FindPythonTask.targets

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    
    <!-- From: https://learn.microsoft.com/en-us/visualstudio/msbuild/msbuild-roslyncodetaskfactory -->
    <UsingTask TaskName="FindPythonTask" TaskFactory="RoslynCodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll">
        <Task>
            <Code Type="Class" Language="cs">
                <![CDATA[
#nullable enable
using System;
using System.Diagnostics;
using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;
using Task = Microsoft.Build.Utilities.Task;

public class FindPythonTask : Task
{
    [Output]
    public string PythonPath { get; set; } = "";

    private static string? CachedPythonPath;
    
    public override bool Execute()
    {
        if (CachedPythonPath != null) {
            PythonPath = CachedPythonPath;
            return true;
        }

        string[] pythons = { 
            "python3",
            "python"
        };

        foreach (string python in pythons) {
            if (IsPythonValid(python)) {
                PythonPath = python;
                CachedPythonPath = python;
                return true;
            }
        }
        
        Log.LogError($"Couldn't not find python on the PATH. Tried: {pythons}");
        return false;
    }
    
    private bool IsPythonValid(string python)
    {
        bool isPythonValid = false;
        
        Process process = new Process();
        process.StartInfo = new ProcessStartInfo {
            FileName = python,
            CreateNoWindow = true,
            Arguments = "--version",
            RedirectStandardOutput = true
        };
        try {
            process.Start();
            try {
                process.WaitForExit(1000 * 10);
                string outputLine = process.StandardOutput.ReadLine() ?? "";
                isPythonValid = outputLine.ToLowerInvariant().StartsWith("python 3");
            } finally {
                process.Kill();
            }
        } catch { }
        return isPythonValid;
    }        
}
]]>
            </Code>
        </Task>
    </UsingTask>
</Project>