[XSG][BindingSourceGen] Add support for CommunityToolkit.Mvvm ObservablePropertyAttribute

[Copilot]

Note

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It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Description of Change

Binding source generators now support properties generated by CommunityToolkit.Mvvm's [ObservableProperty] attribute. Previously, bindings failed because MAUI generators cannot see properties generated by other source generators.

Implementation (following PR #32954 pattern for RelayCommand):

• BindingSourceGen/ITypeSymbolExtensions.cs: Added TryGetObservablePropertyType() to detect fields with [ObservableProperty] and infer property types. Supports both camelCase and _camelCase field naming patterns.

• BindingSourceGen/PathParser.cs: Enhanced TryHandleSpecialCases() to handle ObservableProperty patterns as fallback when symbol resolution fails.

• BindingSourceGen/BindingSourceGenerator.cs: Updated GetLambdaReturnType() to infer types from ObservableProperty fields, enabling C# lambda bindings.

• SourceGen/ITypeSymbolExtensions.cs: Updated TryGetProperty() to check ObservableProperty-inferred properties, enabling XAML string-based bindings.

Works for both XAML and C# bindings:

public class MyViewModel
{
    [ObservableProperty]
    private string? name;  // Generates Name property
    
    [ObservableProperty]
    private ObservableCollection<Tag> _tags = new();  // Generates Tags property
}

<Label Text="{Binding Name}" />
<ListView ItemsSource="{Binding Tags}" />

label.SetBinding(Label.TextProperty, static (MyViewModel vm) => vm.Name);
listView.SetBinding(ListView.ItemsSourceProperty, static (MyViewModel vm) => vm.Tags);

Issues Fixed

Fixes #32597

Original prompt

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This section details on the original issue you should resolve

<issue_title>[XSG][BindingSourceGen] Add support for CommunityToolkit.Mvvm ObservablePropertyAttribute source generator</issue_title>
<issue_description>Similar to #32597
Related to #32953

The CommunityToolkit.Mvvm package contains a source generator which generates bindable property bolierplate code based on the [ObservableProperty] attribute: https://learn.microsoft.com/en-us/dotnet/communitytoolkit/mvvm/generators/observableproperty

Scenarios:

// applied to a field
[ObservableProperty]
private string? name;

// generated code:
/// <inheritdoc cref="_tags"/>
[global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", "8.3.0.0")]
[global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
public global::System.Collections.ObjectModel.ObservableCollection<global::TestSampleContentBindings.Models.Tag> Tags
{
    get => _tags;
    [global::System.Diagnostics.CodeAnalysis.MemberNotNull("_tags")]
    set
    {
        if (!global::System.Collections.Generic.EqualityComparer<global::System.Collections.ObjectModel.ObservableCollection<global::TestSampleContentBindings.Models.Tag>>.Default.Equals(_tags, value))
        {
            OnTagsChanging(value);
            OnTagsChanging(default, value);
            OnPropertyChanging(global::CommunityToolkit.Mvvm.ComponentModel.__Internals.__KnownINotifyPropertyChangingArgs.Tags);
            _tags = value;
            OnTagsChanged(value);
            OnTagsChanged(default, value);
            OnPropertyChanged(global::CommunityToolkit.Mvvm.ComponentModel.__Internals.__KnownINotifyPropertyChangedArgs.Tags);
        }
    }
}

Our source generators cannot see properties generated by other source generators, so the binding compilation will fail.

Our sample content template uses this source generator and we are currently failing over to reflection-based bindings.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [XSG][BindingSourceGen] Add support for CommunityToolkit.Mvvm ObservablePropertyAttribute source generator #32955

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[simonrozsival]

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