[TrimmableTypeMap] Reject open generic JNI construction

src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/TypeMapAssemblyEmitter.cs

@@ -976,16 +976,20 @@ MethodDefinitionHandle EmitUcoConstructor (UcoConstructorData uco, JavaPeerProxy
 					JniSignatureHelper.EncodeClrType (p.AddParameter ().Type (), jniParams [j]);
 			});
 
-		// Open generic types can't be activated — emit a no-op UCO.
+		// Open generic types can't be activated because Java construction cannot provide the type arguments.
 		if (proxy.IsGenericDefinition) {
-			var noopHandle = _pe.EmitBody (uco.WrapperName,
+			var openGenericHandle = _pe.EmitBody (uco.WrapperName,
 				MethodAttributes.Public | MethodAttributes.Static | MethodAttributes.HideBySig,
 				encodeSig,
-				encoder => {
-					encoder.OpCode (ILOpCode.Ret);
-				});
-			AddUnmanagedCallersOnlyAttribute (noopHandle);
-			return noopHandle;
+				(encoder, cfb) => EmitUcoConstructorBodyWithMarshal (encoder, cfb, enc => {
+					enc.LoadString (_pe.Metadata.GetOrAddUserString ("Constructing instances of generic types from Java is not supported, as the type parameters cannot be determined."));
+					enc.OpCode (ILOpCode.Newobj);
+					enc.Token (_notSupportedExceptionCtorRef);
+					enc.OpCode (ILOpCode.Throw);
+				}),
+				EncodeUcoConstructorLocals_Standard);
+			AddUnmanagedCallersOnlyAttribute (openGenericHandle);
+			return openGenericHandle;
 		}
 
 		MethodDefinitionHandle handle;

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/FixtureTestBase.cs

@@ -143,4 +143,32 @@ private protected static List<string> GetMemberRefNames (MetadataReader reader)
 			.Select (m => reader.GetString (m.Name))
 			.ToList ();
 
+	/// <summary>
+	/// Returns true if the IL byte stream contains a Call (0x28) or Callvirt (0x6F) instruction
+	/// whose metadata token matches <paramref name="token"/>.
+	/// </summary>
+	private protected static bool ILContainsCallToken (byte[] ilBytes, int token)
+	{
+		return ILContainsOpcodeToken (ilBytes, token, (byte) ILOpCode.Call, (byte) ILOpCode.Callvirt);
+	}
+
+	private protected static bool ILContainsNewobjToken (byte[] ilBytes, int token)
+	{
+		return ILContainsOpcodeToken (ilBytes, token, (byte) ILOpCode.Newobj);
+	}
+
+	static bool ILContainsOpcodeToken (byte[] ilBytes, int token, params byte[] opcodes)
+	{
+		byte t0 = (byte)(token & 0xFF);
+		byte t1 = (byte)((token >> 8) & 0xFF);
+		byte t2 = (byte)((token >> 16) & 0xFF);
+		byte t3 = (byte)((token >> 24) & 0xFF);
+		for (int i = 0; i < ilBytes.Length - 4; i++) {
+			if (opcodes.Contains (ilBytes [i]) &&
+			    ilBytes [i + 1] == t0 && ilBytes [i + 2] == t1 &&
+			    ilBytes [i + 3] == t2 && ilBytes [i + 4] == t3)
+				return true;
+		}
+		return false;
+	}
 }

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/TypeMapAssemblyGeneratorTests.cs

@@ -1173,28 +1173,61 @@ public void Generate_UcoConstructor_JiStyle_HasExceptionRegions ()
 	}
 
 	[Fact]
-	public void Generate_UcoConstructor_GenericDefinition_NoExceptionRegions ()
+	public void Generate_UcoConstructor_GenericDefinition_ThrowsWithMarshalMethodPattern ()
 	{
-		// Open-generic UCO constructors are no-ops and must NOT have exception regions
-		// (a single 'ret' is emitted with no surrounding try/catch/finally).
-		var peers = ScanFixtures ();
-		var generic = peers.First (p => p.JavaName == "my/app/GenericHolder");
-		Assert.True (generic.IsGenericDefinition);
+		// Open-generic UCO constructors throw inside the same marshal-method wrapper used
+		// by normal UCO constructors, so the exception is surfaced through
+		// JniRuntime.OnUserUnhandledException instead of crossing the JNI boundary.
+		var generic = MakeAcwPeer ("test/GenericHolder", "Test.GenericHolder`1", "TestAsm") with {
+			IsGenericDefinition = true,
+		};
 
 		using var stream = GenerateAssembly (new [] { generic }, "GenericUcoCtorTest");
 		using var pe = new PEReader (stream);
 		var reader = pe.GetMetadataReader ();
 
 		var nctorMethodHandle = FindNctorUcoMethod (reader);
+		Assert.False (nctorMethodHandle.IsNil, "Open-generic ACWs should emit a throwing nctor_*_uco method");
 
