[BUG] Coverlet.Collector produces empty report when Mediator.SourceGenerator is referenced

[alex-zyl]

Describe the bug
Please share a clear and concise description of the problem.

To Reproduce

1. Create WebAPI and UnitTest projects from template.
2. Add Mediator packages to WebAPI project

<ItemGroup>
  <PackageReference Include="Mediator.Abstractions" Version="3.0.0-preview.27" />
  <PackageReference Include="Mediator.SourceGenerator" Version="3.0.0-preview.27" >
  <PrivateAssets>all</PrivateAssets>
    <IncludeAssets>runtime; build; native; contentfiles; analyzers;</IncludeAssets>
  </PackageReference>
</ItemGroup>

3. Run tests

dotnet test .\TestProject.sln --configuration Debug --collect:"XPlat Code Coverage" --diag:log.txt

Expected behavior
Coverage report includes types from analyzed project.

Actual behavior
Coverage report is empty.

<?xml version="1.0" encoding="utf-8"?>
<coverage line-rate="0" branch-rate="0" version="1.9" timestamp="1734109700" lines-covered="0" lines-valid="0" branches-covered="0" branches-valid="0">
  <sources />
  <packages />
</coverage>

Configuration (please complete the following information):
Please provide more information on your .NET configuration:
* Which coverlet package and version was used?
6.0.0
* Which version of .NET is the code running on?
net8.0
* What OS and version, and what distro if applicable?
Win11
* What is the architecture (x64, x86, ARM, ARM64)?
x64
* Do you know whether it is specific to that configuration?
No

