — the [YogaErrata] enum cannot represent
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* arbitrary bitmask combinations.
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*/
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public abstract fun setErrata(errata: Int)
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public abstract fun getErrata(): YogaErrata
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public abstract fun setLogger(logger: YogaLogger?)

‎packages/react-native/ReactAndroid/src/main/java/com/facebook/yoga/YogaConfigJNIBase.kt‎

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@@ -50,6 +50,10 @@ private constructor(@JvmField protected var nativePointer: Long) : YogaConfig()
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YogaNative.jni_YGConfigSetErrataJNI(nativePointer, errata.intValue())
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}
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public override fun setErrata(errata: Int) {
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YogaNative.jni_YGConfigSetErrataJNI(nativePointer, errata)
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}
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5357
public override fun getErrata(): YogaErrata =
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YogaErrata.fromInt(YogaNative.jni_YGConfigGetErrataJNI(nativePointer))
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‎packages/react-native/ReactAndroid/src/main/java/com/facebook/yoga/YogaErrata.kt‎

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@@ -14,6 +14,7 @@ public enum class YogaErrata(public val intValue: Int) {
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STRETCH_FLEX_BASIS(1),
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ABSOLUTE_POSITION_WITHOUT_INSETS_EXCLUDES_PADDING(2),
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ABSOLUTE_PERCENT_AGAINST_INNER_SIZE(4),
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MIN_SIZE_UNDEFINED_INSTEAD_OF_AUTO(8),
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ALL(2147483647),
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CLASSIC(2147483646);
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@@ -27,6 +28,7 @@ public enum class YogaErrata(public val intValue: Int) {
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1 -> STRETCH_FLEX_BASIS
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2 -> ABSOLUTE_POSITION_WITHOUT_INSETS_EXCLUDES_PADDING
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4 -> ABSOLUTE_PERCENT_AGAINST_INNER_SIZE
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8 -> MIN_SIZE_UNDEFINED_INSTEAD_OF_AUTO
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2147483647 -> ALL
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2147483646 -> CLASSIC
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else -> throw IllegalArgumentException("Unknown enum value: $value")

‎packages/react-native/ReactAndroid/src/main/java/com/facebook/yoga/YogaNative.kt‎

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@@ -311,6 +311,22 @@ public object YogaNative {
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@JvmStatic
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public external fun jni_YGNodeSetHasMeasureFuncJNI(nativePointer: Long, hasMeasureFunc: Boolean)
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@JvmStatic
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public external fun jni_YGNodeSetHasMinContentMeasureFuncJNI(
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nativePointer: Long,
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hasMinContentMeasureFunc: Boolean,
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)
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@JvmStatic
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public external fun jni_YGNodeSetMinContentWidthJNI(nativePointer: Long, minContentWidth: Float)
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@JvmStatic
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public external fun jni_YGNodeSetMinContentHeightJNI(nativePointer: Long, minContentHeight: Float)
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@JvmStatic public external fun jni_YGNodeGetMinContentWidthJNI(nativePointer: Long): Float
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@JvmStatic public external fun jni_YGNodeGetMinContentHeightJNI(nativePointer: Long): Float
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@JvmStatic
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public external fun jni_YGNodeSetHasBaselineFuncJNI(nativePointer: Long, hasMeasureFunc: Boolean)
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‎packages/react-native/ReactAndroid/src/main/java/com/facebook/yoga/YogaNode.kt‎

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@@ -228,6 +228,16 @@ public abstract class YogaNode : YogaProps {
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abstract override fun setMeasureFunction(measureFunction: YogaMeasureFunction?)
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abstract override fun setMinContentMeasureFunction(measureFunction: YogaMeasureFunction?)
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abstract override fun setMinContentWidth(minContentWidth: Float)
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abstract override fun setMinContentHeight(minContentHeight: Float)
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abstract override fun getMinContentWidth(): Float
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abstract override fun getMinContentHeight(): Float
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abstract override fun setBaselineFunction(yogaBaselineFunction: YogaBaselineFunction?)
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public abstract val isMeasureDefined: Boolean

