[Java.Interop-Tests] Initial dotnet test support (#801)

Context: dotnet/android#5592

With introductory support for `Java.Interop.dll` on .NET Core via
commit 2a299eb, what about running the unit tests within
`Java.Interop-Tests.dll` on .NET Core?

Update `src/java-interop` so that the `java-interop` native library
is copied to `$(OutputPath)` of referencing projects.  This allows
e.g. `libjava-interop.dylib` to be implicitly copied into the
appropriate output dir, e.g. `bin/TestDebug-netcoreapp3.1`.
Further update `src/java-interop` so that `$(IntermediateOutputPath)`
correctly differs between net472 and netcoreapp3.1 builds, and
generate `jni.c` into `$(IntermediateOutputPath)`.  This ensures that
e.g. `bin/Debug/libjava-interop.dylib` reliably uses Mono on net472,
instead of occasionally/accidentally being the netstandard version.

Update `tests/Java.Interop-Tests` and `tests/TestJVM/TestJVM.csproj`
to multitarget between net472 and netcoreapp3.1.

Update `Java.Runtime.Environment.csproj` to reference
`java-interop.csproj`, which causes all projects which reference
`Java.Runtime.Environment.csproj` to get the `java-interop` native
library copied to the appropriate `$(OutputPath)`.

Update `JreRuntime` to use "dummy" `JniRuntime.JniValueManager` and
`JniRuntime.JniObjectReferenceManager` subclasses when *not* running
under Mono.  This avoids an `ArgumentException` when creating the
`Java.InteropTests.JavaVMFixture` instance used by the unit tests.

Update `tests/TestJVM` to reference
`Xamarin.Android.Tools.AndroidSdk.csproj`, allowing the `TestJVM` type
to use `JdkInfo` to find a JVM to use.  This allows us to avoid a
requirement to set the `JI_JVM_PATH` environment variable in order to
create `TestJVM` instances.

Update `src/Java.Interop` so that generic delegate types are not
marshaled via P/Invoke.  .NET Core doesn't support this.

Update `JniEnvironment.Types.FindClass()` to call
`info.Runtime.GetExceptionForThrowable()` as soon as possible after
calling `JNIEnv::ExceptionClear()`, instead of potentially after
calling `ClassLoader.loadClass()`.  The problem is Java-side stack-
frames: if `info.Runtime.GetExceptionForThrowable()` is delayed, then
the exception created by `info.Runtime.GetExceptionForThrowable()`
only contains the Java message text, but no stack trace, and no
"cause" information.  This meant that when generic delegate types
were still being used, `dotnet test` failures would show:

	java.lang.NoClassDefFoundError: Could not initialize class com.xamarin.interop.CallVirtualFromConstructorDerive

with *no* additional information about *why* it failed.
(It failed because P/Invoke was trying to marshal a generic delegate,
so the `ManagedPeer` static constructor threw an exception, which
was "within" a `static{ManagedPeer.registerNativeMembers(…)}` Java
block, and thus the Java type initializer failed, so nothing worked.)

Update `**/*.java` to remove Version, Culture, and PublicKeyToken
information from the assembly qualified name, for two reasons:

 1. The default Version value appears to differ between
    net472 (0.0.0.0) and netcoreapp3.1 (1.0.0.0).

 2. Wrt dotnet/android#5592, certain "security products"
    believe that the Version number is an *IP address*, and emit a
    warning about "IP Address disclosure".

Since we don't strong-name any of these assemblies (unit tests!)
*or* the expected execution environment is a "self-contained app"
in which you can't have multiple versions of the same assembly
(Xamarin.Android), remove the Version, Culture, and PublicKeyToken
information from these Java Callable Wrappers.

