Spec-correct CSS Flexbox §4.5 auto-min-size opt-in on YGConfig (re-land) (#57015)

Summary:
X-link: react/yoga#1968

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

This re-land additionally fixes a correctness gap in the original D105720159 design: it claimed "Default configs carry the bit (preserves today's behaviour); existing trees see no change" — but `LayoutConformance::Strict` in `YogaLayoutableShadowNode::resolveErrata` returned `YGErrataNone`, which clears every errata bit *including* the new `MinSizeUndefinedInsteadOfAuto` (bit 8). Since `react-strict-dom` sets `experimental_layoutConformance="strict"` on every native View, this implicitly opts every RSD-using surface into the new auto-min probe. That's the exact path Airwave's tests took to hit the original NPE.

Change: `LayoutConformance::Strict` now returns `YGErrataMinSizeUndefinedInsteadOfAuto` instead of `YGErrataNone`. Strict mode keeps every other CSS conformance behavior intact; only the new auto-min feature stays opt-in via explicit `YGConfig` setup. This matches the design pattern Litho uses in the child diff (`ComponentsConfiguration.useAutoMinSize` flag, gated independently of any strict-mode plumbing).

Original summary follows:

X-link: react/yoga#1966

Pull Request resolved: #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. **`LayoutConformance::Strict` also keeps the bit set** — the new feature is strictly opt-in, not inferred from strict-mode CSS conformance.

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: D107183851

Author: adityasharat

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlags.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<86c797c19cc585b74714ca3aa75bbd6d>>
+ * @generated SignedSource<<7e91da9df64ce42424101d7d72356c4a>>
  */
 
 /**
@@ -168,6 +168,12 @@ public object ReactNativeFeatureFlags {
   @JvmStatic
   public fun enableFabricLogs(): Boolean = accessor.enableFabricLogs()
 
+  /**
+   * Enables CSS Flexbox §4.5 automatic minimum sizing under strict layout conformance. When enabled, a flex item with an undefined main-axis `min-width`/`min-height` under strict conformance receives a content-derived minimum size (per spec) instead of an undefined (0) minimum. Defaults off so the behaviour can be ramped independently of strict conformance.
+   */
+  @JvmStatic
+  public fun enableFlexboxAutoMinSizeInStrictMode(): Boolean = accessor.enableFlexboxAutoMinSizeInStrictMode()
+
   /**
    * Enables font scale changes updating layout for measurable nodes.
    */

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<d71556cf1226fe6a41dd388568153d3a>>
+ * @generated SignedSource<<3c0e10dee93b76f3e66ca79d26f2b4f2>>
  */
 
 /**
@@ -43,6 +43,7 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
   private var enableExclusivePropsUpdateAndroidCache: Boolean? = null
   private var enableFabricCommitBranchingCache: Boolean? = null
   private var enableFabricLogsCache: Boolean? = null
+  private var enableFlexboxAutoMinSizeInStrictModeCache: Boolean? = null
   private var enableFontScaleChangesUpdatingLayoutCache: Boolean? = null
   private var enableIOSTextBaselineOffsetPerLineCache: Boolean? = null
   private var enableIOSViewClipToPaddingBoxCache: Boolean? = null
@@ -315,6 +316,15 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
     return cached
   }
 
+  override fun enableFlexboxAutoMinSizeInStrictMode(): Boolean {
+    var cached = enableFlexboxAutoMinSizeInStrictModeCache
+    if (cached == null) {
+      cached = ReactNativeFeatureFlagsCxxInterop.enableFlexboxAutoMinSizeInStrictMode()
+      enableFlexboxAutoMinSizeInStrictModeCache = cached
+    }
+    return cached
+  }
+
   override fun enableFontScaleChangesUpdatingLayout(): Boolean {
     var cached = enableFontScaleChangesUpdatingLayoutCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxInterop.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<2ee82b1e1dcae3ea10dbd92549d65a6c>>
+ * @generated SignedSource<<e9cc7d01ac1884710f131fbf375f3502>>
  */
 
 /**
@@ -74,6 +74,8 @@ public object ReactNativeFeatureFlagsCxxInterop {
 
   @DoNotStrip @JvmStatic public external fun enableFabricLogs(): Boolean
 
+  @DoNotStrip @JvmStatic public external fun enableFlexboxAutoMinSizeInStrictMode(): Boolean
+
   @DoNotStrip @JvmStatic public external fun enableFontScaleChangesUpdatingLayout(): Boolean
 
   @DoNotStrip @JvmStatic public external fun enableIOSTextBaselineOffsetPerLine(): Boolean

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsDefaults.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<738a114e73ddb940fb14efd0dff79d1b>>
+ * @generated SignedSource<<061d668cf04041f4d3d2f48f11dc739f>>
  */
 
 /**
@@ -69,6 +69,8 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun enableFabricLogs(): Boolean = false
 
