Enable building app extensions with NativeAOT

dotnet/targets/Xamarin.Shared.Sdk.props

@@ -229,7 +229,12 @@
 		<!-- Disable our own assembly IL stripping logic, because ILC does that already -->
 		<EnableAssemblyILStripping>false</EnableAssemblyILStripping>
 
-		<!-- We're using our own native main function when using NativeAOT -->
-		<CustomNativeMain>true</CustomNativeMain>
+		<!--
+			We're using our own native main function when using NativeAOT.
+			This is true for both: managed executables and app extensions that can be class libraries.
+			Since ILC expects to find a managed main function whenever NativeLib=static and CustomNativeMain=true,
+			we are only setting this flag when we are building executables. (Class libraries do not have a managed Main)
+		-->
+		<CustomNativeMain Condition="'$(OutputType)' == 'Exe'">true</CustomNativeMain>
 	</PropertyGroup>
 </Project>

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -591,6 +591,7 @@
 				MtouchFloat32=$(MtouchFloat32)
 				NoWarn=$(_BundlerNoWarn)
 				Optimize=$(_BundlerOptimize)
+				OutputType=$(OutputType)
 				PartialStaticRegistrarLibrary=$(_LibPartialStaticRegistrar)
 				Platform=$(_PlatformName)
 				PlatformAssembly=$(_PlatformAssemblyName).dll

tools/common/Application.cs

@@ -93,6 +93,7 @@ public partial class Application {
 		public HashSet<string> Frameworks = new HashSet<string> ();
 		public HashSet<string> WeakFrameworks = new HashSet<string> ();
 
+		public bool IsClassLibrary;
 		public bool IsExtension;
 		public ApplePlatform Platform { get { return Driver.TargetFramework.Platform; } }
 

tools/common/Target.cs

@@ -891,6 +891,13 @@ void GenerateIOSMain (StringWriter sw, Abi abi)
 			sw.WriteLine ("\treturn rv;");
 			sw.WriteLine ("}");
 
+			// Add an empty __managed__Main function when building class lib app extensions with NativeAOT to workaround static reference to this symbol from nativeaot-bridge.m
+			if (app.IsExtension && App.IsClassLibrary && app.XamarinRuntime == XamarinRuntime.NativeAOT) {
+				sw.WriteLine ();
+				sw.Write ("extern \"C\" int __managed__Main (int argc, const char** argv) { return 0; } ");
+				sw.WriteLine ();
+			}
+
 			string extension_main = null;
 			if (app.Platform == ApplePlatform.WatchOS && app.IsWatchExtension) {
 				// We're building a watch extension, and we have multiple scenarios, depending on the watchOS version we're executing on:

tools/dotnet-linker/LinkerConfiguration.cs

@@ -236,6 +236,9 @@ public static LinkerConfiguration GetInstance (LinkContext context)
 				case "Optimize":
 					user_optimize_flags = value;
 					break;
+				case "OutputType":
+					Application.IsClassLibrary = string.Equals ("Library", value, StringComparison.OrdinalIgnoreCase);
+					break;
 				case "PartialStaticRegistrarLibrary":
 					PartialStaticRegistrarLibrary = value;
 					break;