[illink] set $(StartupHookSupport)=false *only* for Release mode

src/Mono.Android/Android.Runtime/JNIEnvInit.cs

@@ -165,13 +165,50 @@ internal static unsafe void Initialize (JnienvInitializeArgs* args)
 			}
 
 			args->propagateUncaughtExceptionFn = (IntPtr)(delegate* unmanaged<IntPtr, IntPtr, IntPtr, void>)&PropagateUncaughtException;
-
+			RunStartupHooksIfNeeded ();
 			SetSynchronizationContext ();
 		}
 
 		[DllImport (RuntimeConstants.InternalDllName, CallingConvention = CallingConvention.Cdecl)]
 		static extern unsafe void xamarin_app_init (IntPtr env, delegate* unmanaged <int, int, int, IntPtr*, void> get_function_pointer);
 
+		static void RunStartupHooksIfNeeded ()
+		{
+			// Return if startup hooks are disabled or not CoreCLR
+			if (!RuntimeFeature.IsCoreClrRuntime)
+				return;
+			if (!RuntimeFeature.StartupHookSupport)
+				return;
+
+			RunStartupHooks ();
+		}
+
+		[RequiresUnreferencedCode ("Uses reflection to access System.StartupHookProvider.")]
+		static void RunStartupHooks ()
+		{
+			const string typeName = "System.StartupHookProvider";
+			const string methodName = "ProcessStartupHooks";
+
+			var type = typeof(object).Assembly.GetType (typeName, throwOnError: false);
+			if (type is null) {
+				RuntimeNativeMethods.monodroid_log (LogLevel.Warn, LogCategories.Default,
+					$"Could not load type '{typeName}'. Skipping startup hooks.");
+				return;
+			}
+
+			var method = type.GetMethod (methodName, 
+				BindingFlags.NonPublic | BindingFlags.Static, null, [ typeof(string) ], null);
+			if (method is null) {
+				RuntimeNativeMethods.monodroid_log (LogLevel.Warn, LogCategories.Default,
+					$"Could not load method '{typeName}.{methodName}'. Skipping startup hooks.");
+				return;
+			}
+
+			// Pass empty string for diagnosticStartupHooks parameter
+			// The method will read STARTUP_HOOKS from AppContext internally
+			method.Invoke (null, [ "" ]);
+		}
+
 		static void SetSynchronizationContext () =>
 			SynchronizationContext.SetSynchronizationContext (Android.App.Application.SynchronizationContext);
 	}

src/Mono.Android/Microsoft.Android.Runtime/RuntimeFeature.cs

@@ -9,8 +9,10 @@ static class RuntimeFeature
 	const bool IsMonoRuntimeEnabledByDefault = true;
 	const bool IsCoreClrRuntimeEnabledByDefault = false;
 	const bool IsAssignableFromCheckEnabledByDefault = true;
+	const bool StartupHookSupportEnabledByDefault = true;
 
 	const string FeatureSwitchPrefix = "Microsoft.Android.Runtime.RuntimeFeature.";
+	const string StartupHookProviderSwitch = "System.StartupHookProvider.IsSupported";
 
 	[FeatureSwitchDefinition ($"{FeatureSwitchPrefix}{nameof (ManagedTypeMap)}")]
 	internal static bool ManagedTypeMap { get; } =
@@ -27,4 +29,9 @@ static class RuntimeFeature
 	[FeatureSwitchDefinition ($"{FeatureSwitchPrefix}{nameof (IsAssignableFromCheck)}")]
 	internal static bool IsAssignableFromCheck { get; } =
 		AppContext.TryGetSwitch ($"{FeatureSwitchPrefix}{nameof (IsAssignableFromCheck)}", out bool isEnabled) ? isEnabled : IsAssignableFromCheckEnabledByDefault;
+
+	[FeatureSwitchDefinition (StartupHookProviderSwitch)]
+	[FeatureGuard (typeof (RequiresUnreferencedCodeAttribute))]
+	internal static bool StartupHookSupport { get; } =
+		AppContext.TryGetSwitch (StartupHookProviderSwitch, out bool isEnabled) ? isEnabled : StartupHookSupportEnabledByDefault;
 }

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets

@@ -131,7 +131,6 @@
     <UseSystemResourceKeys Condition="'$(UseSystemResourceKeys)' == '' and '$(PublishTrimmed)' == 'true'">true</UseSystemResourceKeys>
     <Http3Support Condition="'$(Http3Support)' == ''">false</Http3Support>
     <InvariantGlobalization Condition="'$(InvariantGlobalization)' == ''">false</InvariantGlobalization>
-    <StartupHookSupport Condition="'$(StartupHookSupport)' == ''">false</StartupHookSupport>
     <UseSizeOptimizedLinq Condition="'$(UseSizeOptimizedLinq)' == ''">true</UseSizeOptimizedLinq>
     <UseNativeHttpHandler Condition=" $(AndroidHttpClientHandlerType.Contains ('System.Net.Http.SocketsHttpHandler')) And '$(UseNativeHttpHandler)' == '' ">false</UseNativeHttpHandler>
     <UseNativeHttpHandler Condition="'$(UseNativeHttpHandler)' == ''">true</UseNativeHttpHandler>
@@ -156,6 +155,8 @@
   <!-- Trimmer switches that default to OFF in Release mode -->
   <PropertyGroup Condition=" '$(AndroidApplication)' == 'true' and '$(Optimize)' == 'true' ">
     <DebuggerSupport Condition=" '$(DebuggerSupport)' == '' ">false</DebuggerSupport>
+    <!-- Used for Hot Reload -->
+    <StartupHookSupport Condition=" '$(StartupHookSupport)' == '' ">false</StartupHookSupport>
     <HttpActivityPropagationSupport Condition=" '$(HttpActivityPropagationSupport)' == '' ">false</HttpActivityPropagationSupport>
     <!-- Only set if *not* using $(EnableDiagnostics) -->
     <MetricsSupport Condition=" '$(MetricsSupport)' == '' and '$(AndroidEnableProfiler)' != 'true' ">false</MetricsSupport>

