[Rgen] Add a factory method that will create the aux variable for handles.

When we interact with nstobjects we need to send the Hanldes as a
parameter and not the managed object. This new method will generated the
aux variable needed to store the handle and use it in the message send
objc method.

Author: mandel-macaque

src/rgen/Microsoft.Macios.Generator/Emitters/BindingSyntaxFactory.ObjCRuntime.cs

@@ -11,8 +11,8 @@
 using Microsoft.Macios.Generator.Attributes;
 using Microsoft.Macios.Generator.DataModel;
 using Microsoft.Macios.Generator.Extensions;
-using TypeInfo = Microsoft.Macios.Generator.DataModel.TypeInfo;
 using static Microsoft.CodeAnalysis.CSharp.SyntaxFactory;
+using TypeInfo = Microsoft.Macios.Generator.DataModel.TypeInfo;
 using Parameter = Microsoft.Macios.Generator.DataModel.Parameter;
 
 namespace Microsoft.Macios.Generator.Emitters;
@@ -167,6 +167,67 @@ static partial class BindingSyntaxFactory {
 			: statement;
 	}
 
+	/// <summary>
+	/// Returns the aux variable for a handle object. This method will do the following:
+	/// 1. Check if the object is nullable or not.
+	/// 2. Use the correct GetHandle method depending on the content of the object.
+	/// </summary>
+	internal static LocalDeclarationStatementSyntax? GetHandleAuxVariable (in Parameter parameter,
+		bool withNullAllowed = false)
+	{
+		if (!parameter.Type.IsNSObject && !parameter.Type.IsINativeObject)
+			return null;
+
+		var variableName = parameter.GetNameForVariableType (Parameter.VariableType.Handle);
+		if (variableName is null)
+			return null;
+		// decide about the factory based on the need of a null check 
+		InvocationExpressionSyntax factoryInvocation;
+		if (withNullAllowed) {
+			// generates: zone!.GetNonNullHandle (nameof (zone));
+			factoryInvocation = InvocationExpression (
+					MemberAccessExpression (SyntaxKind.SimpleMemberAccessExpression,
+						PostfixUnaryExpression (
+							SyntaxKind.SuppressNullableWarningExpression,
+							IdentifierName (parameter.Name)),
+						IdentifierName ("GetNonNullHandle").WithTrailingTrivia (Space)))
+				.WithArgumentList (ArgumentList (
+					SingletonSeparatedList<ArgumentSyntax> (Argument (
+						InvocationExpression (
+								IdentifierName (Identifier (TriviaList (Space), SyntaxKind.NameOfKeyword, "nameof",
+									"nameof",
+									TriviaList (Space))))
+							.WithArgumentList (ArgumentList (
+								SingletonSeparatedList<ArgumentSyntax> (
+									Argument (IdentifierName (parameter.Name)))))))));
+		} else {
+			// generates: zone.GetHandle ();
+			factoryInvocation = InvocationExpression (
+				MemberAccessExpression (SyntaxKind.SimpleMemberAccessExpression,
+					IdentifierName (parameter.Name),
+					IdentifierName ("GetHandle").WithTrailingTrivia (Space)));
+		}
+
+		// generates: variable = {FactoryCall}
+		var declarator = VariableDeclarator (Identifier (variableName))
+			.WithInitializer (EqualsValueClause (factoryInvocation.WithLeadingTrivia (Space)).WithLeadingTrivia (Space));
+		// generates the final statement: 
+		// var x = zone.GetHandle ();
+		// or 
+		// var x = zone!.GetNonNullHandle (nameof (constantValues));
+		return LocalDeclarationStatement (
+			VariableDeclaration (
+				IdentifierName (
+					Identifier (
+						TriviaList (),
+						SyntaxKind.VarKeyword,
+						"var",
+						"var",
+						TriviaList ()))).WithVariables (
+				SingletonSeparatedList (declarator.WithLeadingTrivia (Space))
+			));
+	}
+
 	static string? GetObjCMessageSendMethodName<T> (ExportData<T> exportData,
 		TypeInfo returnType, ImmutableArray<Parameter> parameters, bool isSuper = false, bool isStret = false)
 		where T : Enum

tests/rgen/Microsoft.Macios.Generator.Tests/Emitters/BindingSyntaxFactoryObjCRuntimeTests.cs

