Documentation

Unity Engine

User Manual

Script Reference

Unity Engine

How code stripping affects content

Understand how your managed code stripping configuration can affect content builds and how to preserve code your content depends on.
Read time 3 minutesLast updated 13 days ago
When you build a Player in Unity, the UnityLinker process runs to reduce the size of the assemblies by removing unused types. This process can strip the following:
  • Entire C# Unity objects such as 
    MonoBehaviour
    and 
    ScriptableObject
    instances. Unity can strip these from core Unity assemblies like 
    UnityEngine.dll
    and 
    Unity.dll
    , but preserves them in custom assemblies once those assemblies are marked as used.
  • Regular C# structures and classes.
  • Portions of classes (for example, methods that aren't used).
  • Entire Unity modules, such as AI or Physics, if no type from that module is referenced.
The affect that code stripping has on content appears in the Player as null reference exceptions, missing type errors, or crashes. Additionally, AssetBundle or Addressables content-only build can't use types that have been stripped out of a Player build.
You can use the Build Report Inspector's Stripping tab to inspect which modules and types have been preserved in a Player build.
You can prevent the linker from stripping code in the following circumstances:

Prevent code stripping of types used in AssetBundles

Unity might strip a Unity object type that's present in AssetBundles, but not in any scene or asset included in a Player build. This means that content from the AssetBundle might work when testing in Play mode, or on builds with minimal code stripping, but errors or crashes occur in a Player built with code stripping enabled.
To resolve this, you can create a custom build script that directly includes the AssetBundle's manifest file, as follows:
  1. Build the AssetBundle before building the Player. The output folder includes one 
    .manifest
    file for each AssetBundle, and a root 
    .manifest
    file with the same name as the output folder.
  2. Pass the path of the root 
    .manifest
    file into the Player build process with the 
    BuildPipeline.BuildPlayer
     API.
For more information, refer to AssetBundle file format reference and 
BuildPlayerOptions.assetBundleManifestPath
.
You can also use the Preserve attribute, or manually author a 
link.xml
 file in your project, to further influence the code stripping behavior.

Preventing stripping of types used in Addressables

If a type of Unity object is present in content built with Addressables, but not in any scene or asset built into the Player, then Unity might strip that type.
Addressables automatically generates a 
link.xml
 file inside the 
Library/com.unity.addressables
folder describing types used in the content. The Player build takes this 
link.xml
file into account, provided the Addressables content has been built before, or at the same time as, the Player build.
You can also use the Preserve attribute, or manually author a 
link.xml
 file in your project, to further influence the code stripping behavior.

Preventing module stripping

You can't use a 
link.xml
file to prevent entire Unity modules (for example AI or Physics) from being stripped.
If you need to use types from a module in an Addressables build, make sure the Player build includes some content that references that module. For example, to keep the Physics module, add a component such as a Rigidbody or Collider to a GameObject in a scene included in your build. This creates a dependency that the Player build process recognizes, and preserves the module.

Script-only builds

Player builds record the used types in a 
ScriptsOnlyCache.yaml
file inside the 
Library/PlayerDataCache
folder, which you can look at to diagnose any code stripping issues. This file is used to support the Incremental build pipeline which can reuse the content from a previous Player build. In that case the Player build passes the cached type usage from that file to the Unity linker.
Note
The 
ScriptsOnlyCache.yaml
file uses an internal format that might change in future Unity versions. To control code stripping, use 
link.xml
files in your project instead of modifying this file directly.

Additional resources