Environment.OSVersion.Platform returns Unix on macOS

[yaakov-h]

Using .NET Core 2.0 SDK preview.

dotnet --info:

.NET Command Line Tools (2.0.0-preview1-005977)

Product Information:
 Version:            2.0.0-preview1-005977
 Commit SHA-1 hash:  414cab8a0b

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.12
 OS Platform: Darwin
 RID:         osx.10.12-x64
 Base Path:   /usr/local/share/dotnet/sdk/2.0.0-preview1-005977/

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.0-preview1-002111-00
  Build    : 1ff021936263d492539399688f46fd3827169983

Simple test case:

[12:41pm yaakov@Eadu:/tmp/osver] dotnet new console
The template "Console Application" was created successfully.

Processing post-creation actions...
Running 'dotnet restore' on /private/tmp/osver/osver.csproj...
Restore succeeded.

[12:41pm yaakov@Eadu:/tmp/osver] vim Program.cs 
[12:42pm yaakov@Eadu:/tmp/osver] cat Program.cs 
using System;

namespace osver
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(Environment.OSVersion.Platform);
        }
    }
}
[12:42pm yaakov@Eadu:/tmp/osver] dotnet restore && dotnet build && dotnet run
  Restoring packages for /private/tmp/osver/osver.csproj...
  Lock file has not changed. Skipping lock file write. Path: /private/tmp/osver/obj/project.assets.json
  Restore completed in 177.16 ms for /private/tmp/osver/osver.csproj.
  
  NuGet Config files used:
      /Users/yaakov/.nuget/NuGet/NuGet.Config
  
  Feeds used:
      https://api.nuget.org/v3/index.json
      /Users/yaakov/.dotnet/NuGetFallbackFolder
Microsoft (R) Build Engine version 15.3.117.23532
Copyright (C) Microsoft Corporation. All rights reserved.

  osver -> /private/tmp/osver/bin/Debug/netcoreapp2.0/osver.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:02.29
Unix
[12:42pm yaakov@Eadu:/tmp/osver] 

I would expect the program to print MacOSX, i.e. System.PlatformID.MacOSX which is enum value 6.

[danmoseley]

@stephentoub it is hard coded that way - there is no Environment.OSX.cs. Is there any reason for that?

[yaakov-h]

Environment.Unix.cs has a whole lot of IsMac conditionals - I'd suggest either add one more (:smile:), or split it out into an Environment.OSX.cs.

[ViktorHofer]

There isn't a lot difference between the Unix and MacOSX implementation. I think the few times the IsMac property is used doesn't suffice an extra file.

[justinvp]

@stephentoub it is hard coded that way - there is no Environment.OSX.cs. Is there any reason for that?

It's hard coded that way to match Mono's behavior of returning Unix on macOS.

[ViktorHofer]

@justinvp Thanks for that! I didn't know that this behavior is intentional. Will wait what @stephentoub has to say about.

[yaakov-h]

Without jumping the gun of waiting for Stephen, if that is indeed the case then what is the purpose of PlatformID.MacOSX if no .NET runtime ever returns that value?

[justinvp]

what is the purpose of PlatformID.MacOSX if no .NET runtime ever returns that value?

PlatformID.MacOSX was added for Silverlight to return on OSX. I wish we hadn't added that and instead returned PlatformID.Unix on OSX like Mono.

See also:
https://github.com/dotnet/corefx/issues/11878
https://github.com/terrajobst/platform-compat/issues/29

[yaakov-h]

So to figure out the current OS X version you need to combine RuntimeInformation.IsOSPlatform(OSPlatform.OSX) with Environment.OSVersion.Version and ignore Environment.OSVersion.Platform? That sounds like an accident waiting to happen...

[stephentoub]

Will wait what @stephentoub has to say about.

What Justin said.

[stephentoub]

We can of course re-evaluate the design. If we want to make a change here, we should do it for 2.0 or live with it. It's a hard call; on the one hand, MacOSX is obviously the "tighter" answer (Unix is still correct), but on the other hand, we only brought OSVersion back to help with bringing over existing code, and existing code on desktop would only ever care about Windows vs non-Windows, and existing code from Mono would be expecting Unix on macOS, so I still think aligning with Unix is the slightly better path.

[svick]

@stephentoub

we only brought OSVersion back to help with bringing over existing code

But how am going to learn that if I'm writing new code? I think it would be nice if https://github.com/dotnet/corefx/issues/11878 was addressed for 2.0. Whether the decision is to use [Obsolete] or IntelliSense hiding or something else does not matter much, but something should be done.

[stephentoub]

but something should be done.

And aligned with Mono how?
cc: @akoeplinger, @marek-safar

[akoeplinger]

We won't be changing what Mono returns as it'd break too much code. MSBuild is also returning Unix for $(OS) even on macOS. Yes this is pretty unfortunate but I don't see it changing...

I think applying [EditorBrowsable(false)] to the MacOSX enum value to hide it from IntelliSense does make sense.

[marek-safar]

I think it's good this enum is available for backward compatibility but when the type was re-introduced it should be marked immediately obsolete and replaced with something what is not broken by design. I has been quite painful during past 15 years to explain over and over again that this type exists but to use it you need to understand whole history of .NET.

http://www.mono-project.com/docs/faq/technical/#how-to-detect-the-execution-platform

[danmoseley]

@svick terrajobst/platform-compat#29 tool may help detect this.