WPF XAML file can't see types generated by Razor Source Generator

[Eilon]

• .NET Core Version: 6.0-preview3
• Windows version: N/A
• Does the bug reproduce also in WPF for .NET Framework 4.8?: N/A
• Is this bug related specifically to tooling in Visual Studio? No (interestingly, this does work in VS IntelliSense, but not when compiling!)

Problem description:

In .NET 6 we are enabling authoring of WPF apps in a "Blazor Desktop" scenario where Blazor web UI (HTML+CSS) is hosted in a web view in a WPF app. Such projects contain a mix of XAML (WPF), Blazor/Razor (HTML+CSS), and other code artifacts (C#, etc.). This is done with a new <BlazorWebView ... /> WPF control being built by the ASP.NET team.

The XAML compiler, however, is unable to see the types generated by the Razor Source Generator. (Note: Using a source generator is new for Blazor in .NET 6; previously it was done in other ways).

For the WPF BlazorWebView control we’d like to support a XAML syntax like this to specify a Razor component to load:

<Window ...
        xmlns:local="clr-namespace:BlazorWpfApp">
   <DockPanel>
        ...
        <blazor:BlazorWebView HostPage="wwwroot\index.html" Services="{StaticResource services}">
            <blazor:BlazorWebView.RootComponents>
                <blazor:RootComponent Selector="#app" ComponentType="{x:Type local:Main}" />
            </blazor:BlazorWebView.RootComponents>
        </blazor:BlazorWebView>
    </DockPanel>
</Window>

Where local:Main is a class that is generated by the Razor compiler as part of the project’s compilation. There is a file Main.razor that generates a type Main in the same namespace. The Razor-generated class is visible from C# code, but the XAML compiler is unable to find.

From @captainsafia in an email thread:

We'll need to do some work on the WPF size to react to the changes made in the Razor SDK.

Actual behavior:

In VS Intellisense you can see the Razor-generated types (good):

But when you try to compile the app, the XAML compiler can't see the same type anymore (bad):

...\MainWindow.xaml(17,55): error MC3050: Cannot find the type 'local:Main'. Note that type names are case sensitive. Line 17 Position 55.

Expected behavior:

The XAML compiler should be able to see the Razor generated types and compile.

Minimal repro:

See repro app here: https://github.com/Eilon/WPFXamlRazorGeneratorBug

To see just the relevant code, look at this commit: Eilon/WPFXamlRazorGeneratorBug@b500285

1. Open the SLN in VS
2. Try to run the app, you get the above-mentioned XAML compiler error
3. In MainWindow.xaml.cs un-comment the line at the bottom of the file
4. Then everything works fine

Workarounds:

There are workarounds for this issue:

1. In the WPF app create a partial class with the same name as the Razor-generated type. The types in Razor are all partial too, so this doesn't really create a new type, but it enables the XAML compiler to believe the type it exists, while creating no ill effects. For example partial class Index {}.
2. Move all the Razor files (*.razor) to a Razor Class Library so that all the Razor-generated types are available prior to the XAML compiler running, thus enabling it to "see" all the types.

cc @captainsafia @danroth27

[captainsafia]

Some more helpful info from the email thread:

It looks like you might be running into some issues related to a breaking change that we made recently in the Razor compiler (see aspnet/Announcements#459).

Previously, the Razor compiler produced a separate AppName.Views.dll assembly that contained the compiled view types in an application as public​ classes under the AspNetCore​namespace.

Now, the Razor compiler produces a single AppName.dll that contains the compiled view types as internal sealed​ classes under the AspNetCoreGenerated​ namespace.

My hunch is that this change is causing the problem that you see here. It's likely that your implementation will work in .NET 6 Preview 2 and earlier.

Our current model of compiling the views into a single assembly as internal​ types is in place to support some build improvements and hot reload so we'll need to sort out a solution for this moving forward.

[taoyouh]

Actually WPF XAML cannot see types generated by other "source generators" too. For example, the resource designer classes generated by VocaDb.ResXFileCodeGenerator cannot be used in WPF XAML file.

[ThomasGoulet73]

I opened #6535 which should fix the issue.

A temporary workaround would be to add <RootNamespace>WpfBlazorRepro</RootNamespace> to the csproj.