Author: jonpryor

build-tools/scripts/RunNUnitTests.targets

@@ -19,14 +19,6 @@
   </ItemGroup>
   <Target Name="RunTests"
       Outputs="$(_TopDir)\TestResult-%(_TestAssembly.Filename).xml">
-    <ItemGroup>
-      <_JavaInteropNativeLibrary Include="$(_TopDir)\bin\$(Configuration)\libjava-interop.*" />
-    </ItemGroup>
-    <Copy
-        SourceFiles="@(_JavaInteropNativeLibrary)"
-        DestinationFolder="$(_TopDir)\bin\Test$(Configuration)"
-        SkipUnchangedFiles="True"
-    />
     <SetEnvironmentVariable Name="ANDROID_SDK_PATH"      Value="$(AndroidSdkDirectory)" Condition=" '$(AndroidSdkDirectory)' != '' " />
     <SetEnvironmentVariable Name="MONO_TRACE_LISTENER"   Value="Console.Out" />
     <SetEnvironmentVariable Name="JAVA_INTEROP_GREF_LOG" Value="bin\Test$(Configuration)\g-%(_TestAssembly.Filename).txt" />

src/Java.Interop/Java.Interop/JavaProxyObject.cs

@@ -17,9 +17,9 @@ sealed class JavaProxyObject : JavaObject, IEquatable<JavaProxyObject>
 		[JniAddNativeMethodRegistrationAttribute]
 		static void RegisterNativeMembers (JniNativeMethodRegistrationArguments args)
 		{
-			args.Registrations.Add (new JniNativeMethodRegistration ("equals",   "(Ljava/lang/Object;)Z", (Func<IntPtr, IntPtr, IntPtr, bool>)Equals));
-			args.Registrations.Add (new JniNativeMethodRegistration ("hashCode", "()I",                   (Func<IntPtr, IntPtr, int>)GetHashCode));
-			args.Registrations.Add (new JniNativeMethodRegistration ("toString", "()Ljava/lang/String;",  (Func<IntPtr, IntPtr, IntPtr>)ToString));
+			args.Registrations.Add (new JniNativeMethodRegistration ("equals",   "(Ljava/lang/Object;)Z", (EqualsMarshalMethod)Equals));
+			args.Registrations.Add (new JniNativeMethodRegistration ("hashCode", "()I",                   (GetHashCodeMarshalMethod)GetHashCode));
+			args.Registrations.Add (new JniNativeMethodRegistration ("toString", "()Ljava/lang/String;",  (ToStringMarshalMethod)ToString));
 		}
 
 		public override JniPeerMembers JniPeerMembers {
@@ -72,6 +72,7 @@ public override bool Equals (object? obj)
 		}
 
 		// TODO: Keep in sync with the code generated by ExportedMemberBuilder
+		delegate    bool    EqualsMarshalMethod (IntPtr jnienv, IntPtr n_self, IntPtr n_value);
 		static bool Equals (IntPtr jnienv, IntPtr n_self, IntPtr n_value)
 		{
 			var envp = new JniTransition (jnienv);
@@ -91,6 +92,7 @@ static bool Equals (IntPtr jnienv, IntPtr n_self, IntPtr n_value)
 		}
 
 		// TODO: Keep in sync with the code generated by ExportedMemberBuilder
+		delegate    int     GetHashCodeMarshalMethod (IntPtr jnienv, IntPtr n_self);
 		static int GetHashCode (IntPtr jnienv, IntPtr n_self)
 		{
 			var envp = new JniTransition (jnienv);
@@ -107,6 +109,7 @@ static int GetHashCode (IntPtr jnienv, IntPtr n_self)
 			}
 		}
 
+		delegate    IntPtr  ToStringMarshalMethod (IntPtr jnienv, IntPtr n_self);
 		static IntPtr ToString (IntPtr jnienv, IntPtr n_self)
 		{
 			var envp = new JniTransition (jnienv);

src/Java.Interop/Java.Interop/JniEnvironment.Types.cs

@@ -48,29 +48,37 @@ public static unsafe JniObjectReference FindClass (string classname)
 				}
 
