[release/8.0-staging] Add non-public SetEntryAssembly() API to System.Reflection

src/libraries/System.Configuration.ConfigurationManager/tests/System.Configuration.ConfigurationManager.Tests.csproj

@@ -59,7 +59,7 @@
     <Compile Include="System\Configuration\ConfigurationElementTests.cs" />
     <Compile Include="System\Configuration\ConfigurationPropertyAttributeTests.cs" />
     <Compile Include="System\Configuration\ConfigurationPathTests.cs" />
-    <Compile Include="System\Configuration\CustomHostTests.cs" />
+    <Compile Include="System\Configuration\CustomHostTests.cs" Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'" />
     <Compile Include="System\Configuration\ConfigurationPropertyTests.cs" />
     <Compile Include="System\Configuration\ConfigurationTests.cs" />
     <Compile Include="System\Configuration\BasicCustomSectionTests.cs" />

src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/CustomHostTests.cs

@@ -36,8 +36,8 @@ public void FilePathIsPopulatedCorrectly()
         private static void MakeAssemblyGetEntryAssemblyReturnNull()
         {
             typeof(Assembly)
-                .GetField("s_forceNullEntryPoint", BindingFlags.NonPublic | BindingFlags.Static)
-                .SetValue(null, true);
+                .GetMethod("SetEntryAssembly", BindingFlags.Public | BindingFlags.Static)
+                .Invoke(null, new object[]{ null });
 
             Assert.Null(Assembly.GetEntryAssembly());
         }

src/libraries/System.Diagnostics.TraceSource/tests/System.Diagnostics.TraceSource.Tests/DefaultTraceListenerClassTests.cs

@@ -174,8 +174,8 @@ public void EntryAssemblyName_Null_NotIncludedInTrace()
         private static void MakeAssemblyGetEntryAssemblyReturnNull()
         {
             typeof(Assembly)
-                .GetField("s_forceNullEntryPoint", BindingFlags.NonPublic | BindingFlags.Static)
-                .SetValue(null, true);
+                .GetMethod("SetEntryAssembly", BindingFlags.Public | BindingFlags.Static)
+                .Invoke(null, new object[]{ null });
 
             Assert.Null(Assembly.GetEntryAssembly());
         }

src/libraries/System.Private.CoreLib/src/System/Reflection/Assembly.cs

@@ -217,13 +217,39 @@
             return type.Module?.Assembly;
         }
 
+        private static object? s_overriddenEntryAssembly;
+
+        /// <summary>
+        /// Sets the application's entry assembly to the provided assembly object.
+        /// </summary>
+        /// <param name="assembly">
+        /// Assembly object that represents the application's new entry assembly.
+        /// </param>
+        /// <remarks>
+        /// The assembly passed to this function has to be a runtime defined Assembly
+        /// type object. Otherwise, an exception will be thrown.
+        /// </remarks>
+        public static void SetEntryAssembly(Assembly? assembly)
+        {
+            if (assembly is null)
+            {
+                s_overriddenEntryAssembly = string.Empty;
+                return;
+            }
+
+            if (assembly is not RuntimeAssembly)
+                throw new ArgumentException(SR.Argument_MustBeRuntimeAssembly);
+
+            s_overriddenEntryAssembly = assembly;
+        }
+
         // internal test hook
         private static bool s_forceNullEntryPoint;
 
         public static Assembly? GetEntryAssembly()
         {
-            if (s_forceNullEntryPoint)
-                return null;
+            if (s_overriddenEntryAssembly is not null)
+                return s_overriddenEntryAssembly as Assembly;
 
             return GetEntryAssemblyInternal();
         }

src/libraries/System.Reflection/tests/AssemblyTests.cs

@@ -7,10 +7,12 @@
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Reflection.Emit;
 using System.Reflection.Tests;
 using System.Runtime.CompilerServices;
 using System.Security;
 using System.Text;
+using Microsoft.DotNet.RemoteExecutor;
 using Xunit;
 
 [assembly:
@@ -181,6 +183,38 @@ public void GetEntryAssembly()
             Assert.True(correct, $"Unexpected assembly name {assembly}");
         }
 
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public void SetEntryAssembly()
+        {
+            Assert.NotNull(Assembly.GetEntryAssembly());
+
+            RemoteExecutor.Invoke(() =>
+            {
+                SetEntryAssembly(null);
+                Assert.Null(Assembly.GetEntryAssembly());
+
+                Assembly testAssembly = typeof(AssemblyTests).Assembly;
+
+                SetEntryAssembly(testAssembly);
+                Assert.Equal(Assembly.GetEntryAssembly(), testAssembly);
+
+                var invalidAssembly = new PersistedAssemblyBuilder(
+                    new AssemblyName("NotaRuntimeAssemblyTest"),
+                    typeof(object).Assembly
+                );
+                Assert.Throws<ArgumentException>(
+                    () => Assembly.SetEntryAssembly(invalidAssembly)
+                );
+            }).Dispose();
+        }
+
+        private static SetEntryAssembly(Assembly assembly)
+        {
+            typeof(Assembly)
+                .GetMethod("SetEntryAssembly", BindingFlags.Public | BindingFlags.Static)
+                .Invoke(null, new object[]{ assembly });
+        }
+
         [Fact]
         public void GetFile()
         {

src/libraries/System.Reflection/tests/System.Reflection.Tests.csproj

@@ -2,6 +2,7 @@
   <PropertyGroup>
     <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
     <TestRuntime>true</TestRuntime>
+    <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <!-- SYSLIB0013: Uri.EscapeUriString is obsolete
          SYSLIB0037: AssemblyName members HashAlgorithm, ProcessorArchitecture, and VersionCompatibility are obsolete. -->