Re-land: fixYogaFlexBasisFitContentInMainAxis (facebook#56064)

Summary:

X-link: facebook/yoga#1917

Re-land of D94658492 with fixes, which was reverted in D95669495.

## Context

D94658492 added the `fixYogaFlexBasisFitContentInMainAxis` flag to avoid unnecessary re-measurement cascades in Yoga. When Yoga computes flex basis for container children, the legacy behavior applies a `FitContent` constraint in the main axis, bounding the child's measurement by the parent's available space. This creates a dependency between the child's flex basis and the parent's content-determined size — when one sibling changes size, all siblings get re-measured and their shadow nodes get cloned unnecessarily.

The fix switches from `FitContent` to `MaxContent` for non-measure container children under auto-height parents, making each child's flex basis independent of the parent's size.

## What went wrong

D94658492 modeled the fix as a `YogaErrata` bit (`FLEX_BASIS_FIT_CONTENT_IN_MAIN_AXIS`). Errata flags are bitmasks, and apps that opt into `ALL` or `CLASSIC` errata (like IGVR and Airwave) inadvertently picked up the new behavior without explicitly enabling the feature flag, causing breakages.

## What changed in this re-land

This diff models the fix as a `YogaExperimentalFeature` (`FIX_FLEX_BASIS_FIT_CONTENT`) instead of a `YogaErrata` bit. Experimental features are individually opt-in, so existing apps won't accidentally pick up the change.

This diff only wires up the RN feature flag infrastructure (flag defaults to `false`). The iOS MobileConfig override and the Yoga layout logic will be landed in follow-up diffs.

changelog: [internal]

Reviewed By: javache, NickGerleman

Differential Revision: D95852922

Author: sammy-SC

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<<039798c50526ff1abf33bc7987aa78a9>>
+ * @generated SignedSource<<5144fb0350b71394206d614c68ef87f0>>
  */
 
 /**
@@ -390,6 +390,12 @@ public object ReactNativeFeatureFlags {
   @JvmStatic
   public fun fixTextClippingAndroid15useBoundsForWidth(): Boolean = accessor.fixTextClippingAndroid15useBoundsForWidth()
 
+  /**
+   * Fix flex basis computation to not apply FitContent constraint in the main axis for non-measure container nodes, preventing unnecessary re-measurement in scroll containers.
+   */
+  @JvmStatic
+  public fun fixYogaFlexBasisFitContentInMainAxis(): Boolean = accessor.fixYogaFlexBasisFitContentInMainAxis()
+
   /**
    * Enable system assertion validating that Fusebox is configured with a single host. When set, the CDP backend will dynamically disable features (Perf and Network) in the event that multiple hosts are registered (undefined behaviour), and broadcast this over `ReactNativeApplication.systemStateChanged`.
    */

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<<cbc85fcd815ba2585166a53e7b410f30>>
+ * @generated SignedSource<<d284f066f036908977797a381a044dfa>>
  */
 
 /**
@@ -80,6 +80,7 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
   private var fixFindShadowNodeByTagRaceConditionCache: Boolean? = null
   private var fixMappingOfEventPrioritiesBetweenFabricAndReactCache: Boolean? = null
   private var fixTextClippingAndroid15useBoundsForWidthCache: Boolean? = null
+  private var fixYogaFlexBasisFitContentInMainAxisCache: Boolean? = null
   private var fuseboxAssertSingleHostStateCache: Boolean? = null
   private var fuseboxEnabledReleaseCache: Boolean? = null
   private var fuseboxFrameRecordingEnabledCache: Boolean? = null
@@ -650,6 +651,15 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
     return cached
   }
 
