Fix downlevel build break in TensorPrimitives

[stephentoub]

No description provided.

[stephentoub]

/backport to release/8.0

[ghost]

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Issue Details

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Author:	stephentoub
Assignees:	-
Labels:	area-System.Numerics
Milestone:	-

[github-actions]

Started backporting to release/8.0: https://github.com/dotnet/runtime/actions/runs/6235610540

[ericstj]

This needs more based on the changes I have in 8.0. Should we bring those here too? Maybe it makes sense to include net6.0 in main so you have coverage of the frameworks building in 8.0.

[ericstj]

Hmm, this seems to have added prebuilts.

error : 2 new pre-builts discovered! Detailed usage report can be found at /__w/1/s/artifacts/source-build/self/prebuilt-report/baseline-comparison.xml. See https://aka.ms/dotnet/prebuilts for guidance on what pre-builts are and how to eliminate them. Package IDs are: Microsoft.NETCore.App.Ref.6.0.20 Microsoft.NETCore.App.Ref.7.0.9

Maybe we should avoid building against 6.0 and 7.0 when building in sourcebuild? @mthalman what do you reccomend?

[ericstj]

I see, here's what we do for the other frameworks;

runtime/Directory.Build.props

Lines 93 to 98 in d3da653

	<NetCoreAppPrevious Condition="'$(DotNetBuildFromSource)' == 'true'">$(NetCoreAppCurrent)</NetCoreAppPrevious>
	<!-- The minimum supported .NET version. -->
	<NetCoreAppMinimum>net6.0</NetCoreAppMinimum>
	<NetCoreAppMinimum Condition="'$(DotNetBuildFromSource)' == 'true'">$(NetCoreAppCurrent)</NetCoreAppMinimum>

I'll condition out the 6.0 and 7.0 so they aren't there for source build.

[stephentoub]

Thanks for the additional tweaks, @ericstj.

[ViktorHofer]

I just saw this PR. I don't see an underlying issue that is fixed by this change, what was the motivation to add net7.0 and net6.0 TFMs to this library?

.NET 9 dotnet/runtime libraries packages support net8.0 (NetMinimum) and net9.0 (NetCurrent) only.

Looking at the latest package from main, I see that a warning is emitted at consumption time when targeting net6.0 or net7.0: https://dnceng.visualstudio.com/public/_artifacts/feed/dotnet9/NuGet/System.Numerics.Tensors/overview/9.0.0-alpha.1.23519.15

System.Numerics.Tensors 9.0.0-alpha.1.23519.15 doesn't support net7.0 and has not been tested with it. Consider upgrading your TargetFramework to net8.0 or later. You may also set <SuppressTfmSupportBuildWarnings>true</SuppressTfmSupportBuildWarnings> in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk.