Proof of Concept: Map Java object to single best managed type and ignore requested targetType

Directory.Build.props

@@ -47,7 +47,7 @@
     <!-- Workaround: https://github.com/dotnet/runtime/issues/55992 -->
     <UseAppHost>False</UseAppHost>
     <AppendTargetFrameworkToOutputPath Condition=" '$(AppendTargetFrameworkToOutputPath)' == '' ">False</AppendTargetFrameworkToOutputPath>
-    <BaseIntermediateOutputPath Condition=" '$(BaseIntermediateOutputPath)' == '' ">obj\</BaseIntermediateOutputPath>
+    <BaseIntermediateOutputPath Condition=" '$(BaseIntermediateOutputPath)' == '' ">$(MSBuildProjectDirectory)\obj\</BaseIntermediateOutputPath>
   </PropertyGroup>
 
   <PropertyGroup>

src/Java.Interop/Java.Interop/JniRuntime.JniValueManager.cs

@@ -307,7 +307,7 @@ static Type GetPeerType ([DynamicallyAccessedMembers (Constructors)] Type type)
 				}
 
 				targetType  = targetType ?? typeof (JavaObject);
-				targetType  = GetPeerType (targetType);
+				targetType = GetPeerType(targetType);
 
 				if (!typeof (IJavaPeerable).IsAssignableFrom (targetType))
 					throw new ArgumentException ($"targetType `{targetType.AssemblyQualifiedName}` must implement IJavaPeerable!", nameof (targetType));
@@ -359,8 +359,8 @@ static Type GetPeerType ([DynamicallyAccessedMembers (Constructors)] Type type)
 					if (!JniTypeSignature.TryParse (jniTypeName, out sig))
 						return null;
 
-					Type? type = GetTypeAssignableTo (sig, targetType);
-					if (type != null) {
+					Type? type = GetBestTypeForSignature (sig);
+					if (type != null && type.IsAssignableTo(targetType)) {
 						var peer = TryCreatePeerInstance (ref reference, transfer, type);
 
 						if (peer != null) {
@@ -379,18 +379,57 @@ static Type GetPeerType ([DynamicallyAccessedMembers (Constructors)] Type type)
 				}
 				JniObjectReference.Dispose (ref klass, JniObjectReferenceOptions.CopyAndDispose);
 
+				// If we have nothing in the hierarchy, assume caller knows best and create targetType
 				return TryCreatePeerInstance (ref reference, transfer, targetType);
 
+
 				[UnconditionalSuppressMessage ("Trimming", "IL2073", Justification = "Types returned here should be preserved via other means.")]
 				[return: DynamicallyAccessedMembers (Constructors)]
-				Type? GetTypeAssignableTo (JniTypeSignature sig, Type targetType)
+				Type? GetBestTypeForSignature (JniTypeSignature sig)
 				{
-					foreach (var t in Runtime.TypeManager.GetTypes (sig)) {
-						if (targetType.IsAssignableFrom (t)) {
-							return t;
+					string[] sdkAssemblyNames = ["Mono.Android", "Java.Base", "Java.Interop"];
+					// Find single best instance
+					Type? best = null;
+					foreach (Type type in Runtime.TypeManager.GetTypes (sig)) {
+						if (best is null) {
+							best = type;
+							continue;
+						}
+						if (type == best)
+							continue;
+						// Types in sdk assemblies should be first in the list
+						if ((uint)Array.IndexOf(sdkAssemblyNames, best.Module.Assembly.GetName ().Name) >
+								(uint)Array.IndexOf(sdkAssemblyNames, type.Module.Assembly.GetName ().Name)) {
+							best = type;
+							continue;
+						}
+						// We found the `Invoker` type *before* the declared type
+						// Fix things up so the abstract type is first, and the `Invoker` is considered a duplicate.
+						if ((type.IsAbstract || type.IsInterface) &&
+								!best.IsAbstract &&
+								!best.IsInterface &&
+								type.IsAssignableFrom (best)) {
+							best = type;
+							continue;
+						}
+
+						// If the type is a derived type of the current best, then it is better
+						if (type.IsAssignableTo(best))
+						{
+							best = type;
+							continue;
+						}
+
+						// we found a generic subclass of a non-generic type
+						if (type.IsGenericType &&
+								!best.IsGenericType &&
+								type.IsAssignableTo (best)) {
+							best = type;
+							continue;
 						}
 					}
-					return null;
+
+					return best;
 				}
 			}
 

