Only include DesignTimeFacadeAssemblies which are not in ReferencePath

[cdmihai]

Resolves #1345

[cdmihai]

@dsplaisted @ericstj

I guess you can delete the fix from the SDK now: https://github.com/dotnet/sdk/blob/7eb264f9cc5153b24793878307c4c410bd03ff68/src/Tasks/Microsoft.NET.Build.Tasks/build/Microsoft.NET.Sdk.targets#L285-L320

[cdmihai]

@dotnet-bot test Windows_NT Build for Desktop please

[ericstj]

I was taking another look at this the other day, and while I think this is the smallest tactical fix I noticed something that might be better.

ImplicitlyExpandDesignTimeFacades always adds all facades and causes conflicts, but I noticed that RAR is already getting the path to the facades via $(TargetFrameworkDirectory). I then see that RAR actually selects the subset of facades that are actually needed and outputs them via ReferenceDependencyPaths. What surprised me is that we didn't pass this item to CSC, but other compilers did accept this item. @davkean / @weshaggard do you remember why that is the case?

[weshaggard]

@weshaggard do you remember why that is the case?

No I don't recall why that is the case. I didn't even know RAR was getting the path to the facades at all.

[cdmihai]

If that's the case, then it looks like ImplicitlyExpandDesignTimeFacades would become obsolete if only ReferenceDependencyPaths flowed into the the compiler. Right?

[ericstj]

@cdmihai yeah, I think so. I just don't know why that wasn't done to begin with. Maybe @davkean or someone with more history in this codebase could chime in.

[davkean]

Yeah I don't history on this - I wasn't aware of it.

[cdmihai]

Including some of the committers from the new home of the csc target, maybe they know more.

@tannergooding, @agocke, @AArnott, do you know more about @ericstj's proposal of deleting the ImplicitlyExpandDesignTimeFacades target and changing the CSC task invocation to include the output of RAR, ReferenceDependencyPaths, which supposedly contains the target framework facade dlls? If not, I'll start experimenting with it and see what breaks. The risky part of the change is unknown consequences, since a large population of things flow through RAR and CSC :)

[agocke]

@cdmihai That code is before my time, so unfortunately my advice is just try it and see :)

[cdmihai]

@dotnet-bot test Windows_NT Build for Desktop please

[AndyGerlicher]

@dotnet-bot test Windows_NT Build for Desktop please

[AArnott]

I'm afraid I'm not this deeply familiar with resolving references. @crmann1 may know.