Update '[ObservableProperty]' attribute

src/CommunityToolkit.Mvvm/ComponentModel/Attributes/ObservablePropertyAttribute.cs

@@ -8,7 +8,7 @@
 namespace CommunityToolkit.Mvvm.ComponentModel;
 
 /// <summary>
-/// An attribute that indicates that a given field should be wrapped by a generated observable property.
+/// An attribute that indicates that a given partial property should be implemented by the source generator.
 /// In order to use this attribute, the containing type has to inherit from <see cref="ObservableObject"/>, or it
 /// must be using <see cref="ObservableObjectAttribute"/> or <see cref="INotifyPropertyChangedAttribute"/>.
 /// If the containing type also implements the <see cref="INotifyPropertyChanging"/> (that is, if it either inherits from
@@ -20,38 +20,54 @@ namespace CommunityToolkit.Mvvm.ComponentModel;
 /// partial class MyViewModel : ObservableObject
 /// {
 ///     [ObservableProperty]
-///     private string name;
+///     public partial string name { get; set; }
 ///
 ///     [ObservableProperty]
-///     private bool isEnabled;
+///     public partial bool IsEnabled { get; set; }
 /// }
 /// </code>
 /// </para>
 /// And with this, code analogous to this will be generated:
 /// <code>
 /// partial class MyViewModel
 /// {
-///     public string Name
+///     public partial string Name
 ///     {
-///         get => name;
-///         set => SetProperty(ref name, value);
+///         get => field;
+///         set => SetProperty(ref field, value);
 ///     }
 ///
-///     public bool IsEnabled
+///     public partial bool IsEnabled
 ///     {
-///         get => isEnabled;
-///         set => SetProperty(ref isEnabled, value);
+///         get => field;
+///         set => SetProperty(ref field, value);
 ///     }
 /// }
 /// </code>
 /// </summary>
 /// <remarks>
+/// <para>
+/// In order to use this attribute on partial properties, the .NET 9 SDK is required, and C# preview must
+/// be used. If that is not available, this attribute can be used to annotate fields instead, like so:
+/// <code>
+/// partial class MyViewModel : ObservableObject
+/// {
+///     [ObservableProperty]
+///     private string name;
+///
+///     [ObservableProperty]
+///     private bool isEnabled;
+/// }
+/// </code>
+/// </para>
+/// <para>
 /// The generated properties will automatically use the <c>UpperCamelCase</c> format for their names,
 /// which will be derived from the field names. The generator can also recognize fields using either
 /// the <c>_lowerCamel</c> or <c>m_lowerCamel</c> naming scheme. Otherwise, the first character in the
 /// source field name will be converted to uppercase (eg. <c>isEnabled</c> to <c>IsEnabled</c>).
+/// </para>
 /// </remarks>
-[AttributeUsage(AttributeTargets.Field, AllowMultiple = false, Inherited = false)]
+[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
 public sealed class ObservablePropertyAttribute : Attribute
 {
 }