Hey @dotnet/aspnet-build, looks like this PR is something you want to take a look at.

@sbomer - any idea what's going on here?

src/Servers/Connections.Abstractions/src/Microsoft.AspNetCore.Connections.Abstractions.csproj(0,0): error NU1603: (NETCORE_ENGINEERING_TELEMETRY=Restore) Warning As Error: Microsoft.AspNetCore.Connections.Abstractions depends on Microsoft.NET.ILLink.Analyzers (>= 8.0.0-preview.6.23304.2) but Microsoft.NET.ILLink.Analyzers 8.0.0-preview.6.23304.2 was not found. An approximate best match of Microsoft.NET.ILLink.Analyzers 8.0.100-1.22608.1 was resolved.

Writing down my answer from our conversation in case anyone else comes across this:

• With Use linker matching TFM sdk#29441, the trim analyzer (imported from the ILLink pack) isn't supported for netstandard2.1. (The behavior was never correct for netstandard2.1, but now we intentionally block the scenario).
• Aspnet has a workaround that defines a KnownILLinkPack for netstandard2.1, using the package version taken from 8.0:

  aspnetcore/eng/tools/GenerateFiles/Directory.Build.targets.in

  Lines 141 to 144 in c2488ee

  	<KnownILLinkPack Include="@(KnownILLinkPack)"
  	Condition="'%(TargetFramework)' == '${DefaultNetCoreTargetFramework}'"
  	TargetFramework="netstandard2.1"
  	ILLinkPackVersion="%(KnownILLinkPack.ILLinkPackVersion)" />

• When targeting net7.0 and below, we add a separate packagereference to the analyzer (since it used to ship as a separate package). With the aspnet workaround this now looks for a non-existent 8.0 package, so restore fails.

I would suggest removing the workaround - then the scenario will fail (depending on the TFM) with an error that indicates the runtime pack is not available. Trimming and trim analysis should be disabled for those TFMs since they are not supported scenarios (see dotnet/linker#3175 for more context).

Adding more notes from investigation with @eerhardt: the specific issue was caused by the aspnet workaround using the 8.0 version for KnownILLinkPack, causing the SDK to look for non-existent Microsoft.NET.ILLink.Analyzers package (since we started shipping analyzers with the ILLink.Tasks package in 8.0). The workaround should be using net7.0 instaed of DefaultNetCoreTargetFramework in the condition, as suggested originally in #45879 (comment).