Overview

Assembly trimming removes unused parts of libraries from the application package, thereby reducing size.

Trimming is only available for self-contained deployments.

Considerations

Trimming has known incompatibilities. See https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/incompatibilities

Enabling

To enable trimming:

1. Enable trimming in the project file:
   SomeProject.csproj

   <PropertyGroup>
       <PublishTrimmed>true</PublishTrimmed>
   </PropertyGroup>
   

2. Publish the app as self-contained
   • Via CLI:

   dotnet publish -r <RUNTIME-ID>
   

   Note: The -p:PublishTrimmed=true switch is not required if trimming is enabled in the project file.
   • Via Visual Studio:
     1. Right-click project in Solution Explorer > Publish
     2. More actions > Edit
     3. Profile settings dialog > Set the Deployment mode > Set the Target runtime > Check Trim unused code > Save
     4. Publish

Trimming Options

The following MSBuild properties and items change trimming behavior.
Note: ILLink is the name of the underlying tool that implements trimming.

Trim Mode

The default trim mode in .NET 7 is full. This trims all assemblies:

<TrimMode>partial</TrimMode>

Set trimmable assemblies

If the above is set to partial, set this to opt-in individual assemblies:

<ItemGroup>
    <TrimmableAssembly Include="ASSEMBLY-NAME" />
</ItemGroup>

Root assemblies

Assemblies that are not trimmed is considered “rooted.” Additional assemblies can be rooted:

<ItemGroup>
    <TrimmerRootAssembly Include="ASSEMBLY-NAME" />
</ItemGroup>

Analysis warnings

• SuppressTrimAnalysisWarnings is boolean if trim analysis warnings should be enabled. Default = false.
• EnableTrimAnalyzer is boolean to enable a limited set of Roslyn analyzers. Default = true.
• ILLinkTreatWarningsAsErrors is boolean to treat warnings as errors.
• TrimmerSingleWarn is boolean to show detailed errors instead of collapsing them into a single warning per assembly.
• TrimmerRemoveSymbols is boolean to remove symbols (such as PDBs) from the trimmed application.

Framework Features Automatically Disabled When Trimming

See: https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/trimming-options?pivots=dotnet-7-0#framework-features-disabled-when-trimming

Preparing a Library for Trimming

See https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/prepare-libraries-for-trimming

Trimming Framework Library Features

See: https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/trimming-options?pivots=dotnet-7-0#trimming-framework-library-features