fix a regression introduced by fixYogaFlexBasisFitContentInMainAxis feature flag

packages/react-native/Libraries/Components/View/__tests__/View-flexBasisFitContent-itest.js

@@ -0,0 +1,87 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @fantom_flags fixYogaFlexBasisFitContentInMainAxis:*
+ * @format
+ */
+
+import '@react-native/fantom/src/setUpDefaultReactNativeEnvironment';
+
+import type {HostInstance} from 'react-native';
+
+import ensureInstance from '../../../../src/private/__tests__/utilities/ensureInstance';
+import * as Fantom from '@react-native/fantom';
+import * as React from 'react';
+import {createRef} from 'react';
+import {ScrollView, StyleSheet, View} from 'react-native';
+import ReactNativeElement from 'react-native/src/private/webapis/dom/nodes/ReactNativeElement';
+
+const VIEWPORT_WIDTH = 402;
+const VIEWPORT_HEIGHT = 760;
+const FEED_CONTENT_HEIGHT = 1800;
+
+test('auto-height wrapper around a feed ScrollView stays bounded by the viewport', () => {
+  const root = Fantom.createRoot({
+    viewportWidth: VIEWPORT_WIDTH,
+    viewportHeight: VIEWPORT_HEIGHT,
+  });
+
+  const wrapperRef = createRef<HostInstance>();
+  const scrollViewRef = createRef<HostInstance>();
+  const feedContentRef = createRef<HostInstance>();
+
+  Fantom.runTask(() => {
+    root.render(
+      <View collapsable={false} style={styles.screen}>
+        <View collapsable={false} ref={wrapperRef} style={styles.feedWrapper}>
+          <ScrollView
+            collapsable={false}
+            ref={scrollViewRef}
+            style={styles.feed}>
+            <View
+              collapsable={false}
+              ref={feedContentRef}
+              style={styles.feedContent}
+            />
+          </ScrollView>
+        </View>
+      </View>,
+    );
+  });
+
+  const wrapper = ensureInstance(wrapperRef.current, ReactNativeElement);
+  const scrollView = ensureInstance(scrollViewRef.current, ReactNativeElement);
+  const feedContent = ensureInstance(
+    feedContentRef.current,
+    ReactNativeElement,
+  );
+
+  const wrapperRect = wrapper.getBoundingClientRect();
+  const scrollViewRect = scrollView.getBoundingClientRect();
+  const feedContentRect = feedContent.getBoundingClientRect();
+
+  expect(wrapperRect.height).toBe(VIEWPORT_HEIGHT);
+  expect(scrollViewRect.height).toBe(VIEWPORT_HEIGHT);
+  expect(feedContentRect.height).toBe(FEED_CONTENT_HEIGHT);
+});
+
+const styles = StyleSheet.create({
+  feed: {
+    width: VIEWPORT_WIDTH,
+  },
+  feedContent: {
+    height: FEED_CONTENT_HEIGHT,
+    width: VIEWPORT_WIDTH,
+  },
+  feedWrapper: {
+    flexGrow: 1,
+  },
+  screen: {
+    height: VIEWPORT_HEIGHT,
+    width: VIEWPORT_WIDTH,
+  },
+});

packages/react-native/ReactCommon/yoga/yoga/algorithm/CalculateLayout.cpp

@@ -177,9 +177,11 @@ static void computeFlexBasisForChild(
 
     // For height in the main axis (column direction): when the
     // FixFlexBasisFitContent feature is enabled, skip FitContent for
-    // non-measure container children. This makes the flex basis independent
-    // of the parent's content-determined height, preventing unnecessary
-    // re-measurement cascades when a sibling changes size in a ScrollView.
+    // non-measure container children inside scroll subtrees. This makes the
+    // flex basis independent of content-determined heights, preventing
+    // unnecessary re-measurement cascades when a sibling changes size in a
+    // ScrollView, while preserving viewport bounds for wrappers outside the
+    // scroll subtree.
     //
     // We only optimize the height (column) axis because text wrapping depends
     // on width constraints propagating through container nodes. Removing
@@ -188,8 +190,16 @@ static void computeFlexBasisForChild(
     bool applyHeightFitContent =
         isMainAxisRow || node->style().overflow() != Overflow::Scroll;
     if (fixFlexBasisFitContent) {
+      bool nodeHasScrollAncestor = false;
+      for (auto owner = node->getOwner(); owner != nullptr;
+           owner = owner->getOwner()) {
+        if (owner->style().overflow() == Overflow::Scroll) {
+          nodeHasScrollAncestor = true;
+          break;
+        }
+      }
       applyHeightFitContent = isMainAxisRow ||
-          (child->hasMeasureFunc() &&
+          ((child->hasMeasureFunc() || !nodeHasScrollAncestor) &&
            node->style().overflow() != Overflow::Scroll);
     }
     if (applyHeightFitContent && yoga::isUndefined(childHeight) &&