Fix dotnet host resolution under proot (ARM64/Termux)

src/Microsoft.TestPlatform.PlatformAbstractions/common/System/ProcessHelper.cs

@@ -245,6 +245,20 @@ internal static void WaitForErrorStreamToDrain(ManualResetEventSlim? errorStream
     /// <inheritdoc/>
     public string? GetCurrentProcessFileName()
     {
+#if NET
+        // Environment.ProcessPath is more reliable than MainModule under sandboxes such as
+        // proot, which is commonly used to run Linux distributions on Android (e.g. Termux).
+        // proot starts the real executable through an injected loader, and it cannot rewrite
+        // the contents of /proc/self/maps that MainModule is built from. When the loader is
+        // mapped below the executable (as it is on ARM64) MainModule reports the loader
+        // instead of the running dotnet host, which breaks test host resolution.
+        // See https://github.com/microsoft/vstest/issues/16446.
+        if (Environment.ProcessPath is { } processPath)
+        {
+            return processPath;
+        }
+#endif
+
         return _currentProcess.MainModule?.FileName;
     }
 

test/vstest.console.UnitTests/ProcessHelperTests.cs

@@ -1,6 +1,9 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+#if NET
+using System;
+#endif
 using System.Diagnostics;
 using System.Threading;
 
@@ -11,17 +14,44 @@
 namespace Microsoft.VisualStudio.TestPlatform.CommandLine.UnitTests;
 
 /// <summary>
-/// Tests for <see cref="ProcessHelper.WaitForErrorStreamToDrain"/>, the bounded wait that lets the process
+/// Tests for <see cref="ProcessHelper"/>.
+/// </summary>
+/// <remarks>
+/// <see cref="ProcessHelper.WaitForErrorStreamToDrain"/> is the bounded wait that lets the process
 /// exit callback observe the complete standard error output of a crashed test host. Without it, the exit
 /// callback could read the asynchronously-collected stderr before all ErrorDataReceived callbacks had run,
 /// dropping a crash callstack such as "Stack overflow." (the cause of the flaky
 /// RunTestsShouldThrowOnStackOverflowException test).
-/// </summary>
+/// </remarks>
 [TestClass]
 public class ProcessHelperTests
 {
     private const int BudgetMs = 500;
 
+    [TestMethod]
+    public void GetCurrentProcessFileNameShouldReturnThePathOfTheRunningExecutable()
+    {
+        var processHelper = new ProcessHelper();
+
+        string? currentProcessFileName = processHelper.GetCurrentProcessFileName();
+
+        using var currentProcess = Process.GetCurrentProcess();
+        string? mainModuleFileName = currentProcess.MainModule?.FileName;
+
+#if NET
+        // On .NET we prefer Environment.ProcessPath, because MainModule can report an injected loader
+        // rather than the running executable under sandboxes such as proot. See issue #16446.
+        // ProcessPath is nullable, so mirror the fallback the production code performs instead of
+        // assuming it is always set.
+        string? expectedFileName = Environment.ProcessPath ?? mainModuleFileName;
+#else
+        // .NET Framework has no Environment.ProcessPath, so the MainModule behavior must be preserved.
+        string? expectedFileName = mainModuleFileName;
+#endif
+
+        Assert.AreEqual(expectedFileName, currentProcessFileName);
+    }
+
     [TestMethod]
     public void WaitForErrorStreamToDrainShouldReturnOnceTheErrorStreamCloses()
     {