[Rgen] Provide the needed code to parse notification attrs.

src/rgen/Microsoft.Macios.Transformer/Attributes/NotificationData.cs

@@ -0,0 +1,97 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.CodeAnalysis;
+
+namespace Microsoft.Macios.Transformer.Attributes;
+
+readonly record struct NotificationData {
+
+	/// <summary>
+	/// Diff the constructor used in the bindings.
+	/// </summary>
+	internal enum ConstructorType {
+		NotificationType,
+		NotificationCenter,
+		All
+	}
+
+	public string? Type { get; init; }
+	public string? NotificationCenter { get; init; }
+
+	public NotificationData (string? data, ConstructorType constructorType)
+	{
+		if (constructorType == ConstructorType.NotificationType) {
+			Type = data;
+		} else {
+			NotificationCenter = data;
+		}
+	}
+
+	public NotificationData (string? type, string? notificationCenter)
+	{
+		Type = type;
+		NotificationCenter = notificationCenter;
+	}
+
+	public static bool TryParse (AttributeData attributeData,
+		[NotNullWhen (true)] out NotificationData? data)
+	{
+		data = null;
+		var count = attributeData.ConstructorArguments.Length;
+		ConstructorType constructorType = ConstructorType.NotificationType;
+		string? notificationType = null;
+		string? notificationCenter = null;
+
+		switch (count) {
+		case 0:
+			break;
+		case 1:
+			// we have to diff constructors that take a single parameter, either a string or a type
+			if (attributeData.ConstructorArguments [0].Value! is string notificationCenterValue) {
+				constructorType = ConstructorType.NotificationCenter;
+				notificationCenter = notificationCenterValue;
+			} else {
+				constructorType = ConstructorType.NotificationType;
+				notificationType = ((INamedTypeSymbol) attributeData.ConstructorArguments [0].Value!).ToDisplayString ();
+			}
+			break;
+		case 2:
+			constructorType = ConstructorType.All;
+			notificationType = ((INamedTypeSymbol) attributeData.ConstructorArguments [0].Value!).ToDisplayString ();
+			notificationCenter = (string?) attributeData.ConstructorArguments [1].Value!;
+			break;
+		default:
+			// 0 should not be an option..
+			return false;
+		}
+
+		if (attributeData.NamedArguments.Length == 0) {
+			data = constructorType switch {
+				ConstructorType.NotificationCenter => new (notificationCenter, ConstructorType.NotificationCenter),
+				ConstructorType.NotificationType => new (notificationType, ConstructorType.NotificationType),
+				_ => new (notificationType, notificationCenter)
+			};
+			return true;
+		}
+
+		foreach (var (argumentName, value) in attributeData.NamedArguments) {
+			switch (argumentName) {
+			case "Type":
+				notificationType = ((INamedTypeSymbol) value.Value!).ToDisplayString ();
+				break;
+			case "NotificationCenter":
+				notificationCenter = (string) value.Value!;
+				break;
+			default:
+				data = null;
+				return false;
+			}
+		}
+
+		data = new (notificationType, notificationCenter);
+		return true;
+	}
+
+}

src/rgen/Microsoft.Macios.Transformer/AttributesNames.cs

@@ -184,6 +184,13 @@ static class AttributesNames {
 	[BindingFlag (AttributeTargets.Method)]
 	public const string NoMethodAttribute = "NoMethodAttribute";
 
+	/// <summary>
+	/// When applied, flags the [Flags] as a notification and generates the
+	/// code to strongly type the notification.
+	/// </summary>
+	[BindingAttribute(typeof(NotificationData), AttributeTargets.Property)]
+	public const string NotificationAttribute = "NotificationAttribute";
+
 	public const string NoTVAttribute = "NoTVAttribute";
 	public const string NoiOSAttribute = "NoiOSAttribute";
 

tests/rgen/Microsoft.Macios.Transformer.Tests/Attributes/BindDataTests.cs

@@ -2,9 +2,7 @@
 // Licensed under the MIT License.
 
