macOS: get_coreclr fails if run in an already open Terminal window after a fresh dotnet install. Works on Windows.

[DareDevilDenis]

On macOS with pythonnet 3.0.0a2 installed (clr-loader 0.1.7) but without .NET core installed:

• Open a terminal window
• Download and install the correct .NET runtime (by double clicking the installer in Finder)
• In the same terminal window, run a Python script that has:
  get_coreclr(C:\MyApp.runtimeconfig.json)

This results in the following exception:

  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/MyPackage/my_script.py", line 28, in <module>
    runtime_config_path = get_coreclr(r'C:\MyApp.runtimeconfig.json')
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/clr_loader/__init__.py", line 42, in get_coreclr
    dotnet_root = find_dotnet_root()
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/clr_loader/util/find.py", line 22, in find_dotnet_root
    raise RuntimeError("Can not determine dotnet root")
RuntimeError: Can not determine dotnet root

If a NEW Terminal window is opened then this error does not occur. However we should not have to open a new Terminal window for it to find the dotnet executable. Performing the same steps on Windows works fine - we don't need to open a new command window.

My application has the prerequisites that pythonnet and .NET runtime are first installed. I am getting reports from people that they have installed the prerequisites but it is still failing. They don't realise that they need to open a new Terminal window to get it working.

The reason for the exception seems to be in clr-loader/util/find.py there is a difference how it finds the "dotnet" executable between Windows and macOS:

• Windows just looks in C:\Program Files\dotnet
• On macOS however, the line dotnet_path = shutil.which("dotnet") doesn't find anything because dotnet is not in the path for this Terminal window.

def find_dotnet_root() -> str:
    dotnet_root = os.environ.get("DOTNET_ROOT", None)
    if dotnet_root is not None:
        return dotnet_root

    if sys.platform == "win32":
        # On Windows, the host library is stored separately from dotnet.exe for x86
        prog_files = os.environ.get("ProgramFiles")
        dotnet_root = os.path.join(prog_files, "dotnet")
        if os.path.isdir(dotnet_root):
            return dotnet_root

    # Try to discover dotnet from PATH otherwise
    dotnet_path = shutil.which("dotnet")
    if not dotnet_path:
        raise RuntimeError("Can not determine dotnet root")

To fix this, could macOS just look in /usr/local/share/dotnet ?
(I'm don't have Linux so I'm not sure where dotnet gets installed to on Linux)

[filmor]

I'd be fine with special-casing this for macOS.

PRs are welcome, I have no mac to test this. The CI doesn't have this problem as it (properly, IMO) sets PATH and DOTNET_ROOT.

[filmor]

And by the way, the reason this is special-cased on Windows is that on this system one expects it to always install into Program Files and to not update the global PATH. On Unix systems, I expect things to be in PATH after installation. The error here happens because the profile (i.e. set of environment variables) is not automagically updated, you'd need to add that to your installation routine.

[DareDevilDenis]

Thanks @filmor

Based on your advice, we could add the following which would make it work on macOS:

def find_dotnet_root() -> str:
    dotnet_root = os.environ.get("DOTNET_ROOT", None)
    if dotnet_root is not None:
        return dotnet_root

    if sys.platform == "win32":
        # On Windows, the host library is stored separately from dotnet.exe for x86
        prog_files = os.environ.get("ProgramFiles")
        dotnet_root = os.path.join(prog_files, "dotnet")
        ## if os.path.isdir(dotnet_root):            MOVED BELOW
        ##    return dotnet_root                     MOVED BELOW

    ### START NEW 

    if sys.platform == "darwin":
        dotnet_root = r'/usr/local/share/dotnet'

    if os.path.isdir(dotnet_root):
        return dotnet_root
        
    ### END NEW
    

    # Try to discover dotnet from PATH otherwise
    dotnet_path = shutil.which("dotnet")
    if not dotnet_path:
        raise RuntimeError("Can not determine dotnet root")
        

I have a few questions:

• Do you know if there is any way for the user to install .NET Core to a non-default location?
  This page: https://docs.microsoft.com/en-us/dotnet/core/tools/dotnet-environment-variables#:~:text=DOTNET_ROOT%20%2C%20DOTNET_ROOT(x86)&text=The%20default%20location%20on%20Linux,on%20a%2064%2Dbit%20OS. says:

  • DOTNET_ROOT, DOTNET_ROOT(x86)
    Specifies the location of the .NET runtimes, if they are not installed in the default location. The default location on Windows is C:\Program Files\dotnet. The default location on Linux and macOS is /usr/share/dotnet.

  However, for the Windows and macOS installers I couldn't see a way to change the install location.
  On my macOS, .NET was installed to: /usr/local/share/dotnet which agrees with https://stackoverflow.com/questions/38567353/how-to-determine-if-net-core-is-installed which says:

  • "On macOS you could check .net core version by using below command.
    ls /usr/local/share/dotnet/shared/Microsoft.NETCore.App/"

  Strangely, the Microsoft link above says:

  • DOTNET_ROOT, DOTNET_ROOT(x86)
    Specifies the location of the .NET runtimes, if they are not installed in the default location. The default location on Windows is C:\Program Files\dotnet. The default location on Linux and macOS is /usr/share/dotnet.

  Why does it say that the default location on macOS is /usr/share/dotnet when it's actually /usr/local/share/dotnet ?

• On my Windows and macOS installations, there is no "DOTNET_ROOT" environment variable. How does this get set?

• I'm not interested in Linux (I don't have a Linux machine), but I see that the following pages say that .NET is installed to /usr/share/dotnet/ (which agrees with the microsoft link)
  https://stackoverflow.com/questions/45523961/where-is-the-dotnet-runtime-installed-to-on-ubuntu
  https://stackoverflow.com/questions/38567353/how-to-determine-if-net-core-is-installed

  Should we add the following clause?

    if sys.platform == "linux":
        dotnet_root = r'/usr/share/dotnet'

[filmor]

DOTNET_ROOT is something that you can set yourself. That change seems fine to me, please create a PR. I don't want to set a default on Linux, on all reasonable Linux systems, you will have dotnet on the PATH. Your other questions should be directed at Microsoft :)

[DareDevilDenis]

Thanks @filmor. I've created the PR: #25

[filmor]

Thank you :)