 				NativeMethods.java_interop_jnienv_exception_clear (info.EnvironmentPointer);
-				var e   = new JniObjectReference (thrown, JniObjectReferenceType.Local);
-				LogCreateLocalRef (e);
+
+				var findClassThrown     = new JniObjectReference (thrown, JniObjectReferenceType.Local);
+				LogCreateLocalRef (findClassThrown);
+				var pendingException    = info.Runtime.GetExceptionForThrowable (ref findClassThrown, JniObjectReferenceOptions.CopyAndDispose);
 
 				if (info.Runtime.ClassLoader_LoadClass != null) {
 					var java    = info.ToJavaName (classname);
 					var __args  = stackalloc JniArgumentValue [1];
 					__args [0]  = new JniArgumentValue (java);
 
-					IntPtr ignoreThrown;
-					c = NativeMethods.java_interop_jnienv_call_object_method_a (info.EnvironmentPointer, out ignoreThrown, info.Runtime.ClassLoader.Handle, info.Runtime.ClassLoader_LoadClass.ID, (IntPtr) __args);
+					c = NativeMethods.java_interop_jnienv_call_object_method_a (info.EnvironmentPointer, out thrown, info.Runtime.ClassLoader.Handle, info.Runtime.ClassLoader_LoadClass.ID, (IntPtr) __args);
 					JniObjectReference.Dispose (ref java);
-					if (ignoreThrown == IntPtr.Zero) {
-						JniObjectReference.Dispose (ref e);
+					if (thrown == IntPtr.Zero) {
+						(pendingException as IJavaPeerable)?.Dispose ();
 						var r = new JniObjectReference (c, JniObjectReferenceType.Local);
 						JniEnvironment.LogCreateLocalRef (r);
 						return r;
 					}
 					NativeMethods.java_interop_jnienv_exception_clear (info.EnvironmentPointer);
-					NativeMethods.java_interop_jnienv_delete_local_ref (info.EnvironmentPointer, ignoreThrown);
 
+					if (pendingException != null) {
+						NativeMethods.java_interop_jnienv_delete_local_ref (info.EnvironmentPointer, thrown);
+					}
+					else {
+						var loadClassThrown = new JniObjectReference (thrown, JniObjectReferenceType.Local);
+						LogCreateLocalRef (loadClassThrown);
+						pendingException    = info.Runtime.GetExceptionForThrowable (ref loadClassThrown, JniObjectReferenceOptions.CopyAndDispose);
+					}
 				}
 
-				throw info.Runtime.GetExceptionForThrowable (ref e, JniObjectReferenceOptions.CopyAndDispose)!;
+				throw pendingException!;
 #endif  // !FEATURE_JNIENVIRONMENT_JI_PINVOKES
 #if FEATURE_JNIOBJECTREFERENCE_SAFEHANDLES
 				var c       = info.Invoker.FindClass (info.EnvironmentPointer, classname);
@@ -80,25 +88,32 @@ public static unsafe JniObjectReference FindClass (string classname)
 					return new JniObjectReference (c, JniObjectReferenceType.Local);
 				}
 				info.Invoker.ExceptionClear (info.EnvironmentPointer);
-				LogCreateLocalRef (thrown);
+				var findClassThrown     = new JniObjectReference (thrown, JniObjectReferenceType.Local);
+				LogCreateLocalRef (findClassThrown);
+				var pendingException    = info.Runtime.GetExceptionForThrowable (ref findClassThrown, JniObjectReferenceOptions.CopyAndDispose);
 
 				var java    = info.ToJavaName (classname);
 				var __args  = stackalloc JniArgumentValue [1];
 				__args [0]  = new JniArgumentValue (java);
 