@@ -177,8 +177,6 @@ public IEnumerator<object []> GetEnumerator ()
 				new Parameter (0, ReturnTypeForArray ("NSString", isNullable: true), "myParam"),
 				"using var nsa_myParam = myParam is null ? null : NSArray.FromNSObjects (myParam);",
 				true];
-
-
 		}
 
 		IEnumerator IEnumerable.GetEnumerator () => GetEnumerator ();
@@ -196,4 +194,57 @@ void GetNSArrayAuxVariableTests (in Parameter parameter, string? expectedDeclara
 			Assert.Equal (expectedDeclaration, declaration.ToString ());
 		}
 	}
+
+	class TestDataCodeChangesFromClassDeclaration : IEnumerable<object []> {
+		public IEnumerator<object []> GetEnumerator ()
+		{
+			// nsobject type
+			yield return [
+				new Parameter (0, ReturnTypeForNSObject ("MyNSObject"), "myParam"),
+				"var myParam__handle__ = myParam.GetHandle ();",
+				false
+			];
+
+			yield return [
+				new Parameter (0, ReturnTypeForNSObject ("MyNSObject"), "myParam"),
+				"var myParam__handle__ = myParam!.GetNonNullHandle ( nameof (myParam));",
+				true
+			];
+
+			// interface type
+			yield return [
+				new Parameter (0, ReturnTypeForINativeObject ("MyNativeObject"), "myParam"),
+				"var myParam__handle__ = myParam.GetHandle ();",
+				false
+			];
+
+			yield return [
+				new Parameter (0, ReturnTypeForINativeObject ("MyNativeObject"), "myParam"),
+				"var myParam__handle__ = myParam!.GetNonNullHandle ( nameof (myParam));",
+				true
+			];
+
+			// value type
+			yield return [
+				new Parameter (0, ReturnTypeForBool (), "myParam"),
+				null!,
+				false
+			];
+		}
+
+		IEnumerator IEnumerable.GetEnumerator () => GetEnumerator ();
+	}
+
+	[Theory]
+	[ClassData (typeof (TestDataCodeChangesFromClassDeclaration))]
+	void GetHandleAuxVariableTests (in Parameter parameter, string? expectedDeclaration, bool withNullAllowed)
+	{
+		var declaration = GetHandleAuxVariable (parameter, withNullAllowed: withNullAllowed);
+		if (expectedDeclaration is null) {
+			Assert.Null (declaration);
+		} else {
+			Assert.NotNull (declaration);
+			Assert.Equal (expectedDeclaration, declaration.ToString ());
+		}
+	}
 }

tests/rgen/Microsoft.Macios.Generator.Tests/TestDataFactory.cs

@@ -299,4 +299,28 @@ public static TypeInfo ReturnTypeForDelegate (string delegateName)
 				"System.Runtime.Serialization.ISerializable",
 			]
 		};
+
+	public static TypeInfo ReturnTypeForNSObject (string nsObjectName, bool isNullable = false)
+		=> new (
+			name: nsObjectName,
+			isNullable: isNullable,
+			isArray: false
+		) {
+			IsNSObject = true,
+			IsINativeObject = true,
+			Parents = ["Foundation.NSObject", "object"],
+			Interfaces = ["ObjCRuntime.INativeObject"]
+		};
+
+	public static TypeInfo ReturnTypeForINativeObject (string nativeObjectName, bool isNullable = false)
+		=> new (
+			name: nativeObjectName,
+			isNullable: isNullable,
+			isArray: false
+		) {
+			IsNSObject = true,
+			IsINativeObject = true,
+			Parents = ["object"],
+			Interfaces = ["ObjCRuntime.INativeObject"]
+		};
 }