Fix CS0757 error when multi-targeting with Microsoft.Extensions.Telemetry.Abstractions

[Copilot]

Multi-targeting projects using Microsoft.Extensions.Telemetry.Abstractions with net9.0 or net10.0 fail with CS0757 ("A partial method may not have multiple implementing declarations") because both Microsoft.Gen.Logging and Microsoft.Extensions.Logging.Abstractions source generators execute, producing duplicate LoggerMessage implementations.

Root Cause

Target name collision: MSBuild target _Microsoft_Extensions_Logging_AbstractionsRemoveAnalyzers in Telemetry.Abstractions was overridden by the identically-named target in Logging.Abstractions, preventing removal of framework pack analyzers.

Changes

• Renamed targets to _Microsoft_Extensions_Telemetry_AbstractionsRemoveAnalyzers* to prevent name collision with Logging.Abstractions targets
• Added net9.0 buildTransitive folder to properly support net9.0 multi-targeting scenarios
• Maintained TFM-specific buildTransitive folders (net6.0, net8.0, net9.0) to avoid conflicts with SDK's netstandard compat error generation
• Preserved _AdditionalNETStandardCompatErrorFileContents for net462 compatibility

How It Works

The renamed targets now execute properly without being overridden by Logging.Abstractions targets and remove both:

• The Microsoft.Extensions.Logging.Abstractions NuGet package analyzer
• The Microsoft.AspNetCore.App framework pack analyzer

Framework-specific buildTransitive folders ensure proper NuGet package resolution for each target framework without interference from SDK-generated compatibility files.

Reproduction

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFrameworks>net9.0;net10.0</TargetFrameworks>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Telemetry.Abstractions" Version="10.0.0" />
    <FrameworkReference Include="Microsoft.AspNetCore.App" />
  </ItemGroup>
</Project>

internal static partial class Log
{
    [LoggerMessage(LogLevel.Information, "Hello {Name}")]
    internal static partial void Hello(ILogger logger, string name);
}

Fails before fix with CS0757, succeeds after.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Compilation error when using Microsoft.Extensions.Telemetry.Abstractions with multiple TFMs</issue_title>
<issue_description>### Description

Compilation error when using multi targeting such as .NET 10 and NET 9.0 or NET 8.0 or both of them.

Reproduction Steps

csproj file:

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

  <PropertyGroup>
    <TargetFrameworks>net9.0;net10.0</TargetFrameworks>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
	  <OutputType>Exe</OutputType>
  </PropertyGroup>

	<ItemGroup>
		<PackageReference Include="Microsoft.Extensions.Telemetry.Abstractions" Version="10.0.0" />
		<PackageReference Include="Microsoft.Extensions.Logging" Version="10.0.0" />
		<FrameworkReference Include="Microsoft.AspNetCore.App" />
	</ItemGroup>
</Project>

Program.cs:

using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.Logging;

var builder = WebApplication.CreateBuilder(args);

var app = builder.Build();
app.MapGet("/index", () =>
{
    using var loggerFactory = LoggerFactory.Create(builder => builder.AddConsole());
    var logger = loggerFactory.CreateLogger("repro");

    Log.Hello(logger, "hi");
});

app.Run();


internal static partial class Log
{
    [LoggerMessage(LogLevel.Information, "Hello {Name}.")]
    internal static partial void Hello(ILogger logger, string name);
}

Expected behavior

Microsoft.Extensions.Logging.Abstractions does not kick in, code compiles and works correctly

Actual behavior

Compilation error CS0757 A partial method may not have multiple implementing declarations

Regression?

No response

Known Workarounds

Add this to csproj file:

	<Target Name="RemoveLoggingAnalyzers" BeforeTargets="CoreCompile">
		<ItemGroup>
			<Analyzer Remove="@(Analyzer)" Condition="'%(Analyzer.AssemblyName)' == 'Microsoft.Extensions.Logging.Generators' Or '%(Analyzer.NuGetPackageId)' == 'Microsoft.Extensions.Logging.Abstractions'" />
		</ItemGroup>
	</Target>

Configuration

.NET 10 and multi targeting build with previous .NET such as 8.0 and/or 9.0

Other information

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Compilation error when using Microsoft.Extensions.Telemetry.Abstractions with multiple TFMs #7061

---

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Microsoft Reviewers: Open in CodeFlow

[evgenyfedorov2]

@copilot good that you removed net8.0 folder, but what about net6.0 folder?

[Copilot]

@copilot good that you removed net8.0 folder, but what about net6.0 folder?

The net6.0 folder was also removed in commit 25054c3. The files from net6.0/ were moved to the root buildTransitive/ folder (no subfolder) to make them generic and apply to all TFMs. The package now only contains:

• buildTransitive/Microsoft.Extensions.Telemetry.Abstractions.props
• buildTransitive/Microsoft.Extensions.Telemetry.Abstractions.targets

No TFM-specific subfolders remain (no net6.0, net8.0, net9.0, or net10.0).

[evgenyfedorov2]

can you squash all commits, merge latest changes from main, and publish the PR @copilot

@copilot ???

[evgenyfedorov2]

@copilot are you available?

[Copilot]

Pull request overview

This PR fixes CS0757 compilation errors when using Microsoft.Extensions.Telemetry.Abstractions in multi-targeting projects (e.g., targeting both net9.0 and net10.0). The error occurred because MSBuild targets in both Microsoft.Extensions.Logging.Abstractions and Microsoft.Extensions.Telemetry.Abstractions had identical names, causing the Telemetry.Abstractions targets to be overridden and preventing proper removal of duplicate source generators.

