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.

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.