Is the compatibility namespace usable?

[bradencohen]

I deal in an area where I take a lot of XAML dynamically, and parse it on the fly (using LoadFromXaml). There have been hundreds of thousands of lines of XAML (for Xamarin) written this way.

I understand the caveats of having to move to a new framework, and definitely will encourage people to update their XAML, but I want to make the process as easy as possible. I thought the Microsoft.Maui.Controls.Compatibility namespace was my answer. I wanted to add a compatibility layer that when enabled, mapped the corresponding elements to their compatibility version, like such:

// Get compatibility elements
var asm = typeof( Microsoft.Maui.Controls.Compatibility.StackLayout ).Assembly;
var compatElements = asm.GetExportedTypes()
    .Where( t => t.Namespace == "Microsoft.Maui.Controls.Compatibility" )
    .Select( t => t.Name )
    .ToList();

Then when looping through the incoming XAML, process it like such.

public static void UpdateCompatibilityElementNamespaces( this XElement element )
{
    var currentXmlns = element.GetDefaultNamespace();
    var mauiCompatXmlns = XNamespace.Get( "clr-namespace:Microsoft.Maui.Controls.Compatibility;assembly=Microsoft.Maui.Controls" );

    if ( currentXmlns == mauiCompatXmlns )
    {
        return;
    }

    // I know I shouldn't do this in the loop, please don't yell at me.
    var asm = typeof( Microsoft.Maui.Controls.Compatibility.StackLayout ).Assembly;
    var compatElements = asm.GetExportedTypes()
        .Where( t => t.Namespace == "Microsoft.Maui.Controls.Compatibility" )
        .Select( t => t.Name )
        .ToList();

    // Loop through each element. Each one that has an applicable compatibility element should be prefixed with "compat:".
    foreach ( var descendant in element.DescendantsAndSelf().Where( e => e.Name.Namespace == currentXmlns && compatElements.Contains( e.Name.LocalName ) ) )
    {
        descendant.Name = mauiCompatXmlns.GetName( descendant.Name.LocalName );
    }
}

This method successfully maps all of the available elements to the "compat" namespace (Microsoft.Maui.Controls.Compatibility)....
But that's when things started going wrong. It seems like the compatibility elements.. barely work.

Without ANY of the parsing above, take the following XAML. Specifically the Grid:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:compat="clr-namespace:Microsoft.Maui.Controls.Compatibility;assembly=Microsoft.Maui.Controls">
    <ScrollView>
        <compat:StackLayout Spacing="16">
            <compat:Grid ColumnDefinitions="24, *"
                ColumnSpacing="16">
                <ContentView Grid.Column="0">
                    <Image Source="https://images.pexels.com/photos/850359/pexels-photo-850359.jpeg?cs=srgb&amp;dl=pexels-jess-bailey-designs-850359.jpg&amp;fm=jpg"
                        HeightRequest="24"
                        WidthRequest="24">
                    </Image>
                </ContentView>
                <Label Text="Pretty Flower" Grid.Column="1" />
            </compat:Grid>
        </compat:StackLayout>
    </ScrollView>
</ContentPage>

Displays something completely wrong:

When I remove the compat namespacing, everything looks normal.
That is just one issue I'm encountering, the other compat elements have some problems too (see #12415 (comment))

I guess there is just some unclarity:

1. Are the elements in that namespace supposed to be usable in the way I'm using them?
2. Can compatibility elements be used and mixed with normal ones?
3. Is this a hopeless path that I'm trekking down? Is there a better way to achieve the behavior I desire?

Thanks for taking the time to read this, any help or advice would be greatly appreciated.

[bradencohen]

I was able to strip this down even more, so it literally was just the Grid as a descendant of a ContentPage. I tested this on a fresh MAUI project.

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:compat="clr-namespace:Microsoft.Maui.Controls.Compatibility;assembly=Microsoft.Maui.Controls">
        <compat:Grid ColumnDefinitions="24, *" 
            ColumnSpacing="16">
            <ContentView Grid.Column="0">
                <Image Source="https://images.pexels.com/photos/850359/pexels-photo-850359.jpeg?cs=srgb&amp;dl=pexels-jess-bailey-designs-850359.jpg&amp;fm=jpg"
                    HeightRequest="24"
                    WidthRequest="24">
                </Image>
            </ContentView>
            <Label Text="Pretty Flower" Grid.Column="1" />
        </compat:Grid>
</ContentPage>

Which results in:

[bradencohen]

@hartez do you have any thoughts on this? Are the layouts in the compatibility namespace expected to behave like the Xamarin version?

It's completely fine if the answer is "don't use the compatibility layouts". I just don't want to spend time figuring out another solution if the compat namespace is supposed to be usable in the way I'm describing.

[bradencohen]

Filed a bug for this: #15454, so going to go ahead and close the discussion.