 using System.Collections;
-using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.Macios.Generator.Extensions;
 using Microsoft.Macios.Transformer.Attributes;
 using Xamarin.Tests;
 using Xamarin.Utils;

tests/rgen/Microsoft.Macios.Transformer.Tests/Attributes/NotificationDataTests.cs

@@ -0,0 +1,112 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System.Collections;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.Macios.Transformer.Attributes;
+using Xamarin.Tests;
+using Xamarin.Utils;
+
+namespace Microsoft.Macios.Transformer.Tests.Attributes;
+
+public class NotificationDataTests : AttributeParsingTestClass {
+
+	class TestDataTryCreate : IEnumerable<object []> {
+		public IEnumerator<object []> GetEnumerator ()
+		{
+			const string path = "/some/random/path.cs";
+
+			// simple notification
+			const string simpleNotification = @"
+using System;
+using Foundation;
+using ObjCRuntime;
+using UIKit;
+
+namespace Test;
+
+[NoMacCatalyst]
+[BaseType (typeof (NSView))]
+partial interface NSSplitView {
+		[Notification]
+		[Field (""NSSplitViewWillResizeSubviewsNotification"")]
+		NSString NSSplitViewWillResizeSubviewsNotification { get; }
+}
+";
+			yield return [(Source: simpleNotification, Path: path), new NotificationData (null, null)];
+
+			// notification type
+			const string notificationWithType = @"
+using System;
+using Foundation;
+using ObjCRuntime;
+using UIKit;
+
+namespace Test;
+
+class MyNotification {}
+
+[NoMacCatalyst]
+[BaseType (typeof (NSView))]
+partial interface NSSplitView {
+		[Notification (typeof (MyNotification))]
+		[Field (""NSSplitViewWillResizeSubviewsNotification"")]
+		NSString NSSplitViewWillResizeSubviewsNotification { get; }
+}
+";
+
+			yield return [(Source: notificationWithType, Path: path), new NotificationData ("Test.MyNotification", null)];
+
+			// notification center
+			const string notificationWithCenter = @"
+using System;
+using Foundation;
+using ObjCRuntime;
+using UIKit;
+
+namespace Test;
+
+class MyNotification {}
+
+[NoMacCatalyst]
+[BaseType (typeof (NSView))]
+partial interface NSSplitView {
+		[Notification (""SharedWorkspace.NotificationCenter"")]
+		[Field (""NSSplitViewWillResizeSubviewsNotification"")]
+		NSString NSSplitViewWillResizeSubviewsNotification { get; }
+}
+";
+			yield return [(Source: notificationWithCenter, Path: path), new NotificationData (null, "SharedWorkspace.NotificationCenter")];
+
+			// both
+			const string notificationWithBoth = @"
+using System;
+using Foundation;
+using ObjCRuntime;
+using UIKit;
+
+namespace Test;
+
+class MyNotification {}
+
+[NoMacCatalyst]
+[BaseType (typeof (NSView))]
+partial interface NSSplitView {
+		[Notification (typeof (MyNotification), ""SharedWorkspace.NotificationCenter"")]
+		[Field (""NSSplitViewWillResizeSubviewsNotification"")]
+		NSString NSSplitViewWillResizeSubviewsNotification { get; }
+}
+";
+			yield return [(Source: notificationWithBoth, Path: path), new NotificationData ("Test.MyNotification", "SharedWorkspace.NotificationCenter")];
+		}
+
+		IEnumerator IEnumerable.GetEnumerator () => GetEnumerator ();
+	}
+
+	[Theory]
+	[AllSupportedPlatformsClassData<TestDataTryCreate>]
+	void TryCreateTests (ApplePlatform platform, (string Source, string Path) source,
+		NotificationData expectedData)
+		=> AssertTryCreate<NotificationData, PropertyDeclarationSyntax> (platform, source, AttributesNames.NotificationAttribute,
+			expectedData, NotificationData.TryParse, lastOrDefault: true);
+}