+  override fun fixYogaFlexBasisFitContentInMainAxis(): Boolean {
+    var cached = fixYogaFlexBasisFitContentInMainAxisCache
+    if (cached == null) {
+      cached = ReactNativeFeatureFlagsCxxInterop.fixYogaFlexBasisFitContentInMainAxis()
+      fixYogaFlexBasisFitContentInMainAxisCache = cached
+    }
+    return cached
+  }
+
   override fun fuseboxAssertSingleHostState(): Boolean {
     var cached = fuseboxAssertSingleHostStateCache
     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<<3d472893c05bdee6e09f834f52d3d92f>>
+ * @generated SignedSource<<de1c66a540520cd88c4d358ba30f2c6d>>
  */
 
 /**
@@ -148,6 +148,8 @@ public object ReactNativeFeatureFlagsCxxInterop {
 
   @DoNotStrip @JvmStatic public external fun fixTextClippingAndroid15useBoundsForWidth(): Boolean
 
+  @DoNotStrip @JvmStatic public external fun fixYogaFlexBasisFitContentInMainAxis(): Boolean
+
   @DoNotStrip @JvmStatic public external fun fuseboxAssertSingleHostState(): Boolean
 
   @DoNotStrip @JvmStatic public external fun fuseboxEnabledRelease(): 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<<29f7031f91527f41f2f184596c542a5b>>
+ * @generated SignedSource<<ab3b1d2277b8cc9db1708ef94515fb35>>
  */
 
 /**
@@ -143,6 +143,8 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun fixTextClippingAndroid15useBoundsForWidth(): Boolean = false
 
+  override fun fixYogaFlexBasisFitContentInMainAxis(): Boolean = false
+
   override fun fuseboxAssertSingleHostState(): Boolean = true
 
   override fun fuseboxEnabledRelease(): 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<<014ee4afdf58a61c9974df198068d81a>>
+ * @generated SignedSource<<7b87f5541ecf881d8ce51c5edd5b99b0>>
  */
 
 /**
@@ -84,6 +84,7 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
   private var fixFindShadowNodeByTagRaceConditionCache: Boolean? = null
   private var fixMappingOfEventPrioritiesBetweenFabricAndReactCache: Boolean? = null
   private var fixTextClippingAndroid15useBoundsForWidthCache: Boolean? = null
+  private var fixYogaFlexBasisFitContentInMainAxisCache: Boolean? = null
   private var fuseboxAssertSingleHostStateCache: Boolean? = null
   private var fuseboxEnabledReleaseCache: Boolean? = null
   private var fuseboxFrameRecordingEnabledCache: Boolean? = null
@@ -714,6 +715,16 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
     return cached
   }
 
+  override fun fixYogaFlexBasisFitContentInMainAxis(): Boolean {
+    var cached = fixYogaFlexBasisFitContentInMainAxisCache
+    if (cached == null) {
+      cached = currentProvider.fixYogaFlexBasisFitContentInMainAxis()
+      accessedFeatureFlags.add("fixYogaFlexBasisFitContentInMainAxis")
+      fixYogaFlexBasisFitContentInMainAxisCache = cached
+    }
+    return cached
+  }
+
   override fun fuseboxAssertSingleHostState(): Boolean {
     var cached = fuseboxAssertSingleHostStateCache
     if (cached == null) {

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<<acd57b19a67924a91c6b25904cb24d3b>>
+ * @generated SignedSource<<f34b257861830bae7012fc5201904831>>
  */
 
 /**
@@ -143,6 +143,8 @@ public interface ReactNativeFeatureFlagsProvider {
 
   @DoNotStrip public fun fixTextClippingAndroid15useBoundsForWidth(): Boolean
 
+  @DoNotStrip public fun fixYogaFlexBasisFitContentInMainAxis(): Boolean
+
   @DoNotStrip public fun fuseboxAssertSingleHostState(): Boolean
 
   @DoNotStrip public fun fuseboxEnabledRelease(): Boolean

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

@@ -10,7 +10,8 @@
 package com.facebook.yoga;
 
 public enum YogaExperimentalFeature {
-  WEB_FLEX_BASIS(0);
+  WEB_FLEX_BASIS(0),
+  FIX_FLEX_BASIS_FIT_CONTENT(1);
 
   private final int mIntValue;
 
