Microsoft.XmlSerializer.Generator does not support incremental build

[jeffreyrivor]

Description

After adding XML serializer generation to an SDK-style project, the serialization DLL is always rebuilt even when incremental build skips the CoreCompile target because it has detected that no code has changed.

• Run dotnet build which materializes the intermediate CS/DLL/PDB files (in obj) and copies output DLL/PDB files (in bin) for the serializer
• Run dotnet build again, core compilation is skipped so no file timestamps are changed, but the serialization intermediate CS/DLL/PDB files are recreated with new timestamps which are copied to output (bin)
  • Additionally, the generated CS file is slightly different each time in the generated XmlSerializationReader1.InitIDs() method which appears to be non-deterministic. I'm not sure if being source-level deterministic on generated code is required to consider the overall build deterministic.

Configuration

.NET Core SDK 5.0.203 on Windows 10 x64

<Project Sdk="Microsoft.NET.Sdk">
	<PropertyGroup>
		<TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
	</PropertyGroup>

	<ItemGroup>
		<PackageReference Include="Microsoft.XmlSerializer.Generator" Version="5.0.0" PrivateAssets="All" />
	</ItemGroup>

	<ItemGroup>
		<DotNetCliToolReference Include="Microsoft.XmlSerializer.Generator" Version="5.0.0" />
	</ItemGroup>
</Project>

Regression?

No, it seems like incremental build support was not part of the porting of .NET Framework SGen MSBuild task to Microsoft.XmlSerializers.Generator .NET Core tool.

Other information

It seems like more of the MSBuild logic for Compile (e.g. GenerateAssemblyInfo for #49003 and the logic for Inputs on the CoreCompile target) is needed to bring the serialization generator more in line with the features (assembly attributes, incremental build, deterministic build) of the normal compilation flow.

[Latency]

  <ItemGroup Condition="'$(TargetFramework)'=='net6.0-windows'">
    <PackageReference Include="Microsoft.XmlSerializer.Generator" Version="6.0.0-preview.3.21201.4" PrivateAssets="All" />
    <DotNetCliToolReference Include="Microsoft.XmlSerializer.Generator" Version="6.0.0-preview.3.21201.4" />
  </ItemGroup>

  <PropertyGroup Condition="'$(TargetFramework)'=='net6.0-windows'">
    <GenerateSerializationAssemblies>On</GenerateSerializationAssemblies>
  </PropertyGroup>

Error: An attempt was made to load an assembly with an incorrect format: C:\Program Files\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.3.21201.4\ref\net6.0\Microsoft.CSharp.dll.

---

Remove the [GenerateSerializationAssemblies] or set to 'Auto' by default yields..... results below.

---

Compile
Run

var s = new XmlSerializer(objType);

System.IO.FileNotFoundException: 'Could not load file or assembly '~\bin\Debug\net6.0-windows\ [assemblyName].XmlSerializers.dll'. The system cannot find the file specified.'

[jeffreyrivor]

  <ItemGroup Condition="'$(TargetFramework)'=='net6.0-windows'">
    <PackageReference Include="Microsoft.XmlSerializer.Generator" Version="6.0.0-preview.3.21201.4" PrivateAssets="All" />
    <DotNetCliToolReference Include="Microsoft.XmlSerializer.Generator" Version="6.0.0-preview.3.21201.4" />
  </ItemGroup>

  <PropertyGroup Condition="'$(TargetFramework)'=='net6.0-windows'">
    <GenerateSerializationAssemblies>On</GenerateSerializationAssemblies>
  </PropertyGroup>

Error: An attempt was made to load an assembly with an incorrect format: C:\Program Files\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.3.21201.4\ref\net6.0\Microsoft.CSharp.dll.

Remove the [GenerateSerializationAssemblies] or set to 'Auto' by default yields..... results below.

Compile
Run

var s = new XmlSerializer(objType);

System.IO.FileNotFoundException: 'Could not load file or assembly '~\bin\Debug\net6.0-windows\ [assemblyName].XmlSerializers.dll'. The system cannot find the file specified.'

The SGen task that is invoked by setting GenerateSerializationAssemblies is only supported for .NET Framework (see dotnet/sdk#2456). The Microsoft.XmlSerializer.Generator dotnet tool runs without setting GenerateSerializationAssemblies. That said, I'm surprised that MSBuild didn't throw a more friendly error to indicate this (see dotnet/msbuild#3583).

[chm-tm]

Work around:

• Author a custom .targets file in your build where you copy the original GenerateSerializationAssembly to.
• Add Inputs="@(ReferencePath);@(IntermediateAssembly)" and Outputs="$(_SerializerDllIntermediateFolder) to the GenerateSerializationAssembly target.
• Import your custom .targets file in your project by using the CustomAfterMicrosoftCSharpTargets property. This way, our target can overwrite the original target.

[StephenMolloy]

Fixed in 7.0-rc1 by #73550