[dotnet][xma] Ensure we don't use DOTNET_ROOT and DOTNET_HOST_PATH in…

msbuild/Messaging/Xamarin.Messaging.Build/TaskRunner.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -10,24 +11,15 @@
 
 namespace Xamarin.Messaging.Build {
 	internal class TaskRunner : ITaskRunner {
-		ITaskSerializer serializer;
-		List<Type> tasks = new List<Type> ();
+		static readonly ITracer tracer = Tracer.Get<TaskRunner> ();
+
+		readonly ITaskSerializer serializer;
+		readonly List<Type> tasks = new List<Type> ();
 
 		internal TaskRunner (ITaskSerializer serializer)
 		{
 			this.serializer = serializer;
-
-			var sdkRootPath = Path.Combine (MessagingContext.GetXmaPath (), "SDKs");
-			var dotnetPath = Path.Combine (sdkRootPath, "dotnet", "dotnet");
-
-			if (File.Exists (dotnetPath)) {
-				Environment.SetEnvironmentVariable ("DOTNET_CUSTOM_HOME", Path.Combine (sdkRootPath, ".home"));
-			} else {
-				//In case the XMA dotnet has not been installed yet
-				dotnetPath = "/usr/local/share/dotnet/dotnet";
-			}
-
-			Environment.SetEnvironmentVariable ("DOTNET_HOST_PATH", dotnetPath);
+			SetDotNetVariables ();
 		}
 
 		internal IEnumerable<Type> Tasks => tasks.AsReadOnly ();
@@ -57,5 +49,68 @@ public ExecuteTaskResult Execute (string taskName, string inputs)
 
 			return result;
 		}
+
+		void SetDotNetVariables ()
+		{
+			var xmaSdkRootPath = Path.Combine (MessagingContext.GetXmaPath (), "SDKs");
+			var xmaDotNetRootPath = Path.Combine (xmaSdkRootPath, "dotnet");
+			var xmaDotNetPath = default (string);
+
+			if (IsValidDotNetInstallation (xmaDotNetRootPath)) {
+				//If the XMA dotnet is already installed, we use it and also declare a custom home for it (for NuGet restore and caches)
+				Environment.SetEnvironmentVariable ("DOTNET_CUSTOM_HOME", Path.Combine (xmaSdkRootPath, ".home"));
+				xmaDotNetPath = GetDotNetPath (xmaDotNetRootPath);
+			} else {
+				//In case the XMA dotnet has not been installed yet, we use the default dotnet installation
+				xmaDotNetPath = GetDefaultDotNetPath ();
+				xmaDotNetRootPath = Path.GetDirectoryName (xmaDotNetPath);
+			}
+
+			var pathContent = GetPathContent ();
+			//We add the XMA dotnet path first so it has priority over the default dotnet installation
+			var newPathContent = $"{xmaDotNetRootPath}:{pathContent}";
+
+			//Override the PATH with the XMA dotnet in it, just in case it's used internally by dotnet
+			Environment.SetEnvironmentVariable ("PATH", newPathContent);
+			//Deprecated dotnet environment variable. We still preserve ir for backwards compatibility with other components that haven't deprecated it yet (like dotnet ILLink)
+			Environment.SetEnvironmentVariable ("DOTNET_HOST_PATH", xmaDotNetPath);
+			//Custom environment variable for internal iOS SDK usage
+			Environment.SetEnvironmentVariable ("DOTNET_CUSTOM_PATH", xmaDotNetPath);
+
+			tracer.Info ($"Using dotnet: {xmaDotNetPath}");
+			tracer.Info ($"Current PATH: {newPathContent}");
+		}
+
+		string GetDefaultDotNetPath ()
+		{
+			var dotnetRootPath = "/usr/local/share/dotnet";
+
+			if (IsValidDotNetInstallation (dotnetRootPath)) {
+				return GetDotNetPath (dotnetRootPath);
+			}
+
+			var dotnetPath = "dotnet";
+			var pathContent = GetPathContent ();
+			var pathElements = pathContent.Split (new string [] { ":" }, StringSplitOptions.RemoveEmptyEntries);
+
+			foreach (var pathElement in pathElements) {
+				try {
+					if (IsValidDotNetInstallation (pathElement)) {
+						dotnetPath = GetDotNetPath (pathElement);
+						break;
+					}
+				} catch {
+					//If we can't read a directory for any reason just skip it
+				}
+			}
+
+			return dotnetPath;
+		}
+
+		string GetPathContent () => Environment.GetEnvironmentVariable ("PATH") ?? "";
+
+		bool IsValidDotNetInstallation (string rootPath) => File.Exists (GetDotNetPath (rootPath));
+
+		string GetDotNetPath (string rootPath) => Path.Combine (rootPath, "dotnet");
 	}
 }