+  override fun enableFlexboxAutoMinSizeInStrictMode(): Boolean = false
+
   override fun enableFontScaleChangesUpdatingLayout(): Boolean = true
 
   override fun enableIOSTextBaselineOffsetPerLine(): Boolean = false

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsLocalAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<d5b84c7e0c58f61d891e0dd63f61b4c0>>
+ * @generated SignedSource<<fa85d53197cbdce6b1373fbadf3cf2b9>>
  */
 
 /**
@@ -47,6 +47,7 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
   private var enableExclusivePropsUpdateAndroidCache: Boolean? = null
   private var enableFabricCommitBranchingCache: Boolean? = null
   private var enableFabricLogsCache: Boolean? = null
+  private var enableFlexboxAutoMinSizeInStrictModeCache: Boolean? = null
   private var enableFontScaleChangesUpdatingLayoutCache: Boolean? = null
   private var enableIOSTextBaselineOffsetPerLineCache: Boolean? = null
   private var enableIOSViewClipToPaddingBoxCache: Boolean? = null
@@ -342,6 +343,16 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
     return cached
   }
 
+  override fun enableFlexboxAutoMinSizeInStrictMode(): Boolean {
+    var cached = enableFlexboxAutoMinSizeInStrictModeCache
+    if (cached == null) {
+      cached = currentProvider.enableFlexboxAutoMinSizeInStrictMode()
+      accessedFeatureFlags.add("enableFlexboxAutoMinSizeInStrictMode")
+      enableFlexboxAutoMinSizeInStrictModeCache = cached
+    }
+    return cached
+  }
+
   override fun enableFontScaleChangesUpdatingLayout(): Boolean {
     var cached = enableFontScaleChangesUpdatingLayoutCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsOverrides_RNOSS_Experimental_Android.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<c481d046dea2f8c8ca77b70d41f86430>>
+ * @generated SignedSource<<21e8d5e2a4a37e0a51f25609b80f4924>>
  */
 
 /**
@@ -25,6 +25,8 @@ public open class ReactNativeFeatureFlagsOverrides_RNOSS_Experimental_Android :
 
   override fun cxxNativeAnimatedEnabled(): Boolean = true
 
+  override fun enableFlexboxAutoMinSizeInStrictMode(): Boolean = true
+
   override fun enableRuntimeSchedulerQueueClearingOnError(): Boolean = true
 
   override fun enableSchedulerDelegateInvalidation(): Boolean = true

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsProvider.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<a3dbeb4eec6efecc4fc355b15a984e58>>
+ * @generated SignedSource<<a460b28871fc3f928dcc2d1a3bf66422>>
  */
 
 /**
@@ -69,6 +69,8 @@ public interface ReactNativeFeatureFlagsProvider {
 
   @DoNotStrip public fun enableFabricLogs(): Boolean
 
+  @DoNotStrip public fun enableFlexboxAutoMinSizeInStrictMode(): Boolean
+
   @DoNotStrip public fun enableFontScaleChangesUpdatingLayout(): Boolean
 
   @DoNotStrip public fun enableIOSTextBaselineOffsetPerLine(): Boolean

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

@@ -19,8 +19,23 @@ public abstract class YogaConfig {
 
   public abstract fun setErrata(errata: YogaErrata)
 
+  /**
+   * Sets the errata bitmask directly from an [Int]. Use this when combining multiple [YogaErrata]
+   * values (e.g., `YogaErrata.CLASSIC.intValue() and
+   * YogaErrata.STRETCH_FLEX_BASIS.intValue().inv()`) — the [YogaErrata] enum cannot represent
+   * arbitrary bitmask combinations.
+   */
+  public abstract fun setErrata(errata: Int)
+
   public abstract fun getErrata(): YogaErrata
 
+  /**
+   * Returns the errata bitmask as a raw [Int]. Use this companion to [setErrata] (Int) when the
+   * stored bitmask combines bits in a way the [YogaErrata] enum cannot represent — calling
+   * [getErrata] in that case throws [IllegalArgumentException] from `YogaErrata.fromInt`.
+   */
+  public abstract fun getErrataInt(): Int
+
   public abstract fun setLogger(logger: YogaLogger?)
 
   public abstract fun getLogger(): YogaLogger?

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

@@ -50,9 +50,15 @@ private constructor(@JvmField protected var nativePointer: Long) : YogaConfig()
     YogaNative.jni_YGConfigSetErrataJNI(nativePointer, errata.intValue())
   }
 
+  public override fun setErrata(errata: Int) {
+    YogaNative.jni_YGConfigSetErrataJNI(nativePointer, errata)
+  }
+
   public override fun getErrata(): YogaErrata =
       YogaErrata.fromInt(YogaNative.jni_YGConfigGetErrataJNI(nativePointer))
 
+  public override fun getErrataInt(): Int = YogaNative.jni_YGConfigGetErrataJNI(nativePointer)
+
   public override fun setLogger(logger: YogaLogger?) {
     _logger = logger
     YogaNative.jni_YGConfigSetLoggerJNI(nativePointer, logger)

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

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