Return host's file path when using Environment.GetCommandLineArgs()[0] in single-file apps

src/coreclr/src/vm/corhost.cpp

@@ -272,7 +272,7 @@ void SetCommandLineArgs(LPCWSTR pwzAssemblyPath, int argc, LPCWSTR* argv)
     GCPROTECT_BEGIN(gc);
 
     gc.cmdLineArgs = (PTRARRAYREF)AllocateObjectArray(argc + 1 /* arg[0] should be the exe name*/, g_pStringClass);
-    OBJECTREF orAssemblyPath = StringObject::NewString(pwzAssemblyPath);
+    OBJECTREF orAssemblyPath = StringObject::NewString(Bundle::AppIsBundle() ? static_cast<LPCWSTR>(Bundle::AppBundle->Path()) : pwzAssemblyPath);
     gc.cmdLineArgs->SetAt(0, orAssemblyPath);
 
     for (int i = 0; i < argc; ++i)

src/installer/tests/Assets/TestProjects/EnvironmentGetCommandLineArgs/EnvironmentGetCommandLineArgs.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
+    <OutputType>Exe</OutputType>
+    <RuntimeIdentifier>$(TestTargetRid)</RuntimeIdentifier>
+    <RuntimeFrameworkVersion>$(MNAVersion)</RuntimeFrameworkVersion>
+  </PropertyGroup>
+
+</Project>

src/installer/tests/Assets/TestProjects/EnvironmentGetCommandLineArgs/Program.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace EnvironmentGetCommandLineArgs
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            foreach (var arg in Environment.GetCommandLineArgs())
+            {
+                Console.WriteLine(arg);
+            }
+        }
+    }
+}

src/installer/tests/Microsoft.NET.HostModel.Tests/AppHost.Bundle.Tests/BundleEnvironmentGetCommandLineArgs.cs

@@ -0,0 +1,75 @@
+using System;
+using BundleTests.Helpers;
+using Microsoft.DotNet.Cli.Build.Framework;
+using Microsoft.DotNet.CoreSetup.Test;
+using Xunit;
+
+namespace AppHost.Bundle.Tests
+{
+    public class BundleEnvironmentGetCommandLineArgs : IClassFixture<BundleEnvironmentGetCommandLineArgs.SharedTestState>
+    {
+        private SharedTestState sharedTestState;
+
+        public BundleEnvironmentGetCommandLineArgs(SharedTestState fixture)
+        {
+            sharedTestState = fixture;
+        }
+
+        [Fact]
+        public void GetEnvironmentArgs_0_Returns_Bundled_Executable_Path()
+        {
+            var fixture = sharedTestState.TestFixture.Copy();
+            var singleFile = BundleHelper.BundleApp(fixture);
+
+            // For single-file, Environment.GetCommandLineArgs[0]
+            // should return the file path of the host.
+            Command.Create(singleFile)
+                .CaptureStdErr()
+                .CaptureStdOut()
+                .Execute()
+                .Should()
+                .Pass()
+                .And
+                .HaveStdOutContaining(singleFile);
+        }
+
+        [Fact]
+        public void GetEnvironmentArgs_0_Non_Bundled_App()
+        {
+            var fixture = sharedTestState.TestFixture.Copy();
+            var dotnet = fixture.BuiltDotnet;
+            var appPath = BundleHelper.GetAppPath(fixture);
+
+            // For non single-file apps, Environment.GetCommandLineArgs[0]
+            // should return the file path of the managed entrypoint.
+            dotnet.Exec(appPath)
+                .CaptureStdErr()
+                .CaptureStdOut()
+                .Execute()
+                .Should()
+                .Pass()
+                .And
+                .HaveStdOutContaining(appPath);
+        }
+
+        public class SharedTestState : IDisposable
+        {
+            public TestProjectFixture TestFixture { get; set; }
+            public RepoDirectoriesProvider RepoDirectories { get; set; }
+
+            public SharedTestState()
+            {
+                RepoDirectories = new RepoDirectoriesProvider();
+                TestFixture = new TestProjectFixture("EnvironmentGetCommandLineArgs", RepoDirectories);
+                TestFixture
+                    .EnsureRestoredForRid(TestFixture.CurrentRid, RepoDirectories.CorehostPackages)
+                    .PublishProject(runtime: TestFixture.CurrentRid, outputDirectory: BundleHelper.GetPublishPath(TestFixture));
+            }
+
+            public void Dispose()
+            {
+                TestFixture.Dispose();
+            }
+        }
+    }
+}