Additional context
log.datacollector contains the following exception

TpTrace Information: 0 : 35584, 1, 2024/12/13, 18:07:37.009, 629740483105, datacollector.dll, AssemblyResolver.OnResolve: Resolved assembly: Microsoft.DotNet.PlatformAbstractions, from path: C:\Users\admin\.nuget\packages\coverlet.collector\6.0.0\build\netstandard1.0\Microsoft.DotNet.PlatformAbstractions.dll
TpTrace Verbose: 0 : 35584, 1, 2024/12/13, 18:07:37.012, 629740517319, datacollector.dll, [coverlet]AspNetCoreSharedFrameworkResolver search paths:
TpTrace Verbose: 0 : 35584, 1, 2024/12/13, 18:07:37.012, 629740517703, datacollector.dll, [coverlet]C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All\9.0.0
TpTrace Verbose: 0 : 35584, 1, 2024/12/13, 18:07:37.012, 629740517868, datacollector.dll, [coverlet]C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App\9.0.0
TpTrace Verbose: 0 : 35584, 1, 2024/12/13, 18:07:37.013, 629740524572, datacollector.dll, [coverlet]Loading D:\Projects\Sandbox\Testcoverage\Testsnet8\bin\Debug\net8.0\testsnet8.deps.json
TpTrace Warning: 0 : 35584, 1, 2024/12/13, 18:07:37.017, 629740570341, datacollector.dll, [coverlet]Unable to instrument module: D:\Projects\Sandbox\Testcoverage\Testsnet8\bin\Debug\net8.0\ProjNet8.dll
Coverlet.Core.Exceptions.CecilAssemblyResolutionException: AssemblyResolutionException for 'Microsoft.Extensions.DependencyInjection.Abstractions, Version=8.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'. Try to add <PreserveCompilationContext>true</PreserveCompilationContext> to test projects </PropertyGroup> or pass '/p:CopyLocalLockFileAssemblies=true' option to the 'dotnet test' command-line
 ---> Mono.Cecil.AssemblyResolutionException: Failed to resolve assembly: 'Microsoft.Extensions.DependencyInjection.Abstractions, Version=8.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'
   --- End of inner exception stack trace ---
   at Coverlet.Core.Instrumentation.NetstandardAwareAssemblyResolver.TryWithCustomResolverOnDotNetCore(AssemblyNameReference name) in /_/src/coverlet.core/Instrumentation/CecilAssemblyResolver.cs:line 215
   at Coverlet.Core.Instrumentation.NetstandardAwareAssemblyResolver.Resolve(AssemblyNameReference name) in /_/src/coverlet.core/Instrumentation/CecilAssemblyResolver.cs:line 127
   at Mono.Cecil.MetadataResolver.Resolve(TypeReference type)
   at Mono.Cecil.ModuleDefinition.Resolve(TypeReference type)
   at Mono.Cecil.TypeReference.Resolve()
   at Mono.Cecil.Mixin.CheckedResolve(TypeReference self)
   at Mono.Cecil.MetadataBuilder.GetConstantType(TypeReference constant_type, Object constant)
   at Mono.Cecil.MetadataBuilder.AddConstant(IConstantProvider owner, TypeReference type)
   at Mono.Cecil.MetadataBuilder.AddField(FieldDefinition field)
   at Mono.Cecil.MetadataBuilder.AddFields(TypeDefinition type)
   at Mono.Cecil.MetadataBuilder.AddType(TypeDefinition type)
   at Mono.Cecil.MetadataBuilder.AddTypes()
   at Mono.Cecil.MetadataBuilder.BuildTypes()
   at Mono.Cecil.MetadataBuilder.BuildModule()
   at Mono.Cecil.MetadataBuilder.BuildMetadata()
   at Mono.Cecil.ModuleWriter.<>c.<BuildMetadata>b__2_0(MetadataBuilder builder, MetadataReader _)
   at Mono.Cecil.ModuleDefinition.Read[TItem,TRet](TItem item, Func`3 read)
   at Mono.Cecil.ModuleWriter.BuildMetadata(ModuleDefinition module, MetadataBuilder metadata)
   at Mono.Cecil.ModuleWriter.Write(ModuleDefinition module, Disposable`1 stream, WriterParameters parameters)
   at Mono.Cecil.ModuleWriter.WriteModule(ModuleDefinition module, Disposable`1 stream, WriterParameters parameters)
   at Mono.Cecil.ModuleDefinition.Write(Stream stream, WriterParameters parameters)
   at Coverlet.Core.Instrumentation.Instrumenter.InstrumentModule() in /_/src/coverlet.core/Instrumentation/Instrumenter.cs:line 333
   at Coverlet.Core.Instrumentation.Instrumenter.Instrument() in /_/src/coverlet.core/Instrumentation/Instrumenter.cs:line 149
   at Coverlet.Core.Coverage.PrepareModules() in /_/src/coverlet.core/Coverage.cs:line 135

Including <PreserveCompilationContext>true</PreserveCompilationContext> and CopyLocalLockFileAssemblies do not make any effect.

Workaround

1. Add <PreserveCompilationContext>true</PreserveCompilationContext>
2. Copy dependencies via AfterBuild task

  <Target Name="CopyMediatorSourceGenDeps" AfterTargets="Build">
    <ItemGroup>
      <ResolvedFiles Include="$(OutputPath)/refs/Microsoft.Extensions.DependencyInjection.Abstractions.dll" />
    </ItemGroup>
    <Copy SourceFiles="@(ResolvedFiles)" DestinationFolder="$(OutputPath)" />
  </Target>

[Bertk]

Thanks a lot for reporting this issue. The current coverlet.collector version 6.0.3 targets netstandard2.0 only. This issue will be solved in the next major version.

[alex-zyl]

Thanks for heads up @Bertk
Can't NetstandardAwareAssemblyResolver just be updated to try to lookup an assembly in refs folder if not found in main directory?

[Bertk]

Please you please try to use a self contained test executable. This might resolve the dependency problem.

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net8.0-windows</TargetFramework>
    <PreserveCompilationContext>true</PreserveCompilationContext>
    <SelfContained>true</SelfContained>
    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
  </PropertyGroup>