Add AlsoBroadcastChangeAttribute type

Author: Sergio0694

CommunityToolkit.Mvvm/ComponentModel/Attributes/AlsoBroadcastChangeAttribute.cs

@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Diagnostics;
+
+namespace CommunityToolkit.Mvvm.ComponentModel;
+
+/// <summary>
+/// An attribute that can be used to support <see cref="ObservablePropertyAttribute"/> in generated properties, when applied to fields
+/// contained in a type that is either inheriting from <see cref="ObservableRecipient"/>, or annotated with <see cref="ObservableRecipientAttribute"/>.
+/// When this attribute is used, the generated property setter will also call <see cref="ObservableRecipient.Broadcast{T}(T, T, string?)"/>.
+/// This allows generated properties to opt-in into broadcasting behavior without having to fallback into a full explicit observable property.
+/// <para>
+/// This attribute can be used as follows:
+/// <code>
+/// partial class MyViewModel : ObservableRecipient
+/// {
+///     [ObservableProperty]
+///     [AlsoBroadcastChange]
+///     private string username;
+/// }
+/// </code>
+/// </para>
+/// And with this, code analogous to this will be generated:
+/// <code>
+/// partial class MyViewModel
+/// {
+///     public string Username
+///     {
+///         get => username;
+///         set => SetProperty(ref username, value, broadcast: true);
+///     }
+/// }
+/// </code>
+/// </summary>
+[AttributeUsage(AttributeTargets.Field, AllowMultiple = false, Inherited = false)]
+[Conditional("MVVMTOOLKIT_KEEP_SOURCE_GENERATOR_ATTRIBUTES")]
+public sealed class AlsoBroadcastChangeAttribute : Attribute
+{
+}

tests/CommunityToolkit.Mvvm.KeepSourceGeneratorAttributes.UnitTests/Test_SourceGeneratorAttributes.cs

@@ -21,7 +21,7 @@ public void Test_AttributeMetadata()
         Assert.Fail();
 #endif
         Assert.AreEqual(3, typeof(TestModel).GetCustomAttributes().Count(a => a.GetType().FullName!.Contains("CommunityToolkit.Mvvm")));
-        Assert.AreEqual(3, typeof(TestModel).GetField(nameof(TestModel.name))!.GetCustomAttributes().Count(a => a.GetType().FullName!.Contains("CommunityToolkit.Mvvm")));
+        Assert.AreEqual(4, typeof(TestModel).GetField(nameof(TestModel.name))!.GetCustomAttributes().Count(a => a.GetType().FullName!.Contains("CommunityToolkit.Mvvm")));
         Assert.AreEqual(1, typeof(TestModel).GetMethod(nameof(TestModel.Test))!.GetCustomAttributes().Count(a => a.GetType().FullName!.Contains("CommunityToolkit.Mvvm")));
     }
 
@@ -33,6 +33,7 @@ public class TestModel
         [ObservableProperty]
         [AlsoNotifyChangeFor("")]
         [AlsoNotifyCanExecuteFor("")]
+        [AlsoBroadcastChange]
         public string? name;
 
         [ICommand]