‎packages/react-native/ReactAndroid/src/main/java/com/facebook/yoga/YogaNodeJNIBase.kt‎

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@@ -16,6 +16,7 @@ public abstract class YogaNodeJNIBase : YogaNode, Cloneable {
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private var config: YogaConfig? = null
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private var children: MutableList<YogaNodeJNIBase>? = null
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private var measureFunction: YogaMeasureFunction? = null
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private var minContentMeasureFunction: YogaMeasureFunction? = null
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private var baselineFunction: YogaBaselineFunction? = null
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protected var nativePointer: Long = 0
2122

@@ -46,6 +47,7 @@ public abstract class YogaNodeJNIBase : YogaNode, Cloneable {
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override fun reset() {
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measureFunction = null
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minContentMeasureFunction = null
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baselineFunction = null
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data = null
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arr = null
@@ -524,6 +526,25 @@ public abstract class YogaNodeJNIBase : YogaNode, Cloneable {
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YogaNative.jni_YGNodeSetHasMeasureFuncJNI(nativePointer, measureFunction != null)
525527
}
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529+
override fun setMinContentMeasureFunction(measureFunction: YogaMeasureFunction?) {
530+
this.minContentMeasureFunction = measureFunction
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YogaNative.jni_YGNodeSetHasMinContentMeasureFuncJNI(nativePointer, measureFunction != null)
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}
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override fun setMinContentWidth(minContentWidth: Float) {
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YogaNative.jni_YGNodeSetMinContentWidthJNI(nativePointer, minContentWidth)
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}
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override fun setMinContentHeight(minContentHeight: Float) {
539+
YogaNative.jni_YGNodeSetMinContentHeightJNI(nativePointer, minContentHeight)
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}
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override fun getMinContentWidth(): Float =
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YogaNative.jni_YGNodeGetMinContentWidthJNI(nativePointer)
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override fun getMinContentHeight(): Float =
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YogaNative.jni_YGNodeGetMinContentHeightJNI(nativePointer)
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527548
override fun setAlwaysFormsContainingBlock(alwaysFormsContainingBlock: Boolean) {
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YogaNative.jni_YGNodeSetAlwaysFormsContainingBlockJNI(
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nativePointer,
@@ -547,6 +568,27 @@ public abstract class YogaNodeJNIBase : YogaNode, Cloneable {
547568
)
548569
}
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// Native callback invoked by Yoga during the CSS Flexbox §4.5 auto-min
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// probe when a min-content measure function is registered. Mirrors
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// [measure]; see that method's note on non-overridability.
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@DoNotStrip
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public fun measureMinContent(
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width: Float,
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widthMode: Int,
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height: Float,
579+
heightMode: Int,
580+
): Long {
581+
val mf =
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checkNotNull(minContentMeasureFunction) { "Min-content measure function isn't defined!" }
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return mf.measure(
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this,
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width,
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YogaMeasureMode.fromInt(widthMode),
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height,
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YogaMeasureMode.fromInt(heightMode),
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)
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}
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override fun setBaselineFunction(yogaBaselineFunction: YogaBaselineFunction?) {
551593
baselineFunction = yogaBaselineFunction
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YogaNative.jni_YGNodeSetHasBaselineFuncJNI(nativePointer, yogaBaselineFunction != null)

‎packages/react-native/ReactAndroid/src/main/java/com/facebook/yoga/YogaProps.kt‎

