Unity linker marking rules reference

When the Unity linker performs its static analysis, it follows sets of rules to determine which parts of the CIL bytecode to mark as necessary for the build:

Root marking rules determine how the Unity linker identifies and preserves top-level assemblies in the build.
Dependency marking rules determine how the Unity linker identifies and preserves any code that the root assemblies depend on.

The configured managed stripping level changes the set of rules that the Unity linker uses. The following sections describe the marking rules at each managed stripping level.

Root marking rules

The following table describes how the Unity linker identifies the top-level types in an assembly for different assembly types and managed stripping levels:

Assembly type	Root marking rules at managed stripping levels
.NET Class & Platform SDK and UnityEngine Assemblies	Minimal and Low: Precautionary preservations Minimal, Low, Medium and High: Preservations defined in any `link.xml` file
Assemblies with types referenced in a scene	Minimal and Low: All types and members in the assembly Medium and High: All methods which have the `[RuntimeInitializeOnLoadMethod]` or `[Preserve]` attribute. Preservations defined in any `link.xml` file All types derived from MonoBehaviour and ScriptableObject in precompiled, package, Unity Script or assembly definition assemblies.
All other	Minimal: All types and members in the assembly Low and Medium: All public types and public members of those types Medium and High: All methods which have the `[RuntimeInitializeOnLoadMethod]` or `[Preserve]` attribute. Preservations defined in any `link.xml` file All types derived from MonoBehaviour and ScriptableObject in precompiled, package, Unity Script or assembly definition assemblies.
Test	Minimal, Low, Medium and High: Any methods with the `[UnityTest]` attribute and any methods annotated with an Attribute defined in the NUnit.Framework.

Dependency marking rules

After the Unity linker identifies the roots in an assembly, it needs to identify any code that those roots depend on. The following table describes how the Unity linker identifies dependencies of root types in an assembly at different managed stripping levels:

Rule target	Dependency marking rules at managed stripping levels
MonoBehaviour	Minimal, Low, Medium and High: The Unity linker marks all members of a MonoBehavior type when it marks the type
ScriptableObject	Minimal, Low, Medium and High: The Unity linker marks all members of a ScriptableObject type when it marks the type
Attributes	Minimal and Low: When the Unity linker marks an assembly, type or other code structure, it also marks all attributes of those structures. Medium and High: When the Unity linker marks an assembly, type or other code structure, it only marks attributes of those structures if the attribute type is also marked.
Debugging Attributes	Minimal and Low: When script debugging is enabled, the Unity linker marks all members that have the `[DebuggerDisplay]` attribute, even when there isn’t a code path that uses those members. Medium and High: The Unity linker always removes debugging attributes such as `DebuggerDisplayAttribute` and `DebuggerTypeProxyAttribute`.
.NET Facade Class Library	Minimal, Low, Medium and High: Removes facade assemblies since they aren’t necessary at runtime.

Additional resources

Link XML formatting reference

Scripting backends

手册

Unity linker marking rules reference

Root marking rules

Dependency marking rules

Additional resources