Link XML formatting reference

This reference provides information on the correct formatting of link.xml files, including valid XML elements and attributes and usage examples.

Supported XML elements

The following XML elements are supported in link.xml files:

For example usages of all these elements, refer to Usage examples.

Supported XML attributes

For example usages of all these attributes, refer to Usage examples.

Usage examples

The following examples demonstrate valid usage of the supported XML elements and attributes.

Different ways to declare the root types of an assembly

The following examples illustrate the different ways that you can declare the root types of a project’s assemblies using a link.xml file:

<linker>
  <!--Preserve types and members in an assembly-->
  <assembly fullname="AssemblyName">
    <!--Preserve an entire type-->
    <type fullname="AssemblyName.TypeName" preserve="all"/>

    <!--No "preserve" attribute and no members specified means preserve all members-->
    <type fullname="AssemblyName.TypeName"/>

    <!--Preserve all fields on a type-->
    <type fullname="AssemblyName.TypeName" preserve="fields"/>

    <!--Preserve all methods on a type-->
    <type fullname="AssemblyName.TypeName" preserve="methods"/>

    <!--Preserve the type only-->
    <type fullname="AssemblyName.TypeName" preserve="nothing"/>

    <!--Preserving only specific members of a type-->
    <type fullname="AssemblyName.TypeName">
        
      <!--Fields-->
      <field signature="System.Int32 FieldName" />

      <!--Preserve a field by name rather than signature-->
      <field name="FieldName" />
      
      <!--Methods-->
      <method signature="System.Void MethodName()" />

      <!--Preserve a method with parameters-->
      <method signature="System.Void MethodName(System.Int32,System.String)" />

      <!--Preserve a method by name rather than signature-->
      <method name="MethodName" />

      <!--Properties-->

      <!--Preserve a property, its backing field (if present), 
          getter, and setter methods-->
      <property signature="System.Int32 PropertyName" />

      <property signature="System.Int32 PropertyName" accessors="all" />

      <!--Preserve a property, its backing field (if present), and getter method-->
      <property signature="System.Int32 PropertyName" accessors="get" />

      <!--Preserve a property, its backing field (if present), and setter method-->
      <property signature="System.Int32 PropertyName" accessors="set" />

      <!--Preserve a property by name rather than signature-->
      <property name="PropertyName" />

      <!--Events-->

      <!--Preserve an event, its backing field (if present), add, and remove methods-->
      <event signature="System.EventHandler EventName" />

      <!--Preserve an event by name rather than signature-->
      <event name="EventName" />

    </type>
  </assembly>
</linker>

Declare entire assemblies as roots

The following example shows how you can declare entire assemblies:

<!--Preserve an entire assembly-->
  <assembly fullname="AssemblyName" preserve="all"/>

  <!--No "preserve" attribute and no types specified means preserve all-->
  <assembly fullname="AssemblyName"/>

  <!--Fully qualified assembly name-->
  <assembly fullname="AssemblyName, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null">
    <type fullname="AssemblyName.Foo" preserve="all"/>
  </assembly>

  <!--Force an assembly to be processed for roots but don't explicitly preserve anything in particular. Useful when the assembly isn't referenced.-->
  <assembly fullname="AssemblyName" preserve="nothing"/>

Preserve nested or generic types

The following example shows how to preserve either nested or generic types:

<!--Examples with generics-->
    <type fullname="AssemblyName.G`1">

      <!--Preserve a field with generics in the signature-->
      <field signature="System.Collections.Generic.List`1<System.Int32> FieldName" />

      <field signature="System.Collections.Generic.List`1<T> FieldName" />

      <!--Preserve a method with generics in the signature-->
      <method signature="System.Void MethodName(System.Collections.Generic.List`1<System.Int32>)" />

      <!--Preserve an event with generics in the signature-->
      <event signature="System.EventHandler`1<System.EventArgs> EventName" />

    </type>

    <!--Preserve a nested type-->
    <type fullname="AssemblyName.H/Nested" preserve="all"/>

    <!--Preserve all fields of a type if the type is used.  If the type isn't used, it will be removed-->
    <type fullname="AssemblyName.I" preserve="fields" required="0"/>

    <!--Preserve all methods of a type if the type is used. If the type isn't used, it will be removed-->
    <type fullname="AssemblyName.J" preserve="methods" required="0"/>

    <!--Preserve all types in a namespace-->
    <type fullname="AssemblyName.SomeNamespace*" />

    <!--Preserve all types with a common prefix in their name-->
    <type fullname="Prefix*" />

Ignore a missing assembly

Use the ignoreIfMissing attribute on the <assembly> element if you need to declare preservations for an assembly that doesn’t exist during all Player builds:

<linker>
  <assembly fullname="Foo" ignoreIfMissing="1">
    <type name="TypeName"/>
  </assembly>
</linker>

Ignore an unreferenced assembly

Use the ignoreIfUnreferenced attribute on the <assembly> element to preserve the entities in an assembly only when at least one type is referenced in another assembly:

<linker>
  <assembly fullname="Bar" ignoreIfUnreferenced="1">
    <type name="TypeName"/>
  </assembly>
</linker>

Windows Runtime Metadata assembly

You must use the windowsruntime attribute on the <assembly> element whenever you define preservations for a Windows Runtime Metadata (.winmd) assembly:

<linker>
  <assembly fullname="Windows" windowsruntime="true">
    <type name="TypeName"/>
 </assembly>
</linker>

Feature exclusions

The mscorlib.xml file embedded in mscorlib.dll uses this attribute, but you can use it in any link.xml file when appropriate.

At the High stripping level, the Unity linker excludes preservations for features that aren’t supported based on the settings for the current build:

1. remoting — Excluded when targeting the IL2CPPA Unity-developed scripting back-end which you can use as an alternative to Mono when building projects for some platforms. More info
   See in Glossary scripting backendA framework that powers scripting in Unity. Unity supports three different scripting backends depending on target platform: Mono, .NET and IL2CPP. Universal Windows Platform, however, supports only two: .NET and IL2CPP. More info
   See in Glossary.
2. sre — Excluded when targeting the IL2CPP scripting backend.
3. com — Excluded when targeting platforms that don’t support COM.

For example, the following link.xml file preserves one method of a type on platforms that support COM, and one method on all platforms:

<linker>

    <assembly fullname="Foo">

        <type fullname="Type1">

            <!--Preserve FeatureOne on platforms that support COM-->

            <method signature="System.Void FeatureOne()" feature="com"/>

            <!--Preserve FeatureTwo on all platforms-->

            <method signature="System.Void FeatureTwo()"/>

        </type>

    </assembly>

</linker>

Additional resources

• Managed code stripping and the Unity linker
• Configure managed code stripping
• Preserving code using annotations
• Unity linker marking rules reference
• IUnityLinkerProcessor.GenerateAdditionalLinkXmlFile