[monodroid] typemaps may need to load assemblies

.gitmodules

@@ -9,7 +9,7 @@
 [submodule "external/Java.Interop"]
     path = external/Java.Interop
     url = https://github.com/xamarin/java.interop.git
-    branch = main
+    branch = dev/jonp/ji-typemap-support
 [submodule "external/lz4"]
     path = external/lz4
     url = https://github.com/xamarin/lz4

src/Xamarin.Android.Build.Tasks/Utilities/XAJavaTypeScanner.cs

@@ -77,7 +77,7 @@ public List<JavaType> GetJavaTypes (ICollection<ITaskItem> inputAssemblies, XAAs
 
 	void AddJavaType (TypeDefinition type, Dictionary<string, TypeData> types, AndroidTargetArch arch)
 	{
-		if (type.IsSubclassOf ("Java.Lang.Object", cache) || type.IsSubclassOf ("Java.Lang.Throwable", cache) || (type.IsInterface && type.ImplementsInterface ("Java.Interop.IJavaPeerable", cache))) {
+		if (type.ImplementsInterface ("Java.Interop.IJavaPeerable", cache)) {
 			// For subclasses of e.g. Android.App.Activity.
 			string typeName = type.GetPartialAssemblyQualifiedName (cache);
 			if (!types.TryGetValue (typeName, out TypeData typeData)) {

src/monodroid/jni/embedded-assemblies.cc

@@ -695,6 +695,20 @@ EmbeddedAssemblies::typemap_java_to_managed (hash_t hash, const MonoString *java
 
 	if (module->image == nullptr) {
 		module->image = mono_image_loaded (module->assembly_name);
+
+		if (module->image == nullptr) {
+			log_debug (LOG_ASSEMBLY, "typemap: assembly '%s' hasn't been loaded yet, attempting a full load", module->assembly_name);
+
+			// Trigger MonoVM's machinery to load an image. This will involve calling us back to find, uncompress (if
+            // necessary) and load the assembly from whatever storage the app uses.
+			MonoImageOpenStatus status{};
+			module->image = mono_image_open (module->assembly_name, &status);
+
+			if (status != MonoImageOpenStatus::MONO_IMAGE_OK) {
+				log_warn (LOG_ASSEMBLY, "typemap: failed to load managed assembly image '%s'. %s", module->assembly_name, mono_image_strerror (status));
+			}
+		}
+
 		if (module->image == nullptr) {
 			log_error (LOG_ASSEMBLY, "typemap: unable to load assembly '%s' when looking up managed type corresponding to Java type '%s'", module->assembly_name, to_utf8 (java_type_name).get ());
 			return nullptr;