@@ -25,6 +26,7 @@ public int intValue() {
   public static YogaExperimentalFeature fromInt(int value) {
     switch (value) {
       case 0: return WEB_FLEX_BASIS;
+      case 1: return FIX_FLEX_BASIS_FIT_CONTENT;
       default: throw new IllegalArgumentException("Unknown enum value: " + value);
     }
   }

packages/react-native/ReactAndroid/src/main/jni/react/featureflags/JReactNativeFeatureFlagsCxxInterop.cpp

@@ -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<<a753500d987b8719f0ba1bba8d3e4dc4>>
+ * @generated SignedSource<<b4670c40175b42e04eb8f03b752a0c00>>
  */
 
 /**
@@ -399,6 +399,12 @@ class ReactNativeFeatureFlagsJavaProvider
     return method(javaProvider_);
   }
 
+  bool fixYogaFlexBasisFitContentInMainAxis() override {
+    static const auto method =
+        getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("fixYogaFlexBasisFitContentInMainAxis");
+    return method(javaProvider_);
+  }
+
   bool fuseboxAssertSingleHostState() override {
     static const auto method =
         getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("fuseboxAssertSingleHostState");
@@ -877,6 +883,11 @@ bool JReactNativeFeatureFlagsCxxInterop::fixTextClippingAndroid15useBoundsForWid
   return ReactNativeFeatureFlags::fixTextClippingAndroid15useBoundsForWidth();
 }
 
+bool JReactNativeFeatureFlagsCxxInterop::fixYogaFlexBasisFitContentInMainAxis(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
+  return ReactNativeFeatureFlags::fixYogaFlexBasisFitContentInMainAxis();
+}
+
 bool JReactNativeFeatureFlagsCxxInterop::fuseboxAssertSingleHostState(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
   return ReactNativeFeatureFlags::fuseboxAssertSingleHostState();
@@ -1233,6 +1244,9 @@ void JReactNativeFeatureFlagsCxxInterop::registerNatives() {
       makeNativeMethod(
         "fixTextClippingAndroid15useBoundsForWidth",
         JReactNativeFeatureFlagsCxxInterop::fixTextClippingAndroid15useBoundsForWidth),
+      makeNativeMethod(
+        "fixYogaFlexBasisFitContentInMainAxis",
+        JReactNativeFeatureFlagsCxxInterop::fixYogaFlexBasisFitContentInMainAxis),
       makeNativeMethod(
         "fuseboxAssertSingleHostState",
         JReactNativeFeatureFlagsCxxInterop::fuseboxAssertSingleHostState),

packages/react-native/ReactAndroid/src/main/jni/react/featureflags/JReactNativeFeatureFlagsCxxInterop.h

@@ -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<<6ff305bf95e95cd8a65c138fc24b43f8>>
+ * @generated SignedSource<<5433b4a2f4a0574591a38017422edac8>>
  */
 
 /**
@@ -210,6 +210,9 @@ class JReactNativeFeatureFlagsCxxInterop
   static bool fixTextClippingAndroid15useBoundsForWidth(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 
+  static bool fixYogaFlexBasisFitContentInMainAxis(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
+
   static bool fuseboxAssertSingleHostState(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlags.cpp

@@ -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<<903b6404deb3339d2cfeced5be354134>>
+ * @generated SignedSource<<bfb72cee88230c56d2c101be808ef300>>
  */
 
 /**
@@ -266,6 +266,10 @@ bool ReactNativeFeatureFlags::fixTextClippingAndroid15useBoundsForWidth() {
   return getAccessor().fixTextClippingAndroid15useBoundsForWidth();
 }
 
+bool ReactNativeFeatureFlags::fixYogaFlexBasisFitContentInMainAxis() {
+  return getAccessor().fixYogaFlexBasisFitContentInMainAxis();
+}
+
 bool ReactNativeFeatureFlags::fuseboxAssertSingleHostState() {
   return getAccessor().fuseboxAssertSingleHostState();
 }