-				c                   = info.Invoker.CallObjectMethodA (info.EnvironmentPointer, info.Runtime.ClassLoader.SafeHandle, info.Runtime.ClassLoader_LoadClass.ID, __args);
+				c       = info.Invoker.CallObjectMethodA (info.EnvironmentPointer, info.Runtime.ClassLoader.SafeHandle, info.Runtime.ClassLoader_LoadClass.ID, __args);
 				JniObjectReference.Dispose (ref java);
-				var ignoreThrown    = info.Invoker.ExceptionOccurred (info.EnvironmentPointer);
+				thrown  = info.Invoker.ExceptionOccurred (info.EnvironmentPointer);
 				if (ignoreThrown.IsInvalid) {
-					thrown.Dispose ();
-					JniEnvironment.LogCreateLocalRef (c);
-					return new JniObjectReference (c, JniObjectReferenceType.Local);
+					(pendingException as IJavaPeerable)?.Dispose ();
+					var r   = new JniObjectReference (c, JniObjectReferenceType.Local);
+					JniEnvironment.LogCreateLocalRef (r);
+					return r;
 				}
 				info.Invoker.ExceptionClear (info.EnvironmentPointer);
-				LogCreateLocalRef (ignoreThrown);
-				ignoreThrown.Dispose ();
-				var e   = new JniObjectReference (thrown, JniObjectReferenceType.Local);
-				throw info.Runtime.GetExceptionForThrowable (ref e, JniObjectReferenceOptions.CopyAndDispose);
+				if (pendingException != null) {
+					thrown.Dispose ();
+					throw pendingException;
+				}
+				var loadClassThrown     = new JniObjectReference (thrown, JniObjectReferenceType.Local);
+				LogCreateLocalRef (loadClassThrown);
+				pendingException    = info.Runtime.GetExceptionForThrowable (ref loadClassThrown, JniObjectReferenceOptions.CopyAndDispose);
+				throw pendingException!;
 #endif  // !FEATURE_JNIOBJECTREFERENCE_SAFEHANDLES
 			}
 

src/Java.Interop/Java.Interop/ManagedPeer.cs

@@ -14,18 +14,6 @@ namespace Java.Interop {
 	[JniTypeSignature (JniTypeName)]
 	/* static */ sealed class ManagedPeer : JavaObject {
 
-		delegate void ConstructDelegate (IntPtr jnienv,
-				IntPtr klass,
-				IntPtr n_self,
-				IntPtr n_assemblyQualifiedName,
-				IntPtr n_constructorSignature,
-				IntPtr n_constructorArguments);
-		delegate void RegisterDelegate (IntPtr jnienv,
-				IntPtr klass,
-				IntPtr n_nativeClass,
-				IntPtr n_assemblyQualifiedName,
-				IntPtr n_methods);
-
 		internal const string JniTypeName = "com/xamarin/java_interop/ManagedPeer";
 
 
@@ -37,11 +25,11 @@ static ManagedPeer ()
 					new JniNativeMethodRegistration (
 						"construct",
 						ConstructSignature,
-						(ConstructDelegate) Construct),
+						(ConstructMarshalMethod) Construct),
 					new JniNativeMethodRegistration (
 						"registerNativeMembers",
 						RegisterNativeMembersSignature,
-						(RegisterDelegate) RegisterNativeMembers)
+						(RegisterMarshalMethod) RegisterNativeMembers)
 			);
 		}
 
@@ -62,6 +50,12 @@ public override JniPeerMembers JniPeerMembers {
 		const string ConstructSignature = "(Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;[Ljava/lang/Object;)V";
 
 		// TODO: Keep in sync with the code generated by ExportedMemberBuilder
+		delegate void ConstructMarshalMethod (IntPtr jnienv,
+				IntPtr klass,
+				IntPtr n_self,
+				IntPtr n_assemblyQualifiedName,
+				IntPtr n_constructorSignature,
+				IntPtr n_constructorArguments);
 		static void Construct (
 				IntPtr jnienv,
 				IntPtr klass,
@@ -183,6 +177,11 @@ static Type[] GetParameterTypes (string? signature)
 
 		const   string  RegisterNativeMembersSignature  = "(Ljava/lang/Class;Ljava/lang/String;Ljava/lang/String;)V";
 