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Original file line numberDiff line numberDiff line change
@@ -125,6 +125,28 @@ public interface YogaProps {
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public fun setMeasureFunction(measureFunction: YogaMeasureFunction?)
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public fun setMinContentMeasureFunction(measureFunction: YogaMeasureFunction?)
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/**
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* Sets the static min-content width used by the CSS Flexbox §4.5 automatic minimum sizing probe.
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* Pass `YogaConstants.UNDEFINED` to clear. See `YGNodeSetMinContentWidth` in the Yoga C API for
133+
* full precedence rules.
134+
*/
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public fun setMinContentWidth(minContentWidth: Float)
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/**
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* Sets the static min-content height used by the CSS Flexbox §4.5 automatic minimum sizing probe.
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* Pass `YogaConstants.UNDEFINED` to clear. See `YGNodeSetMinContentHeight` in the Yoga C API for
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* full precedence rules.
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*/
142+
public fun setMinContentHeight(minContentHeight: Float)
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/** Returns the static min-content width, or `YogaConstants.UNDEFINED` if not set. */
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public fun getMinContentWidth(): Float
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/** Returns the static min-content height, or `YogaConstants.UNDEFINED` if not set. */
148+
public fun getMinContentHeight(): Float
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128150
public fun setBaselineFunction(yogaBaselineFunction: YogaBaselineFunction?)
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/* Mutable properties - getter and setter with matching types */

‎packages/react-native/ReactAndroid/src/main/jni/first-party/yogajni/jni/YGJNIVanilla.cpp‎

