react / react/react-native

layout bug: Absolutely positioned containers incorrectly constrains child view

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Beschreibung

Description

React Native's layout engine incorrectly applies width constraints from absolutely positioned parent containers to their child elements, regardless of whether the parent has explicit width constraints or dynamic sizing. When a container uses absolute positioning (position: 'absolute'), it inappropriately constrains the layout dimensions of all descendant elements, even when those children should be free to size themselves naturally. This behavior occurs whether the absolutely positioned parent has a fixed width (e.g., width: 150) or relies on content-based sizing, violating expected CSS layout principles where absolutely positioned elements with dynamic width should not impose constraints on their children. Components in normal document flow correctly allow their children to size naturally, but any absolutely positioned ancestor in the component hierarchy will impose artificial layout constraints throughout the descendant tree.

There may be an argument that if the parent has a fixed size, the constraint is valid, but if the parent is dynamically sized (to fit content), it certainly seems incorrect to me

Steps to reproduce
  1. Create a container with absolute positioning - Set position: 'absolute' on a View component, either with fixed width or
    dynamic width
  2. Add a child element that needs natural sizing - Place any child component inside the absolutely positioned container that should size itself based on its content. Using a short Text block is the easiest way
  3. Compare with normal flow container - Create an identical child component inside a container using normal document flow (no absolute positioning)
  4. Observe the constraint difference - The child in the absolutely positioned container will be artificially constrained, while the child in normal flow will size naturally

Minimal Example Structure:

// This child will be constrained
<View style={{ position: 'absolute' }}>

// This child will size naturally


Expected vs Actual Behavior:

  • Expected: Children should size naturally regardless of parent positioning method
  • Actual: Absolutely positioned parents impose width constraints on all descendants
React Native Version

0.79.2

Affected Platforms

Runtime - iOS

Output of npx @react-native-community/cli info
info Fetching system and libraries information...
System:
  OS: macOS 15.5
  CPU: (10) arm64 Apple M1 Max
  Memory: 3.99 GB / 64.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.16.0
    path: ~/.nvm/versions/node/v22.16.0/bin/node
  Yarn:
    version: 3.6.1
    path: ~/.nvm/versions/node/v22.16.0/bin/yarn
  npm:
    version: 10.9.2
    path: ~/.nvm/versions/node/v22.16.0/bin/npm
  Watchman:
    version: 2024.12.02.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.5
      - iOS 18.5
      - macOS 15.5
      - tvOS 18.5
      - visionOS 2.5
      - watchOS 11.5
  Android SDK: Not Found
IDEs:
  Android Studio: 2025.1 AI-251.25410.109.2511.13665796
  Xcode:
    version: 16.4/16F6
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 23.0.1
    path: /Users/dcorbin/.jenv/shims/javac
  Ruby:
    version: 3.4.1
    path: /Users/dcorbin/.rbenv/shims/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 19.0.0
    wanted: 19.0.0
  react-native:
    installed: 0.79.2
    wanted: 0.79.2
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

info React Native v0.80.1 is now available (your project is running on v0.79.2).
info Changelog: https://github.com/facebook/react-native/releases/tag/v0.80.1
info Diff: https://react-native-community.github.io/upgrade-helper/?from=0.79.2&to=0.80.1
info For more info, check out "https://reactnative.dev/docs/upgrading?os=macos".
Stacktrace or Logs
From my demo app, logging measurments for two dynamic text widths with 3 different parent setups.

 LOG  Measured abs-fixed  "100": 84px width
 LOG  Measured abs-fixed  "1000": 114.6669921875px width
 LOG  Measured abs-dyn  "100": 53.6669921875px width
 LOG  Measured abs-dyn  "1000": 53.6669921875px width
 LOG  Measured static  "100": 84px width
 LOG  Measured static  "1000": 114.6669921875px width

Of note, the "abs-dyn" lines shows how the widths for "100" and "1000" are equal because of the erroneous constraint.  In the GUI, the view gets colored red when the error is occurring.
MANDATORY Reproducer

https://github.com/dcorbin-bugs/overly-constrained-view

Screenshots and Videos
Image

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Erste Schritte

  1. Lies das ganze Issue und danach den Beitragsleitfaden des Projekts.
  2. Schreib ins Issue, dass du es übernimmst — das erspart doppelte Arbeit.
  3. Forke das Repository und arbeite in einem Branch.
  4. Öffne einen Pull Request, der die Issue-Nummer nennt.

Rechercherichtung

Beginne damit, den obligatorischen Reproducer unter github.com/dcorbin-bugs/overly-constrained-view auszuführen und die im Issue beschriebenen Messungen der absolut positionierten Elemente und des normalen Flows zu vergleichen. Als abgeschlossen gilt die Aufgabe, wenn dynamisch dimensionierte absolut positionierte Container den gemeldeten Breitenzwang nicht mehr auf untergeordnete Views übertragen und der Vergleich mit fester Breite weiterhin nachvollziehbar und durch die Verifizierung abgedeckt ist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.

Bewertung

Tech-Stack
ios, react-native
Bereich
mobile-dev
Issue-Typ
Bug
Schwierigkeit
4/5
Geschätzter Aufwand
3-5 Tage
Aktivitätsstatus
Veraltet
Klarheit
Größtenteils klar
Anfängerfreundlichkeit
42/100

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