+		delegate void RegisterMarshalMethod (IntPtr jnienv,
+				IntPtr klass,
+				IntPtr n_nativeClass,
+				IntPtr n_assemblyQualifiedName,
+				IntPtr n_methods);
 		static void RegisterNativeMembers (
 				IntPtr jnienv,
 				IntPtr klass,

src/Java.Interop/java/com/xamarin/java_interop/internal/JavaProxyObject.java

@@ -8,7 +8,7 @@
 		extends java.lang.Object
 		implements GCUserPeerable
 {
-	static  final   String  assemblyQualifiedName   = "Java.Interop.JavaProxyObject, Java.Interop, Version=0.1.0.0, Culture=neutral, PublicKeyToken=null";
+	static  final   String  assemblyQualifiedName   = "Java.Interop.JavaProxyObject, Java.Interop";
 	static {
 		com.xamarin.java_interop.ManagedPeer.registerNativeMembers (
 				JavaProxyObject.class,

src/Java.Interop/java/com/xamarin/java_interop/internal/JavaProxyThrowable.java

@@ -8,7 +8,7 @@
 		extends java.lang.Error
 		implements GCUserPeerable
 {
-	static  final   String  assemblyQualifiedName   = "Java.Interop.JavaProxyThrowable, Java.Interop, Version=0.1.0.0, Culture=neutral, PublicKeyToken=null";
+	static  final   String  assemblyQualifiedName   = "Java.Interop.JavaProxyThrowable, Java.Interop";
 	static {
 		com.xamarin.java_interop.ManagedPeer.registerNativeMembers (
 				JavaProxyThrowable.class,

src/Java.Runtime.Environment/Java.Interop/JreRuntime.cs

@@ -4,6 +4,7 @@
 using System.Diagnostics;
 using System.IO;
 using System.Linq;
+using System.Reflection;
 using System.Runtime.InteropServices;
 using System.Threading;
 
@@ -44,6 +45,10 @@ public JreRuntimeOptions ()
 				ValueManager            = ValueManager              ?? new MonoRuntimeValueManager ();
 				ObjectReferenceManager  = ObjectReferenceManager    ?? new MonoRuntimeObjectReferenceManager ();
 			}
+			else {
+				ValueManager            = ValueManager              ?? new DummyValueManager ();
+				ObjectReferenceManager  = ObjectReferenceManager    ?? new DummyObjectReferenceManager ();
+			}
 		}
 
 		public JreRuntimeOptions AddOption (string option)
@@ -161,5 +166,52 @@ partial class NativeMethods {
 		[DllImport (JavaInteropLib, CharSet=CharSet.Ansi, CallingConvention=CallingConvention.Cdecl)]
 		internal static extern int java_interop_jvm_create (out IntPtr javavm, out IntPtr jnienv, ref JavaVMInitArgs args);
 	}
+
+	class DummyValueManager : JniRuntime.JniValueManager {
+
+		public override void WaitForGCBridgeProcessing ()
+		{
+		}
+
+		public override void CollectPeers ()
+		{
+		}
+
+		public override void AddPeer (IJavaPeerable reference)
+		{
+		}
+
+		public override void RemovePeer (IJavaPeerable reference)
+		{
+		}
+
+		public override void FinalizePeer (IJavaPeerable reference)
+		{
+		}
+
+		public override List<JniSurfacedPeerInfo> GetSurfacedPeers ()
+		{
+			return null;
+		}
+
+		public override IJavaPeerable PeekPeer (global::Java.Interop.JniObjectReference reference)
+		{
+			return null;
+		}
+
+		public override void ActivatePeer (IJavaPeerable self, JniObjectReference reference, ConstructorInfo cinfo, object [] argumentValues)
+		{
+		}
+	}
+
+	class DummyObjectReferenceManager : JniRuntime.JniObjectReferenceManager {
+		public override int GlobalReferenceCount {
+			get {return 0;}
+		}
+
+		public override int WeakGlobalReferenceCount {
+			get {return 0;}
+		}
+	}
 }
 

