🧪 [Experiment] DependencyPropertyGenerator

[Sergio0694]

Note

Originally from #449.

Overview

Tracking issue for the new DependencyProperty generator, for UWP (both .NET Native and .NET 9) and WinUI 3.
This is what using the new generator looks like:

[GeneratedDependencyProperty]
public string? Name { get; set; }

It only supports instance properties. Attached properties are not currently supported.

Remaining task

Here's a few remaining tasks to track work:

• Codegen for DefaultValueCallback
• Improve formatting for PropertyMetadata construction
• Diagnostic for using DefaultValue and DefaultValueCallback at the same time
• Diagnostic for DefaultValueCallback set to null
• Diagnostic for DefaultValueCallback not matching an existing method
• Diagnostic for DefaultValueCallback matching an invalid method (eg. wrong signature)
• Diagnostic for properties that end with the "Property" suffix
• Handle generic containing types
• Handle default(T) for default values on unconstrained generic type parameters
• Diagnostics for [NotNull] on property getters

[insomniachi]

Why was the name of the attribute changed from DependencyPropertyAttribute to GeneratedDepedencyPropertyAttribute?
it causes some conflict with existing DependencyProperty class?
we don't have the word Generated in ObservablePropertyAttribute

[michael-hawker]

@insomniachi see the comment here: #617 (comment)

In theory we could name it the same, it wouldn't conflict because it's an attribute. But in general, the convention is to use the "Generated" prefix for attributes triggering generation (eg. see [GeneratedComInterface], GeneratedComClass], [GeneratedRegex], etc.). If anything, it's the attributes in the MVVM Toolkit that are kinda breaking this 😅

[michael-hawker]

@Arlodotexe should we re-open this for tracking or have another tracking issue? It got closed from the first PR merging.

[Arlodotexe]

@Arlodotexe should we re-open this for tracking or have another tracking issue? It got closed from the first PR merging.

@michael-hawker Since this is a brand-new component and not a porting checklist, I think it makes sense to keep this ticket around for tracking the component. Sub-issues shouldn't close it in the future.

[Poker-sang]

Nice experience. But how can I suppress the null warning (without #pragma)?

How about suppress WCRTDPG0009 when the DefaultValue is null!?(This means we suppress it manually)

[Poker-sang]

and it does not show xml doc:

[Poker-sang]

Looks like it doesn't take covariation into account?

[michael-hawker]

Just wanted to link to open PR around getting better documentation here: #665

[michael-hawker]

@Sergio0694 for attached properties, was this not our best hope for simplification?

    [GeneratedAttachedProperty]
    public static partial int GetMyValue(DependencyObject obj);

As we still have the property value type (int), the property name (after Get), and the target attachment type (parameter type).

It's not the prettiest or simplest to remember, but this is the rarest of properties to use. The setter is just more verbose, and we can't really use the field masquerading as a property as we can't generate that, right?

And for existing implementations, this'll still exist, so a fixer would just remove the body and mark it partial + attribute, and then have to remove the other bits.