-		if (!nctorMethodHandle.IsNil) {
-			// If a nctor_*_uco method exists for the generic type, it must be a no-op (no exception regions).
-			var nctorMethod = reader.GetMethodDefinition (nctorMethodHandle);
-			var body = pe.GetMethodBody (nctorMethod.RelativeVirtualAddress);
-			Assert.NotNull (body);
-			Assert.Empty (body.ExceptionRegions);
-		}
-		// Open-generic types do not get a nctor_*_uco wrapper — no UCO ctors for generics.
+		var nctorMethod = reader.GetMethodDefinition (nctorMethodHandle);
+		var body = pe.GetMethodBody (nctorMethod.RelativeVirtualAddress);
+		Assert.NotNull (body);
+
+		var regions = body.ExceptionRegions;
+		Assert.True (regions.Length >= 2,
+			$"Open-generic UCO constructor should have at least 2 exception regions, found {regions.Length}");
+		Assert.Contains (regions, r => r.Kind == ExceptionRegionKind.Catch);
+		Assert.Contains (regions, r => r.Kind == ExceptionRegionKind.Finally);
+
+		var typeNames = GetTypeRefNames (reader);
+		Assert.Contains ("NotSupportedException", typeNames);
+
+		var ilBytes = body.GetILBytes ();
+		Assert.NotNull (ilBytes);
+		var memberRefHandles = Enumerable.Range (1, reader.GetTableRowCount (TableIndex.MemberRef))
+			.Select (i => MetadataTokens.MemberReferenceHandle (i))
+			.ToList ();
+		var notSupportedExceptionCtorHandle = memberRefHandles.First (h => {
+			var member = reader.GetMemberReference (h);
+			if (reader.GetString (member.Name) != ".ctor" || member.Parent.Kind != HandleKind.TypeReference) {
+				return false;
+			}
+
+			var parent = reader.GetTypeReference ((TypeReferenceHandle) member.Parent);
+			return reader.GetString (parent.Name) == "NotSupportedException";
+		});
+		var beginHandle = memberRefHandles.First (h => reader.GetString (reader.GetMemberReference (h).Name) == "BeginMarshalMethod");
+		var endHandle = memberRefHandles.First (h => reader.GetString (reader.GetMemberReference (h).Name) == "EndMarshalMethod");
+		var exHandle = memberRefHandles.First (h => reader.GetString (reader.GetMemberReference (h).Name) == "OnUserUnhandledException");
+		int notSupportedExceptionCtorToken = MetadataTokens.GetToken (notSupportedExceptionCtorHandle);
+		int beginToken = MetadataTokens.GetToken (beginHandle);
+		int endToken = MetadataTokens.GetToken (endHandle);
+		int exToken = MetadataTokens.GetToken (exHandle);
+		Assert.True (ILContainsNewobjToken (ilBytes, notSupportedExceptionCtorToken), "open-generic nctor_*_uco IL should construct NotSupportedException");
+		Assert.True (ilBytes.Contains ((byte) ILOpCode.Throw), "open-generic nctor_*_uco IL should throw");
+		Assert.True (ILContainsCallToken (ilBytes, beginToken), "open-generic nctor_*_uco IL should call BeginMarshalMethod");
+		Assert.True (ILContainsCallToken (ilBytes, endToken), "open-generic nctor_*_uco IL should call EndMarshalMethod");
+		Assert.True (ILContainsCallToken (ilBytes, exToken), "open-generic nctor_*_uco IL should call OnUserUnhandledException");
 	}
 
 	[Fact]

tests/Mono.Android-Tests/Mono.Android-Tests/Java.Interop/JnienvTest.cs

@@ -121,7 +121,6 @@ public void InvokingNullInstanceDoesNotCrashDalvik ()
 			}
 		}
 
-		// TODO: https://github.com/dotnet/android/issues/11170 — open generic creation should throw but succeeds under trimmable typemap
 		[Test]
 		public void NewOpenGenericTypeThrows ()
 		{

tests/Mono.Android-Tests/Mono.Android-Tests/Xamarin.Android.RuntimeTests/NUnitInstrumentation.cs

@@ -67,12 +67,6 @@ protected NUnitInstrumentation(IntPtr handle, JniHandleOwnership transfer)
                     "Java.InteropTests.JniPeerMembersTests.ReplacementTypeUsedForMethodLookup",
                     "Java.InteropTests.JniPeerMembersTests.ReplaceStaticMethodName",
 
-                    // net.dot.jni.test.GenericHolder Java class not in APK
-                    "Java.InteropTests.JniTypeManagerTests.CannotCreateGenericHolderFromJava",
-
-                    // Open generic type handling differs from non-trimmable
-                    "Java.InteropTests.JnienvTest.NewOpenGenericTypeThrows",
-
                     // Throwable subclass registration
                     "Java.InteropTests.JnienvTest.ActivatedDirectThrowableSubclassesShouldBeRegistered",