[RGen] Provide a method that returns the selector for an accessor.

src/rgen/Microsoft.Macios.Generator/DataModel/Accessor.cs

@@ -57,6 +57,31 @@ public Accessor (AccessorKind accessorKind,
 		Modifiers = modifiers;
 	}
 
+	/// <summary>
+	/// Retrieve the selector to be used with the associated property.
+	/// </summary>
+	/// <param name="associatedProperty">The property associated with the accessor.</param>
+	/// <returns>The selector to use for the accessor.</returns>
+	public string? GetSelector (in Property associatedProperty)
+	{
+		// this is not a property but a field, we cannot retrieve a selector.
+		if (!associatedProperty.IsProperty)
+			return null;
+
+		// There are two possible cases, the current accessor has an export attribute, if that
+		// is the case, we will use the selector in that attribute. Otherwise, we have:
+		//
+		// * getter: return the property selector.
+		// * setter: use the registrar code (it has the right logic) to get the setter.
+		if (ExportPropertyData is null) {
+			return Kind == AccessorKind.Getter
+				? associatedProperty.ExportPropertyData.Value.Selector
+				: Registrar.Registrar.CreateSetterSelector (associatedProperty.ExportPropertyData.Value.Selector);
+		}
+
+		return ExportPropertyData.Value.Selector;
+	}
+
 	/// <inheritdoc />
 	public bool Equals (Accessor other)
 	{

src/rgen/Microsoft.Macios.Generator/Microsoft.Macios.Generator.csproj

@@ -34,6 +34,9 @@
         <Compile Include="..\..\bgen\Extensions\PlatformNameExtensions.cs" >
             <Link>external\PlatformNameExtensions.cs</Link>
         </Compile>
+        <Compile Include="..\..\ObjCRuntime\Registrar.core.cs" >
+            <Link>external\Registrar.core.cs</Link>
+        </Compile>
         <Compile Update="Resources.Designer.cs">
           <DesignTime>True</DesignTime>
           <AutoGen>True</AutoGen>

tests/rgen/Microsoft.Macios.Generator.Tests/DataModel/AccessorTests.cs

@@ -5,6 +5,7 @@
 using Microsoft.Macios.Generator.Availability;
 using Microsoft.Macios.Generator.DataModel;
 using Xunit;
+using static Microsoft.Macios.Generator.Tests.TestDataFactory;
 
 namespace Microsoft.Macios.Generator.Tests.DataModel;
 
@@ -308,4 +309,164 @@ public void CompareSameKindSameAttrSameAvailability ()
 		Assert.True (x == y);
 		Assert.False (x != y);
 	}
+
+	[Fact]
+	public void GetSelectorForFieldProperty ()
+	{
+		var property = new Property (
+			name: "MyProperty",
+			returnType: ReturnTypeForString (),
+			symbolAvailability: new (),
+			attributes: [],
+			modifiers: [],
+			accessors: []
+		) {
+			ExportFieldData = new (new ("Constant"), "lib"),
+		};
+
+		var accessor = new Accessor (
+			accessorKind: AccessorKind.Getter,
+			symbolAvailability: new (),
+			exportPropertyData: null,
+			attributes: [
+				new ("First"),
+				new ("Second"),
+			],
+			modifiers: [
+				SyntaxFactory.Token (SyntaxKind.PublicKeyword),
+				SyntaxFactory.Token (SyntaxKind.PrivateKeyword)
+			]);
+
+		Assert.Null (accessor.GetSelector (property));
+	}
+
+	[Fact]
+	public void GetGetterSelectorNoExportData ()
+	{
+		var property = new Property (
+			name: "MyProperty",
+			returnType: ReturnTypeForString (),
+			symbolAvailability: new (),
+			attributes: [],
+			modifiers: [],
+			accessors: []
+		) {
+			ExportPropertyData = new ("label")
+		};
+
+		var accessor = new Accessor (
+			accessorKind: AccessorKind.Getter,
+			symbolAvailability: new (),
+			exportPropertyData: null,
+			attributes: [
+				new ("First"),
+				new ("Second"),
+			],
+			modifiers: [
+				SyntaxFactory.Token (SyntaxKind.PublicKeyword),
+				SyntaxFactory.Token (SyntaxKind.PrivateKeyword)
+			]);
+
+		var selector = accessor.GetSelector (property);
+		Assert.NotNull (selector);
+		Assert.Equal (property.ExportPropertyData.Value.Selector, selector);
+	}
+
+	[Fact]
+	public void GetGetterSelectorExportData ()
+	{
+		var property = new Property (
+			name: "MyProperty",
+			returnType: ReturnTypeForString (),
+			symbolAvailability: new (),
+			attributes: [],
+			modifiers: [],
+			accessors: []
+		) {
+			ExportPropertyData = new ("label")
+		};
+
+		var customSelector = "custom";
+		var accessor = new Accessor (
+			accessorKind: AccessorKind.Getter,
+			symbolAvailability: new (),
+			exportPropertyData: new (customSelector),
+			attributes: [
+				new ("First"),
+				new ("Second"),
+			],
+			modifiers: [
+				SyntaxFactory.Token (SyntaxKind.PublicKeyword),
+				SyntaxFactory.Token (SyntaxKind.PrivateKeyword)
+			]);
+
+		var selector = accessor.GetSelector (property);
+		Assert.NotNull (selector);
+		Assert.Equal (customSelector, selector);
+	}
+
+	[Fact]
+	public void GetSetterSelectorNoExportData ()
+	{
+		var property = new Property (
+			name: "MyProperty",
+			returnType: ReturnTypeForString (),
+			symbolAvailability: new (),
+			attributes: [],
+			modifiers: [],
+			accessors: []
+		) {
+			ExportPropertyData = new ("label")
+		};
+
+		var accessor = new Accessor (
+			accessorKind: AccessorKind.Setter,
+			symbolAvailability: new (),
+			exportPropertyData: null,
+			attributes: [
+				new ("First"),
+				new ("Second"),
+			],
+			modifiers: [
+				SyntaxFactory.Token (SyntaxKind.PublicKeyword),
+				SyntaxFactory.Token (SyntaxKind.PrivateKeyword)
+			]);
+
+		var selector = accessor.GetSelector (property);
+		Assert.NotNull (selector);
+		Assert.Equal ("setLabel:", selector);
+	}
+
+	[Fact]
+	public void GetSetterSelectorExportData ()
+	{
+		var property = new Property (
+			name: "MyProperty",
+			returnType: ReturnTypeForString (),
+			symbolAvailability: new (),
+			attributes: [],
+			modifiers: [],
+			accessors: []
+		) {
+			ExportPropertyData = new ("label")
+		};
+
+		var customSelector = "setCustom:";
+		var accessor = new Accessor (
+			accessorKind: AccessorKind.Setter,
+			symbolAvailability: new (),
+			exportPropertyData: new (customSelector),
+			attributes: [
+				new ("First"),
+				new ("Second"),
+			],
+			modifiers: [
+				SyntaxFactory.Token (SyntaxKind.PublicKeyword),
+				SyntaxFactory.Token (SyntaxKind.PrivateKeyword)
+			]);
+
+		var selector = accessor.GetSelector (property);
+		Assert.NotNull (selector);
+		Assert.Equal (customSelector, selector);
+	}
 }