Assembly validation

Similar to package validation, assembly validation tooling allows you, as a library developer, to validate that your assemblies are consistent and well formed. Use assembly validation instead of package validation when your app isn't packable.

Assembly validation provides the following checks:

• Validates that there are no breaking changes across versions.
• Validates that the assembly has the same set of public APIs for all the different runtime-specific implementations.
• Catches any applicability holes.

You can run assembly validation either as an MSBuild task or using the Microsoft.DotNet.ApiCompat.Tool global tool.

Enable MSBuild task

You enable assembly validation in your .NET project by setting the ApiCompatValidateAssemblies property to true and specifying the path to the contract (baseline) assembly. You must also add a package reference to Microsoft.DotNet.ApiCompat.Task. (The targets files in that package aren't part of the .NET SDK.)

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFrameworks>net8.0</TargetFrameworks>
    <ApiCompatValidateAssemblies>true</ApiCompatValidateAssemblies>
    <ApiCompatContractAssembly>[Path to contract assembly]</ApiCompatContractAssembly>
    <IsPackable>false</IsPackable>
  </PropertyGroup>

  <ItemGroup Condition="'$(ApiCompatValidateAssemblies)' == 'true'">
    <PackageReference Include="Microsoft.DotNet.ApiCompat.Task" Version="8.0.100" PrivateAssets="all" IsImplicitlyDefined="true" />
  </ItemGroup>

</Project>

Assembly validation runs either in the outer build for multi-targeting projects (after the DispatchToInnerBuilds target) or in the inner build for a single-targeting project (as part of the PrepareForRun target). It's also fully incremental, meaning the comparison is only triggered if the inputs or outputs have changed.

Example

1. Create and build a C# class library named "ValidateMe" that contains the following simple interface:

   namespace ValidateMe;
   
   public interface IAnimal
   {
       string Name { get; }
       //string Sound { get; }
   }
   

2. Rename the output assembly to "ValidateMeV1.dll".

3. Add the Sound property to the interface by uncommenting that line of code.

4. Add the ApiCompatValidateAssemblies and ApiCompatContractAssembly properties and the "Microsoft.DotNet.ApiCompat.Task" package reference to your project file. Also increment the version of your assembly to "2.0.0".

   <PropertyGroup>
     <OutputType>Library</OutputType>
     <TargetFrameworks>net8.0</TargetFrameworks>
     <ApiCompatValidateAssemblies>true</ApiCompatValidateAssemblies>
     <ApiCompatContractAssembly>$(OutDir)bin\Release\net8.0\ValidateMeV1.dll</ApiCompatContractAssembly>
     <IsPackable>false</IsPackable>
     <Version>2.0.0</Version>
   </PropertyGroup>
   
   <ItemGroup Condition="'$(ApiCompatValidateAssemblies)' == 'true'">
      <PackageReference Include="Microsoft.DotNet.ApiCompat.Task" Version="8.0.100" PrivateAssets="all" IsImplicitlyDefined="true" />
   </ItemGroup>
   

5. Rebuild your class library.

   The build fails with the following errors:

   C:\Users\me\.nuget\packages\microsoft.dotnet.apicompat.task\8.0.100\build\Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error : API compatibility errors between 'bin\Release\net8.0\ValidateMeV1.dll' (left) and 'C:\Users\me\source\repos\ValidateMe\bin\Release\net8.0\ValidateMe.dll' (right):
   1>C:\Users\me\.nuget\packages\microsoft.dotnet.apicompat.task\8.0.100\build\Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error CP0006: Cannot add interface member 'string ValidateMe.IAnimal.Sound' to C:\Users\me\source\repos\ValidateMe\bin\Release\net8.0\ValidateMe.dll because it does not exist on bin\Release\net8.0\ValidateMeV1.dll
   1>C:\Users\me\.nuget\packages\microsoft.dotnet.apicompat.task\8.0.100\build\Microsoft.DotNet.ApiCompat.ValidateAssemblies.Common.targets(16,5): error : API breaking changes found. If those are intentional, the APICompat suppression file can be updated by rebuilding with '/p:ApiCompatGenerateSuppressionFile=true'
   

Suppress compatibility warnings

For information about suppressing compatibility warnings, see How to suppress.