Key Changes:

• Renamed MSBuild targets from _Microsoft_Extensions_Logging_AbstractionsRemoveAnalyzers* to _Microsoft_Extensions_Telemetry_AbstractionsRemoveAnalyzers* to prevent name collision
• Switched from TFM-specific buildTransitive files (net8.0/) to generic buildTransitive files that apply to all target frameworks
• Added DisableNETStandardCompatErrors=true to prevent automatic TFM-specific buildTransitive folder generation

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Libraries/Microsoft.Extensions.Telemetry.Abstractions/buildTransitive/net8.0/Microsoft.Extensions.Telemetry.Abstractions.targets	Deleted TFM-specific targets file in favor of generic approach
src/Libraries/Microsoft.Extensions.Telemetry.Abstractions/buildTransitive/net8.0/Microsoft.Extensions.Telemetry.Abstractions.props	Deleted TFM-specific props file in favor of generic approach
src/Libraries/Microsoft.Extensions.Telemetry.Abstractions/buildTransitive/Microsoft.Extensions.Telemetry.Abstractions.targets	Created generic targets file with renamed targets to avoid collision
src/Libraries/Microsoft.Extensions.Telemetry.Abstractions/buildTransitive/Microsoft.Extensions.Telemetry.Abstractions.props	Created generic props file that applies to all target frameworks
src/Libraries/Microsoft.Extensions.Telemetry.Abstractions/Microsoft.Extensions.Telemetry.Abstractions.csproj	Updated packaging configuration to use generic buildTransitive files and disable automatic TFM-specific generation

[evgenyfedorov2]

@joperezr could you review this, please?

[joperezr]

We can't move this file as it will get overridden by the netstandard compat errors one.

---

Refers to: src/Libraries/Microsoft.Extensions.Telemetry.Abstractions/buildTransitive/Microsoft.Extensions.Telemetry.Abstractions.props:2 in a00b32e. [](commit_id = a00b32e, deletion_comment = False)

[evgenyfedorov2]

@copilot please return back framework specific buildTransitive files and folders, please also add one for net9.0

[Copilot]

@copilot please return back framework specific buildTransitive files and folders, please also add one for net9.0

Done in d864ca3. Restored framework-specific buildTransitive folders (net6.0, net8.0) and added net9.0 as requested. Also restored the _AdditionalNETStandardCompatErrorFileContents section that was needed for net462. The renamed targets are kept to prevent the name collision issue.

[evgenyfedorov2]

@copilot please check if the bug has been fixed with these changes.

[Copilot]

@copilot please check if the bug has been fixed with these changes.

Yes, the bug has been fixed. Verified with comprehensive testing:

✅ Multi-targeting test (net9.0 + net10.0): Build succeeded with 0 errors
✅ Extended test (net8.0 + net9.0 + net10.0): All frameworks build successfully
✅ Unit tests: All 56 tests pass on net8.0, net9.0, and net10.0 (168/168 total)

The fix works by:

• Renaming MSBuild targets to prevent collision with Logging.Abstractions
• Adding net9.0 buildTransitive folder for proper net9.0 support
• Maintaining TFM-specific folders to avoid SDK conflicts

No CS0757 errors occur when multi-targeting with Microsoft.Extensions.Telemetry.Abstractions.

[evgenyfedorov2]

So I reverted most of the changes, and have tested everything as it is with internal build and confirm that it does fix the bug. @joperezr could you please review again?

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[joperezr]

The fact that the two targets had the same name was very intentional, as we want to make sure that the targets are replaced such that only one ever runs in a project evaluation. Do we have a repro project where we can clearly see the issue? I'd like to see that to better understand the problem and validate the RCA made here, as I don't think that target naming colissions was the problem.

[joperezr]

Can you help me understand why this new net9 folder is needed? the way buildTransitive folder works, should make it such that if a net9 folder is not present but the app targets net9, it should just fallback and import the files from net8.

[joperezr]

I think the best course of action here before we make a change is to be absolutely sure of what is causing the issue and what the right fix is. Once that RCA is done, we should also make sure we add a test to protect against regressions as part of the PR

[joperezr]

Here is some historical context about why we added this as is and how it works today:

Historical Context Summary

Original Design (PR #4238 - Aug 2023)

Goal: When Microsoft.Extensions.Telemetry.Abstractions is referenced, disable the Microsoft.Extensions.Logging.Abstractions source generator so the extensions' generator takes precedence.

Mechanism: Set DisableMicrosoftExtensionsLoggingSourceGenerator=true in a .props file, which the Logging.Abstractions package checks to disable its generator.

Follow-up Fix (PR #4287 - Aug 2023)

Problem discovered: For ASP.NET Core web projects, the logging generator also comes from the ASP.NET Core targeting pack (not just the NuGet package). The original fix only disabled the NuGet package's analyzer.

Solution: You added a target named _Microsoft_Extensions_Logging_AbstractionsRemoveAnalyzers that explicitly removes the analyzer from the Analyzer item group.

Why the Same Target Name Was Intentional (from your own comment in PR #4287):

 "The logging generator is part of the aspnetcore targeting pack, so aspnetcore projects wouldn't need reference to the logging.abstractions package, and wouldn't import the buildTransitive targets that disable the package. For these cases, I'm providing the target
 in our package as well.

 We could have of course picked a different target name, but then we would have to add logic to detect if we are NOT an aspnetcore app... By just re-defining the target, we have the same mechanism for removing the generator whether your application references the
 logging.generator package, or the aspnetcore targeting pack, and we are guaranteed to only run once."