Fix dotnet path for RoslynCodeTaskFactory

Author: GangWang01

src/Tasks.UnitTests/RoslynCodeTaskFactory_Tests.cs

@@ -1068,6 +1068,61 @@ public override bool Execute()
             }
         }
 
+        [Fact]
+        public void RoslynCodeTaskFactory_UsingAPI()
+        {
+            string text = $@"
+<Project>
+
+  <UsingTask
+    TaskName=""Custom1""
+    TaskFactory=""RoslynCodeTaskFactory""
+    AssemblyFile=""$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll"" >
+    <ParameterGroup>
+      <SayHi ParameterType=""System.String"" Required=""true"" />
+    </ParameterGroup>
+    <Task>
+      <Reference Include=""{typeof(Enumerable).Assembly.Location}"" />
+      <Code Type=""Fragment"" Language=""cs"">
+        <![CDATA[
+        string sayHi = ""Hello "" + SayHi;
+        Log.LogMessage(sayHi);
+        ]]>
+      </Code>
+    </Task>
+  </UsingTask>
+
+    <Target Name=""Build"">
+        <Custom1 SayHi=""World"" />
+    </Target>
+
+</Project>";
+
+            using var env = TestEnvironment.Create();
+#if !FEATURE_RUN_EXE_IN_TESTS
+            RunnerUtilities.ApplyDotnetHostPathEnvironmentVariable(env);
+#endif
+
+            var project = env.CreateTestProjectWithFiles("p1.proj", text);
+
+            var logger = project.BuildProjectExpectSuccess();
+#if !FEATURE_RUN_EXE_IN_TESTS
+            var filter = "dotnet path is ";
+#else
+            var filter = "Compiling task source code";
+
+#endif
+            var logLines = logger.AllBuildEvents.Select(a => a.Message);
+            var log = string.Join("\n", logLines);
+            var messages = logLines.Where(l => l.Contains(filter)).ToList();
+            messages.Count.ShouldBe(1, log);
+#if !FEATURE_RUN_EXE_IN_TESTS
+            var dotnetPath = messages[0].Replace(filter, string.Empty);
+            bool isFilePath = File.Exists(dotnetPath);
+            isFilePath.ShouldBeTrue(dotnetPath);
+#endif
+        }
+
         private void TryLoadTaskBodyAndExpectFailure(string taskBody, string expectedErrorMessage)
         {
             if (expectedErrorMessage == null)

src/Tasks/RoslynCodeTaskFactory/RoslynCodeTaskFactoryCompilers.cs

@@ -4,6 +4,7 @@
 using System;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
 
@@ -14,7 +15,7 @@ namespace Microsoft.Build.Tasks
     internal abstract class RoslynCodeTaskFactoryCompilerBase : ToolTaskExtension
     {
 #if RUNTIME_TYPE_NETCORE
-        private static readonly string DotnetCliPath = System.Diagnostics.Process.GetCurrentProcess().MainModule.FileName;
+        private readonly string dotnetCliPath;
 #endif
 
         private readonly Lazy<string> _executablePath;
@@ -43,6 +44,26 @@ protected RoslynCodeTaskFactoryCompilerBase()
             }, isThreadSafe: true);
 
             StandardOutputImportance = MessageImportance.Low.ToString("G");
+
+#if RUNTIME_TYPE_NETCORE
+            // Tools and MSBuild Tasks within the SDK that invoke binaries via the dotnet host are expected
+            // to honor the environment variable DOTNET_HOST_PATH to ensure a consistent experience.
+            dotnetCliPath = Environment.GetEnvironmentVariable("DOTNET_HOST_PATH");
+            if (string.IsNullOrEmpty(dotnetCliPath))
+            {
+                // Fallback to get dotnet path from current process which might be dotnet executable.
+                dotnetCliPath = System.Diagnostics.Process.GetCurrentProcess().MainModule.FileName;
+            }
+
+            // If dotnet path is not found, rely on dotnet via the system's PATH
+            bool runningOnWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
+            string exeSuffix = runningOnWindows ? ".exe" : string.Empty;
+            var dotnetFileName = $"dotnet{exeSuffix}";
+            if (!dotnetCliPath.EndsWith(dotnetFileName, StringComparison.OrdinalIgnoreCase))
+            {
+                dotnetCliPath = "dotnet";
+            }
+#endif
         }
 
         public bool? Deterministic { get; set; }
@@ -99,7 +120,8 @@ protected override string GenerateFullPathToTool()
             }
 
 #if RUNTIME_TYPE_NETCORE
-            return DotnetCliPath;
+            Log.LogMessageFromText($"dotnet path is {dotnetCliPath}", StandardOutputImportanceToUse);
+            return dotnetCliPath;
 #else
             return _executablePath.Value;
 #endif

src/UnitTests.Shared/RunnerUtilities.cs

@@ -15,6 +15,12 @@ public static class RunnerUtilities
         public static string PathToCurrentlyRunningMsBuildExe => BuildEnvironmentHelper.Instance.CurrentMSBuildExePath;
 #if !FEATURE_RUN_EXE_IN_TESTS
         private static readonly string s_dotnetExePath = EnvironmentProvider.GetDotnetExePath();
+
+        public static void ApplyDotnetHostPathEnvironmentVariable(TestEnvironment testEnvironment)
+        {
+            // Built msbuild.dll executed by dotnet.exe needs this environment variable for msbuild tasks such as RoslynCodeTaskFactory.
+            testEnvironment.SetEnvironmentVariable("DOTNET_HOST_PATH", s_dotnetExePath);
+        }
 #endif
 
         /// <summary>