[mono] Don't build System.Utf8String.Experimental.Tests.csproj tests for mono

[EgorBo]

It fails when we build repo with --subsetCategory mono-libraries

System.Utf8String.Experimental.csproj was already disabled:
https://github.com/dotnet/runtime/blob/master/src/libraries/src.builds#L5

[stephentoub]

Is this the best / only place to do this? We've built the engineering system here such that core files like this one don't need to know about individual test projects, but now we're adding a specific suppression to this general file. There's no way to do this as part of System.Utf8String.Experimental?

[ViktorHofer]

The project shouldn't be loaded at all, hence excluding it in the traversals (tests.proj, src.builds, ref.builds, packages.builds) is fine.

[stephentoub]

I understand, but why can't something be put into the System.Utf8String.Experimental directory that would prevent that as well?

[ViktorHofer]

We currently just glob on csproj files and invoke them in tests.proj and other traversals. We could do an exclusion check based on a file being present in every item's project dir but I doubt that's worth the hassle. Just doing the file globbing in msbuild is already slow. (as an example, we keep a static list of references for the facades in the netstandard package to avoid globbing)

[stephentoub]

Then how bad is it if we just load the project? We're talking about one project out of hundreds that will get loaded and ignored in a test build.

[ViktorHofer]

I'm sure @EgorBo can try that out. To be consistent, the same needs to be done for the ref and the src project which are also excluded.

[akoeplinger]

I'd appreciate if we could merge this and file an issue to make it better to unblock our test build :)

[EgorBo]

I am not a build system expert, how can I disable build for certain libraries in their folders? what property can I use in Directory.Build.props ?

[stephentoub]

I'd appreciate if we could merge this and file an issue to make it better to unblock our test build :)

Ok.

[ViktorHofer]

Filed #34499