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@@ -683,6 +683,81 @@ static void jni_YGNodeSetHasMeasureFuncJNI(
683683
static_cast<bool>(hasMeasureFunc) ? YGJNIMeasureFunc : nullptr);
684684
}
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static YGSize YGJNIMinContentMeasureFunc(
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YGNodeConstRef node,
688+
float width,
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YGMeasureMode widthMode,
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float height,
691+
YGMeasureMode heightMode) {
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if (auto obj = YGNodeJobject(node)) {
693+
YGTransferLayoutDirection(node, obj.get());
694+
JNIEnv* env = getCurrentEnv();
695+
auto objectClass = facebook::yoga::vanillajni::make_local_ref(
696+
env, env->GetObjectClass(obj.get()));
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static const jmethodID methodId = facebook::yoga::vanillajni::getMethodId(
698+
env, objectClass.get(), "measureMinContent", "(FIFI)J");
699+
const auto measureResult = facebook::yoga::vanillajni::callLongMethod(
700+
env, obj.get(), methodId, width, widthMode, height, heightMode);
701+
702+
uint32_t wBits = 0xFFFFFFFF & (measureResult >> 32);
703+
uint32_t hBits = 0xFFFFFFFF & measureResult;
704+
auto measuredWidth = std::bit_cast<float>(wBits);
705+
auto measuredHeight = std::bit_cast<float>(hBits);
706+
707+
return YGSize{measuredWidth, measuredHeight};
708+
} else {
709+
return YGSize{
710+
widthMode == YGMeasureModeUndefined ? 0 : width,
711+
heightMode == YGMeasureModeUndefined ? 0 : height,
712+
};
713+
}
714+
}
715+
716+
static void jni_YGNodeSetHasMinContentMeasureFuncJNI(
717+
JNIEnv* /*env*/,
718+
jobject /*obj*/,
719+
jlong nativePointer,
720+
jboolean hasMinContentMeasureFunc) {
721+
YGNodeSetMinContentMeasureFunc(
722+
_jlong2YGNodeRef(nativePointer),
723+
static_cast<bool>(hasMinContentMeasureFunc) ? YGJNIMinContentMeasureFunc
724+
: nullptr);
725+
}
726+
727+
static void jni_YGNodeSetMinContentWidthJNI(
728+
JNIEnv* /*env*/,
729+
jobject /*obj*/,
730+
jlong nativePointer,
731+
jfloat minContentWidth) {
732+
YGNodeSetMinContentWidth(
733+
_jlong2YGNodeRef(nativePointer), static_cast<float>(minContentWidth));
734+
}
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static void jni_YGNodeSetMinContentHeightJNI(
737+
JNIEnv* /*env*/,
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jobject /*obj*/,
739+
jlong nativePointer,
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jfloat minContentHeight) {
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YGNodeSetMinContentHeight(
742+
_jlong2YGNodeRef(nativePointer), static_cast<float>(minContentHeight));
743+
}
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static jfloat jni_YGNodeGetMinContentWidthJNI(
746+
JNIEnv* /*env*/,
747+
jobject /*obj*/,
748+
jlong nativePointer) {
749+
return static_cast<jfloat>(
750+
YGNodeGetMinContentWidth(_jlong2YGNodeRef(nativePointer)));
751+
}
752+
753+
static jfloat jni_YGNodeGetMinContentHeightJNI(
754+
JNIEnv* /*env*/,
755+
jobject /*obj*/,
756+
jlong nativePointer) {
757+
return static_cast<jfloat>(
758+
YGNodeGetMinContentHeight(_jlong2YGNodeRef(nativePointer)));
759+
}
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686761
static float YGJNIBaselineFunc(YGNodeConstRef node, float width, float height) {
687762
if (auto obj = YGNodeJobject(node)) {
688763
JNIEnv* env = getCurrentEnv();
@@ -1058,6 +1133,21 @@ static JNINativeMethod methods[] = {
10581133
{"jni_YGNodeSetHasMeasureFuncJNI",
10591134
"(JZ)V",
10601135
(void*)jni_YGNodeSetHasMeasureFuncJNI},
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{"jni_YGNodeSetHasMinContentMeasureFuncJNI",
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"(JZ)V",
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(void*)jni_YGNodeSetHasMinContentMeasureFuncJNI},
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{"jni_YGNodeSetMinContentWidthJNI",
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"(JF)V",
1141+
(void*)jni_YGNodeSetMinContentWidthJNI},
1142+
{"jni_YGNodeSetMinContentHeightJNI",
1143+
"(JF)V",
1144+
(void*)jni_YGNodeSetMinContentHeightJNI},
1145+
{"jni_YGNodeGetMinContentWidthJNI",
1146+
"(J)F",
1147+
(void*)jni_YGNodeGetMinContentWidthJNI},
1148+
{"jni_YGNodeGetMinContentHeightJNI",
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"(J)F",
1150+
(void*)jni_YGNodeGetMinContentHeightJNI},
10611151
{"jni_YGNodeStyleGetGapJNI", "(JI)J", (void*)jni_YGNodeStyleGetGapJNI},
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{"jni_YGNodeStyleSetGapJNI", "(JIF)V", (void*)jni_YGNodeStyleSetGapJNI},
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{"jni_YGNodeStyleSetGapPercentJNI",

‎packages/react-native/ReactCommon/yoga/yoga/YGEnums.cpp‎

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@@ -117,6 +117,8 @@ const char* YGErrataToString(const YGErrata value) {
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return "absolute-position-without-insets-excludes-padding";
118118
case YGErrataAbsolutePercentAgainstInnerSize:
119119
return "absolute-percent-against-inner-size";
120+
case YGErrataMinSizeUndefinedInsteadOfAuto:
121+
return "min-size-undefined-instead-of-auto";
120122
case YGErrataAll:
121123
return "all";
122124
case YGErrataClassic:

‎packages/react-native/ReactCommon/yoga/yoga/YGEnums.h‎

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@@ -67,6 +67,7 @@ YG_ENUM_DECL(
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YGErrataStretchFlexBasis = 1,
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YGErrataAbsolutePositionWithoutInsetsExcludesPadding = 2,
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YGErrataAbsolutePercentAgainstInnerSize = 4,
70+
YGErrataMinSizeUndefinedInsteadOfAuto = 8,
7071
YGErrataAll = 2147483647,
7172
YGErrataClassic = 2147483646)
7273
YG_DEFINE_ENUM_FLAG_OPERATORS(YGErrata)

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