src/java-interop/java-interop.targets

@@ -35,13 +35,13 @@
     </PropertyGroup>
 
     <PropertyGroup>
-      <_MonoNativePath>$(NuGetPackageRoot)microsoft.netcore.app.runtime.mono.$(NETCoreSdkRuntimeIdentifier)/$(DotNetRuntimePacksVersion)/runtimes/$(NETCoreSdkRuntimeIdentifier)/native/</_MonoNativePath>
+      <_MonoNativePath>$(NuGetPackageRoot)\microsoft.netcore.app.runtime.mono.$(NETCoreSdkRuntimeIdentifier)/$(DotNetRuntimePacksVersion)/runtimes/$(NETCoreSdkRuntimeIdentifier)/native/</_MonoNativePath>
       <_MonoIncludePath>$(_MonoNativePath)include/mono-2.0</_MonoIncludePath>
       <_DEnableMono>-DENABLE_MONO_INTEGRATION=ON</_DEnableMono>
       <_DEnableOsxArchitectures Condition=" $([MSBuild]::IsOSPlatform ('osx')) ">"-DENABLE_OSX_ARCHITECTURES=$(_CmakeOsxArch)"</_DEnableOsxArchitectures>
       <_DMonoDirs>"-DMONO_INCLUDE_LIST=$(_MonoIncludePath)"</_DMonoDirs>
       <_DJdkDirs>"-DJDK_INCLUDE_LIST=@(JdkIncludePath, ';')"</_DJdkDirs>
-      <_DJni_c>"-DJNI_C_PATH=$(MSBuildThisFileDirectory)$(IntermediateOutputPath)jni.c"</_DJni_c>
+      <_DJni_c>"-DJNI_C_PATH=$(IntermediateOutputPath)jni.c"</_DJni_c>
       <_MonoLinkFlags Condition=" $([MSBuild]::IsOSPlatform ('windows')) " >$(MSBuildThisFileDirectory)coreclr.lib</_MonoLinkFlags>
       <_MonoLinkFlags Condition=" !$([MSBuild]::IsOSPlatform ('windows')) ">-L $(_MonoNativePath) -lcoreclr</_MonoLinkFlags>
       <_DMonoLinkFlags>"-DMONO_LINK_FLAGS=$(_MonoLinkFlags)"</_DMonoLinkFlags>
@@ -71,7 +71,7 @@
       <_Cmake Include="CmakePath=$(CmakePath)" />
       <_Cmake Include="CmakeGenerator=$(CmakeGenerator)" />
       <_Cmake Include="CmakeSourceDir=$(MSBuildThisFileDirectory)" />
-      <_Cmake Include="CmakeBuildDir=$(MSBuildThisFileDirectory)$(IntermediateOutputPath)" />
+      <_Cmake Include="CmakeBuildDir=$(IntermediateOutputPath)" />
       <_Cmake Include="CmakeExtraArgs=$(_ExtraArgs)" />
     </ItemGroup>
     <MSBuild
@@ -86,9 +86,9 @@
 
   <Target Name="_UpdateCoreCLRLib"
       Condition="  $([MSBuild]::IsOSPlatform ('windows'))  And '$(NativeToolchainSupported)' == 'True' "
-      Inputs="coreclr.def"
-      Outputs="corclr.lib">
-    <Exec Command="lib /def:coreclr.def /out:coreclr.lib /machine:X64" />
+      Inputs="$(MSBuildThisFileDirectory)coreclr.def"
+      Outputs="$(MSBuildThisFileDirectory)coreclr.lib">
+    <Exec Command="lib /def:$(MSBuildThisFileDirectory)coreclr.def /out:$(MSBuildThisFileDirectory)coreclr.lib /machine:X64" />
   </Target>
 
   <Target Name="_Clean"

tests/NativeTiming/NativeTiming.targets

@@ -57,7 +57,7 @@
       <_Cmake Include="CmakePath=$(CmakePath)" />
       <_Cmake Include="CmakeGenerator=$(CmakeGenerator)" />
       <_Cmake Include="CmakeSourceDir=$(MSBuildThisFileDirectory)" />
-      <_Cmake Include="CmakeBuildDir=$(MSBuildThisFileDirectory)$(IntermediateOutputPath)%(_NativeTimingLib.Dir)" />
+      <_Cmake Include="CmakeBuildDir=$(IntermediateOutputPath)%(_NativeTimingLib.Dir)" />
       <_Cmake Include="CmakeExtraArgs=$(_JdkDirs)" />
     </ItemGroup>
     <MSBuild