src/Java.Runtime.Environment/Java.Runtime.Environment.csproj

@@ -13,6 +13,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\Java.Interop\Java.Interop.csproj" />
+    <ProjectReference Include="..\..\src\java-interop\java-interop.csproj" ReferenceOutputAssembly="false" />
   </ItemGroup>
 
   <ItemGroup>

src/java-interop/java-interop.csproj

@@ -39,7 +39,7 @@
   </ItemDefinitionGroup>
 
   <ItemGroup>
-    <ClCompile Include="jni.c" />
+    <ClCompile Include="$(IntermediateOutputPath)jni.c" />
     <ClCompile Include="java-interop.cc" />
     <ClCompile Include="java-interop-dlfcn.cc" />
     <ClCompile Include="java-interop-jvm.cc" />

src/java-interop/java-interop.targets

@@ -2,21 +2,33 @@
 <Project>
   <Target Name="BuildJni_c"
       Inputs="$(_JNIEnvGenPath)"
-      Outputs="jni.c">
+      Outputs="$(IntermediateOutputPath)jni.c">
     <MakeDir Directories="$(OutputPath)" />
-    <Exec Command="$(_RunJNIEnvGen) jni.g.cs jni.c" />
+    <Exec Command="$(_RunJNIEnvGen) $(IntermediateOutputPath)jni.g.cs $(IntermediateOutputPath)jni.c" />
   </Target>
 
   <PropertyGroup>
     <_MacLib>$(OutputPath)/lib$(OutputName).dylib</_MacLib>
     <_UnixLib>$(OutputPath)/lib$(OutputName).so</_UnixLib>
   </PropertyGroup>
 
+  <ItemGroup Condition=" '$(OS)' != 'Windows_NT' And Exists ('/Library/Frameworks/') ">
+    <None Include="$(_MacLib)">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
+  <ItemGroup Condition=" '$(OS)' != 'Windows_NT' And !Exists ('/Library/Frameworks/') ">
+    <None Include="$(_UnixLib)">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
   <ItemDefinitionGroup>
     <ClCompile>
       <PreprocessorDefinitions>$([MSBuild]::Unescape($(DefineSymbols.Replace(' ', ';'))))</PreprocessorDefinitions>
       <AdditionalIncludeDirectories>$([MSBuild]::Unescape($(_MonoIncludePath)));$([MSBuild]::Unescape($(_JdkIncludePath)))</AdditionalIncludeDirectories>
-      <Obj Condition=" '$(OS)' != 'Windows_NT' ">obj/$(Configuration)/%(Filename).o</Obj>
+      <Obj Condition=" '$(OS)' != 'Windows_NT' ">$(IntermediateOutputPath)/%(Filename).o</Obj>
     </ClCompile>
   </ItemDefinitionGroup>
 
@@ -25,7 +37,7 @@
       DependsOnTargets="BuildJni_c"
       Inputs="@(ClCompile);@(ClInclude)"
       Outputs="%(ClCompile.Obj)">
-    <MakeDir Directories="obj\$(Configuration)" />
+    <MakeDir Directories="$(IntermediateOutputPath)" />
     <ItemGroup>
       <_Cl Include="@(ClCompile)">
         <Compiler Condition=" '%(Extension)' == '.c' ">gcc -std=c99 -fPIC</Compiler>
@@ -86,7 +98,6 @@
 
   <Target Name="Clean">
     <RemoveDir Directories="obj" />
-    <Delete Files="jni.c" />
     <Delete
         Files="$(_MacLib);$(_UnixLib)"
         Condition=" '$(OS)' != 'Windows_NT' "