Fix UCO constructor wrappers to include full JNI parameter list

The UCO constructor wrapper signature must match the JNI native method
signature (jnienv + self + constructor params) for correct ABI.
Previously it only accepted (IntPtr, IntPtr), causing a calling convention
mismatch when JNI dispatches constructors with parameters.

The body still calls ActivateInstance(self, typeof(T)) — the constructor
params are consumed but not forwarded, since peer activation uses the
(IntPtr, JniHandleOwnership) activation ctor, not the user constructor.

Author: simonrozsival

src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/Model/TypeMapAssemblyData.cs

@@ -132,6 +132,8 @@ sealed class UcoMethodData
 
 /// <summary>
 /// An [UnmanagedCallersOnly] static wrapper for a constructor callback.
+/// Signature must match the full JNI native method signature (jnienv + self + ctor params)
+/// so the ABI is correct when JNI dispatches the call.
 /// Body: TrimmableNativeRegistration.ActivateInstance(self, typeof(TargetType)).
 /// </summary>
 sealed class UcoConstructorData

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

@@ -493,19 +493,25 @@ MethodDefinitionHandle EmitUcoConstructor (MetadataBuilder metadata, BlobBuilder
 	{
 		var userTypeRef = ResolveTypeRef (metadata, uco.TargetType);
 
-		// UCO constructor wrappers always take exactly (IntPtr jnienv, IntPtr self) regardless
-		// of the actual JNI constructor signature. The JNI parameters are not forwarded —
-		// ActivateInstance only needs the jobject handle to create the managed peer.
-		// The correct JNI signature is still used in RegisterNatives so the JNI runtime
-		// dispatches to this wrapper for the right constructor overload.
+		// UCO constructor wrappers must match the JNI native method signature exactly.
+		// The Java JCW declares e.g. "private native void nctor_0(Context p0)" and calls
+		// it with arguments. JNI dispatches with (JNIEnv*, jobject, <ctor params...>),
+		// so the wrapper signature must include all parameters to match the ABI.
+		// Only jnienv (arg 0) and self (arg 1) are used — the constructor parameters
+		// are not forwarded because ActivateInstance creates the managed peer using the
+		// activation ctor (IntPtr, JniHandleOwnership), not the user-visible constructor.
+		var jniParams = JniSignatureHelper.ParseParameterTypes (uco.JniSignature);
+		int paramCount = 2 + jniParams.Count;
 
 		var handle = EmitBody (metadata, ilBuilder, uco.WrapperName,
 			MethodAttributes.Public | MethodAttributes.Static | MethodAttributes.HideBySig,
-			sig => sig.MethodSignature ().Parameters (2,
+			sig => sig.MethodSignature ().Parameters (paramCount,
 				rt => rt.Void (),
 				p => {
-					p.AddParameter ().Type ().IntPtr ();
-					p.AddParameter ().Type ().IntPtr ();
+					p.AddParameter ().Type ().IntPtr (); // jnienv
+					p.AddParameter ().Type ().IntPtr (); // self
+					for (int j = 0; j < jniParams.Count; j++)
+						JniSignatureHelper.EncodeClrType (p.AddParameter ().Type (), jniParams [j]);
 				}),
 			encoder => {
 				encoder.LoadArgument (1); // self

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

@@ -1550,7 +1550,7 @@ public void FullPipeline_CustomView_HasConstructorAndMethodWrappers ()
 		}
 
 		[Fact]
-		public void FullPipeline_CustomView_UcoConstructorHasExactlyTwoParams ()
+		public void FullPipeline_CustomView_UcoConstructorMatchesJniSignature ()
 		{
 			var peer = FindFixtureByJavaName ("my/app/CustomView");
 			var model = BuildModel (new [] { peer }, "CtorSigTest");
@@ -1574,12 +1574,22 @@ public void FullPipeline_CustomView_UcoConstructorHasExactlyTwoParams ()
 					.ToList ();
 
 				Assert.NotEmpty (ucoCtors);
+
+				// Match each UCO constructor to its model data to verify param count
 				foreach (var uco in ucoCtors) {
-					// UCO constructor wrappers always take exactly 2 params (IntPtr jnienv, IntPtr self)
+					var name = reader.GetString (uco.Name);
+					var modelUco = model.ProxyTypes
+						.SelectMany (p => p.UcoConstructors)
+						.First (u => u.WrapperName == name);
+
+					// UCO constructor signature must include jnienv + self + JNI params
+					int expectedJniParams = JniSignatureHelper.ParseParameterTypes (modelUco.JniSignature).Count;
+					int expectedTotal = 2 + expectedJniParams;
+
 					var sig = reader.GetBlobReader (uco.Signature);
 					var header = sig.ReadSignatureHeader ();
 					int paramCount = sig.ReadCompressedInteger ();
-					Assert.Equal (2, paramCount);
+					Assert.Equal (expectedTotal, paramCount);
 				}
 			} finally {
 				CleanUpDir (outputPath);