msbuild/Xamarin.MacDev.Tasks/Extensions/TaskExtensions.cs

@@ -5,5 +5,22 @@ namespace Microsoft.Build.Tasks {
 	public static class TaskExtensions {
 		public static bool ShouldExecuteRemotely (this Task task, string sessionId)
 			=> Environment.OSVersion.Platform == PlatformID.Win32NT && !string.IsNullOrEmpty (sessionId);
+
+		public static string GetDotNetPath (this Task task)
+		{
+			//Custom environment variable set by the XMA Build Agent
+			var dotnetPath = Environment.GetEnvironmentVariable ("DOTNET_CUSTOM_PATH");
+
+			if (string.IsNullOrEmpty (dotnetPath)) {
+				//Deprecated dotnet environment variable used for backwards compatibility
+				dotnetPath = Environment.GetEnvironmentVariable ("DOTNET_HOST_PATH");
+			}
+
+			if (string.IsNullOrEmpty (dotnetPath)) {
+				dotnetPath = Environment.OSVersion.Platform == PlatformID.Win32NT ? "dotnet.exe" : "dotnet";
+			}
+
+			return dotnetPath;
+		}
 	}
 }

msbuild/Xamarin.MacDev.Tasks/Tasks/BTouchTaskBase.cs

@@ -8,6 +8,7 @@
 
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
+using Microsoft.Build.Tasks;
 
 using Xamarin.Utils;
 using Xamarin.Localization.MSBuild;
@@ -75,26 +76,10 @@ public abstract class BTouchTaskBase : XamarinToolTask {
 		[Required]
 		public string ResponseFilePath { get; set; }
 
-		string DotNetPath {
-			get {
-				// Return the dotnet executable we're executing with.
-				var dotnet_path = Environment.GetEnvironmentVariable ("DOTNET_HOST_PATH");
-				if (!string.IsNullOrEmpty (dotnet_path))
-					return dotnet_path;
-
-				if (Environment.OSVersion.Platform == PlatformID.Win32NT) {
-					// This might happen when building from inside VS (design-time builds, etc.)
-					return "dotnet.exe";
-				}
-
-				throw new InvalidOperationException ($"DOTNET_HOST_PATH is not set");
-			}
-		}
-
 		protected override string ToolName {
 			get {
 				if (IsDotNet)
-					return Path.GetFileName (DotNetPath);
+					return Path.GetFileName (this.GetDotNetPath ());
 
 				return Path.GetFileNameWithoutExtension (ToolExe);
 			}
@@ -108,7 +93,7 @@ protected override string GenerateFullPathToTool ()
 			// system dotnet, which might not exist or not have the version we
 			// need.
 			if (IsDotNet)
-				return DotNetPath;
+				return this.GetDotNetPath ();
 
 			return Path.Combine (ToolPath, ToolExe);
 		}

msbuild/Xamarin.MacDev.Tasks/Tasks/ComputeRemoteGeneratorPropertiesTaskBase.cs

@@ -4,6 +4,7 @@
 using System.IO;
 
 using Microsoft.Build.Framework;
+using Microsoft.Build.Tasks;
 
 using Xamarin.Localization.MSBuild;
 using Xamarin.Utils;
@@ -93,9 +94,8 @@ void ComputeProperties ()
 			var environment = default (Dictionary<string, string?>);
 
 			if (IsDotNet) {
-				executable = Environment.GetEnvironmentVariable ("DOTNET_HOST_PATH");
-				if (string.IsNullOrEmpty (executable))
-					executable = "dotnet";
+				executable = this.GetDotNetPath ();
+
 				arguments.Add ("build");
 
 				var customHome = Environment.GetEnvironmentVariable ("DOTNET_CUSTOM_HOME");

msbuild/Xamarin.MacDev.Tasks/Tasks/XamarinBuildTask.cs

@@ -3,6 +3,7 @@
 using System.IO;
 using System.Linq;
 using Microsoft.Build.Framework;
+using Microsoft.Build.Tasks;
 using Xamarin.Localization.MSBuild;
 using Threading = System.Threading.Tasks;
 
@@ -35,12 +36,7 @@ protected string ComputeValueUsingTarget (string computeValueTarget, string targ
 ";
 			File.WriteAllText (projectPath, csproj);
 
-			var dotnetPath = Environment.GetEnvironmentVariable ("DOTNET_HOST_PATH");
-
-			if (string.IsNullOrEmpty (dotnetPath)) {
-				dotnetPath = "dotnet";
-			}
-
+			var dotnetPath = this.GetDotNetPath ();
 			var environment = default (Dictionary<string, string>);
 			var customHome = Environment.GetEnvironmentVariable ("DOTNET_CUSTOM_HOME");