tests/Mono.Android-Tests/Mono.Android-Tests/Mono.Android.NET-Tests.csproj

@@ -49,6 +49,7 @@
     <!-- Trimmer switches required for tests -->
     <JsonSerializerIsReflectionEnabledByDefault Condition="'$(TrimMode)' == 'full'">true</JsonSerializerIsReflectionEnabledByDefault>
     <_DefaultValueAttributeSupport Condition="'$(TrimMode)' == 'full'">true</_DefaultValueAttributeSupport>
+    <StartupHookSupport>true</StartupHookSupport>
   </PropertyGroup>
 
   <ItemGroup Condition=" '$(Configuration)' == 'Debug' ">
@@ -61,13 +62,15 @@
   <ItemGroup>
     <ProjectReference Include="..\..\TestRunner.Core\TestRunner.Core.NET.csproj" />
     <ProjectReference Include="..\..\TestRunner.NUnit\TestRunner.NUnit.NET.csproj" />
+    <ProjectReference Include="..\..\StartupHook\StartupHook.csproj" />
     <ProjectReference Include="..\Java.Interop-Tests\Java.Interop-Tests.NET.csproj" />
     <ProjectReference Include="..\Mono.Android-Test.Library\Mono.Android-Test.Library.NET.csproj" />
     <ProjectReference Include="..\..\..\src\Xamarin.Android.NUnitLite\Xamarin.Android.NUnitLite.NET.csproj" />
   </ItemGroup>
 
   <ItemGroup>
     <TrimmerRootAssembly Include="Java.Interop-Tests" RootMode="All" />
+    <TrimmerRootAssembly Include="StartupHook" RootMode="All" />
     <_AndroidRemapMembers Include="Remaps.xml" />
     <_AndroidRemapMembers Include="IsAssignableFromRemaps.xml" Condition=" '$(_AndroidIsAssignableFromCheck)' == 'false' " />
     <ProguardConfiguration Include="proguard.cfg" />
@@ -103,6 +106,7 @@
     <Compile Include="System\AppDomainTest.cs" />
     <Compile Include="System\AssemblyInformationalVersionAttributeTest.cs" />
     <Compile Include="System\ExceptionTest.cs" />
+    <Compile Include="System\StartupHookTest.cs" />
     <Compile Include="System\TimeZoneTest.cs" />
     <Compile Include="System.Drawing\TypeConverterTest.cs" />
     <Compile Include="System.IO\DirectoryTest.cs" />
@@ -227,6 +231,7 @@
     <RuntimeHostConfigurationOption Include="test_bool"    Value="true" />
     <RuntimeHostConfigurationOption Include="test_integer" Value="42" />
     <RuntimeHostConfigurationOption Include="test_string"  Value="foo" />
+    <RuntimeHostConfigurationOption Include="STARTUP_HOOKS" Value="StartupHook" />
   </ItemGroup>
 
   <ItemGroup Condition=" '$(AndroidPackageFormat)' != 'aab' ">

tests/Mono.Android-Tests/Mono.Android-Tests/System/StartupHookTest.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Reflection;
+using NUnit.Framework;
+
+namespace SystemTests
+{
+	[TestFixture]
+	public class StartupHookTest
+	{
+		[Test]
+		public void IsInitialized ()
+		{
+			var type = Type.GetType ("StartupHook, StartupHook", throwOnError: true);
+			Assert.IsNotNull (type, "StartupHook type should be loaded");
+
+			var property = type.GetProperty ("IsInitialized", BindingFlags.Public | BindingFlags.Static);
+			Assert.IsNotNull (property, "IsInitialized property should exist");
+
+			var value = (bool) property.GetValue (null);
+			Assert.IsTrue (value, "StartupHook.Initialize() should have been called");
+		}
+	}
+}

tests/Mono.Android-Tests/Mono.Android-Tests/env.txt

@@ -1,3 +1,4 @@
 # Environment Variables and system properties
 # debug.mono.log=gref,default
 debug.mono.debug=1
+DOTNET_STARTUP_HOOKS=StartupHook

tests/StartupHook/StartupHook.cs

@@ -0,0 +1,13 @@
+using System;
+
+internal static class StartupHook
+{
+    public static bool IsInitialized { get; private set; }
+
+    public static void Initialize ()
+    {
+        Console.WriteLine ("StartupHook.Initialize() called");
+
+        IsInitialized = true;
+    }
+}

tests/StartupHook/StartupHook.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk" >
+
+  <PropertyGroup>
+    <TargetFramework>$(DotNetAndroidTargetFramework)</TargetFramework>
+    <SupportedOSPlatformVersion>$(AndroidMinimumDotNetApiLevel)</SupportedOSPlatformVersion>
+    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
+    <AndroidGenerateResourceDesigner>false</AndroidGenerateResourceDesigner>
+  </PropertyGroup>
+
+</Project>