$(OS) should return only two values - Windows_NT and Unix .

[radical]

Based on the discussion in issue #539, $(OS) property will return
Windows_NT whenever running on windows and Unix for any other OS.

NativeMethodsShared.OSName is used to set that property, hence this is
being changed.

[cdmihai]

@dotnet-bot test this please

[cdmihai]

Should we revert this only for Mono?

[radical]

No, IMO, we should have uniform behavior w.r.t this. Having different behavior will likely cause unnecessary pain. And it doesn't affect compatibility with existing projects.

If the proposed approach in #539 sounds acceptable, then I'll change this PR accordingly. The proposed approach being:

1. $(OS) will have values of Windows_NT and Unix only. On Windows - $(OS)==Windows_NT and only any IsUnixLike platform - $(OS)==Unix.
2. Introduce a new property $(OSName) which would have more specific values like Windows_NT, OSX and Unix. I'm not sure whether Unix is enough here or it should be more specific like Linux, FreeBSD etc.

If the user's requirement is to simply check for "windows or unix-like", then $(OS) can be used. If the requirement is to have more specific behavior, then they can use $(OSName).

@akoeplinger @jonpryor ^

If this is acceptable, then I can update the PR to not revert the patch, hence retain NativeMethodsShared.OSName, set the new property with this and set the $(OS) property explicitly.

[cdmihai]

@joperezr Does this affect corefx in any way? Please also take a look at #539

[joperezr]

@joperezr Does this affect corefx in any way? Please also take a look at #539

In corefx we currently do the 'hack' of setting OSX to Unix because we were seeing issues for this so I don't think that this would cause issues for now, but I'm not sure until I test it.

[AndyGerlicher]

Based on discussion in #539 this should change to only return Windows_NT when Windows, else Unix. You want to update this PR?

[radical]

Sure, I'll do that.

[AndyGerlicher]

LGTM

[cdmihai]

@dotnet-bot test this please