NETSDK1138 not generated for .NET 6

[Falco20019]

Describe the bug

NETSDK1138 is currently not generated for .NET 6 when using the .NET 9 SDK. It went EOL when .NET 9 was released. https://learn.microsoft.com/de-de/dotnet/core/tools/sdk-errors/netsdk1138 is showing that .NET 6 is considered EOL, so I would have expected to receive this warning.

https://github.com/dotnet/sdk/blob/main/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.EolTargetFrameworks.targets#L27

sdk/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.EolTargetFrameworks.targets

Lines 23 to 28 in 9142933

	<ItemGroup>
	<_EolNetCoreTargetFrameworkVersions Include="1.0;1.1;2.0;2.1;2.2;3.0;3.1;5.0;7.0" />
	</ItemGroup>
	<PropertyGroup>
	<_MinimumNonEolSupportedNetCoreTargetFramework>net6.0</_MinimumNonEolSupportedNetCoreTargetFramework>
	</PropertyGroup>

is currently still not checking for .NET 6 as well as

sdk/test/Microsoft.NET.Build.Tests/GivenThatWeWantToTargetEolFrameworks.cs

Lines 12 to 19 in 9142933

	[Theory]
	[InlineData("netcoreapp1.0")]
	[InlineData("netcoreapp2.1")]
	[InlineData("netcoreapp3.0")]
	[InlineData("netcoreapp3.1")]
	[InlineData("net5.0")]
	[InlineData("net7.0")]
	public void It_warns_that_framework_is_out_of_support(string targetFrameworks)

Please check if this is intentional. It was also not changed for .NET 10 Preview 1 so far.

To Reproduce

• Create a new console application
• Change target framework to net6.0
• Compile

Exceptions (if any)

None, would have expected to see NETSDK1138 nowadays. It's currently only blocked explicitly for net6.0-android through https://github.com/dotnet/android/blob/main/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/Sdk/Eol.targets

Or is this expected to happen at a later point in time? I see in the history that .NET 7 was added in September 2024 when it went EOL in May 2024.

[marcpopMSFT]

I don't know if we have it documented anywhere but we add the build warning 6 months after a runtime goes out of support. We add a warning in VS right away but delay the build warning based on prior feedback.

[copilot-swe-agent]

@marcpopMSFT Unfortunately I hit an unexpected error while trying to work on issue #46640. I've automatically reported this to GitHub.

You can ask me to try again later by unassigning and then reassigning the issue to me again.

If you want to contact GitHub about this error, please mention the following identifier so they can better serve you: e61868a1-9643-4475-b41b-e6651fdf136f

Sorry for the inconvenience!