alignContent: stretch doesn't actually stretch rows in a flexWrap: wrap layout

[benjdreier]

Description

I'm seeing a big discrepency between react native web and iOS/Android for the behavior of alignContent: stretch for views with flexWrap: wrap and flexDirection: column. I noticed the discrepency when I tried to set the alignSelf property of an individual element inside the flex container.

On web, alignContent: stretch works as expected. Each row becomes tall enough that I can align elements individually within their respective row using alignSelf

But on iOS and Android, alignSelf initially seems to have no effect. This is because, even though alignContent: stretch is set, the implicit row containers don't actually stretch out to their full height. Rows begin in their expected positions, but the height of each row is implicitly fit to contents instead of stretching. This means my elements can't align themselves properly — they have nowhere to go, their container is too restricted.

An almost-workaround I found, for example, is to add an empty view inside the flex container that has the desired height of a row — that makes the row stretch out enough so that other elements are visibly aligned correctly. But this isn't a real option for me — first of all, it breaks any layout that depends on the number  I can't guarantee the height or number of any particular element, as I need to build very generically.

Steps to reproduce

See expo snack
In general, I believe:

1. Create a flex container with "flexDirection": "row", "flexWrap": "wrap", "alignContent": "stretch"
2. Add a child with "alignSelf": "flex-end", or `"alignSelf": "center"
3. Observe that alignSelf changes the element's position on web, as expect, but has no effect on ios/android

React Native Version

0.76.3

Affected Platforms

Runtime - iOS, Runtime - Android

Output of npx @react-native-community/cli info

System:
  OS: macOS 14.7.1
  CPU: (8) arm64 Apple M2
  Memory: 154.44 MB / 16.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.14.0
    path: ~/.nvm/versions/node/v22.14.0/bin/node
  Yarn: Not Found
  npm:
    version: 10.9.2
    path: ~/.nvm/versions/node/v22.14.0/bin/npm
  Watchman: Not Found
Managers:
  CocoaPods:
    version: 1.15.2
    path: /opt/homebrew/lib/ruby/gems/3.3.0/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.1
      - iOS 18.1
      - macOS 15.1
      - tvOS 18.1
      - visionOS 2.1
      - watchOS 11.1
  Android SDK:
    API Levels:
      - "34"
      - "35"
    Build Tools:
      - 33.0.1
      - 34.0.0
      - 35.0.0
    System Images:
      - android-35 | ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2024.2 AI-242.23339.11.2421.12700392
  Xcode:
    version: 16.1/16B40
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.13
    path: /usr/bin/javac
  Ruby:
    version: 3.3.6
    path: /opt/homebrew/opt/ruby/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 18.3.1
    wanted: 18.3.1
  react-native:
    installed: 0.76.6
    wanted: 0.76.6
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

N/A — layout bug

Reproducer

https://snack.expo.dev/OT-sH48w22h3vDCqD6nra?platform=ios

Screenshots and Videos

Web (Expected Behavior)

Mobile (Rows are too short, can't align properly)

[react-native-bot]

Tip

Newer version available: You are on a supported minor version, but it looks like there's a newer patch available - 0.76.7. Please upgrade to the highest patch for your minor or latest and verify if the issue persists (alternatively, create a new project and repro the issue in it). If it does not repro, please let us know so we can close out this issue. This helps us ensure we are looking at issues that still exist in the most recent releases.

[react-native-bot]

Tip

Newer version available: You are on a supported minor version, but it looks like there's a newer patch available - undefined. Please upgrade to the highest patch for your minor or latest and verify if the issue persists (alternatively, create a new project and repro the issue in it). If it does not repro, please let us know so we can close out this issue. This helps us ensure we are looking at issues that still exist in the most recent releases.