.NET10-rc1 The type or namespace name 'XamlProcessingAttribute' could not be found

[bcaceiro]

Description

After upgrading to RC1 - now it's not possible to try out the Xaml source gen:

Adding this: [assembly: XamlProcessing(XamlInflator.SourceGen)] - from the docs https://learn.microsoft.com/en-us/dotnet/maui/whats-new/dotnet-10?view=net-maui-9.0#xaml

On the top of the app.xaml.cs

[assembly: XamlProcessing(XamlInflator.SourceGen)]
namespace Maui10Preview7
{
    public partial class App : Application
    {
        public App()
        {
            InitializeComponent();
        }

        protected override Window CreateWindow(IActivationState? activationState)
        {
            return new Window(new AppShell());
        }
    }
}

'XamlInflator' is inaccessible due to its protection level
The type or namespace name 'XamlProcessing' could not be found (are you missing a using directive or an assembly reference?)
The type or namespace name 'XamlProcessingAttribute' could not be found (are you missing a using directive or an assembly reference?)

Also I am using visual Studio insiders , and my workloads are:

Workload version: 10.0.100-manifests.a6e8bec0

Installed Workload Id      Manifest Version                         Installation Source
---------------------------------------------------------------------------------------------------------------------------
android                    36.0.0-rc.1.285/10.0.100-rc.1            VS 17.14.36429.23, VS 17.14.36429.23, VS 18.0.11005.162
ios                        18.5.10727-net10-rc.1/10.0.100-rc.1      VS 17.14.36429.23, VS 17.14.36429.23, VS 18.0.11005.162
maccatalyst                18.5.10727-net10-rc.1/10.0.100-rc.1      VS 17.14.36429.23, VS 17.14.36429.23, VS 18.0.11005.162
maui-windows               10.0.0-rc.1.25452.6/10.0.100-rc.1        VS 17.14.36429.23, VS 17.14.36429.23, VS 18.0.11005.162

Steps to Reproduce

1. Create a new .net maui app with rc1

2. add [assembly: XamlProcessing(XamlInflator.SourceGen)]

3. Build -> see error

Link to public reproduction project repository

https://github.com/bcaceiro/net9-repros/tree/main/Maui10Preview7

Version with bug

10.0.0-rc.1

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

10.0.0-preview.7

Affected platforms

Android

Affected platform versions

No response

Did you find any workaround?

Just disabling the feature

Relevant log output

1>------ Build started: Project: Maui10Preview7, Configuration: Debug Any CPU ------
1>C:\Program Files\dotnet\sdk\10.0.100-rc.1.25451.107\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.RuntimeIdentifierInference.targets(345,5): message NETSDK1057: You are using a preview version of .NET. See: https://aka.ms/dotnet-support-policy
1>Skipping analyzers to speed up the build. You can execute 'Build' or 'Rebuild' command to run analyzers.
1>Including assemblies for Hot Reload support
1>C:\P\net9-repros\Maui10Preview7\App.xaml.cs(1,12,1,26): error CS0246: The type or namespace name 'XamlProcessingAttribute' could not be found (are you missing a using directive or an assembly reference?)
1>C:\P\net9-repros\Maui10Preview7\App.xaml.cs(1,12,1,26): error CS0246: The type or namespace name 'XamlProcessing' could not be found (are you missing a using directive or an assembly reference?)
1>C:\P\net9-repros\Maui10Preview7\App.xaml.cs(1,27,1,39): error CS0122: 'XamlInflator' is inaccessible due to its protection level
1>Done building project "Maui10Preview7.csproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
========== Build completed at 08:43 and took 03,991 seconds ==========
========== Deploy: 0 succeeded, 0 failed, 0 skipped ==========
========== Deploy completed at 08:43 and took 03,991 seconds ==========

[bcaceiro]

@jfversluis Sorry to ping, however - the bug template is again not updated - I want to select RC1

[jfversluis]

@bcaceiro added, thanks!

[StephaneDelcroix]

We introduced [XamlProcessing] in -p7, and removed it in -rc1. It was still a preview feature.

The correct way to enable sourcegen for xaml inflation is by using msbuild metadata in you .csproj

<ItemGroup>
    <MauiXaml Update="MyPage.xaml" Inflator="SourceGen" />
</ItemGroup>

or you can wildcard it

<ItemGroup>
    <MauiXaml Update="**\*.xaml" Inflator="SourceGen" />
</ItemGroup>

We're very pleased that you're trying this preview feature, hope you'll find some enhancement in -rc1, and we can't wait to deliver -rc2 in which sourcegen inflation should be on par with runtime and XamlC inflators you were using in the past.

Make sure to report any issue found

[bcaceiro]

We introduced [XamlProcessing] in -p7, and removed it in -rc1. It was still a preview feature.

The correct way to enable sourcegen for xaml inflation is by using msbuild metadata in you .csproj

or you can wildcard it We're very pleased that you're trying this preview feature, hope you'll find some enhancement in -rc1, and we can't wait to deliver -rc2 in which sourcegen inflation should be on par with runtime and XamlC inflators you were using in the past.

Make sure to report any issue found

Thank you for the clarification, I would suggest to update also the documentation

Also, since I have multiple projects in my solution, I'm guessing this has to be applied in all of them. In the future, will it be simplier like a flag to apply to all of the solution automatically?

[StephaneDelcroix]

I would suggest to update also the documentation

the documentation refer to p7, so it's still accurate. we will make sure it's updated when the doc for -rc1 is out

I have multiple projects in my solution, I'm guessing this has to be applied in all of them

this is still a preview feature. If it works for you, use it, but we can't guarantee it'll work in all situations. At some point, we'll make it the default.

you want to enable it for all your solutions ? do it in a Directory.build.props file at the root of your solution

[StephaneDelcroix]

and I forgot, there's also a MauiXamlInflator property you can set for your project, if the metadata update syntax is too opaque

accepted values are either "SourceGen", "XamlC", "Runtime", but leave it unset for anything but SourceGen (if you set it to Runtime, you're release perks will be abysmal, and if you set it to XamlC, it might hurt your debug experience and build times)

[bcaceiro]

and I forgot, there's also a MauiXamlInflator property you can set for your project, if the metadata update syntax is too opaque

accepted values are either "SourceGen", "XamlC", "Runtime", but leave it unset for anything but SourceGen (if you set it to Runtime, you're release perks will be abysmal, and if you set it to XamlC, it might hurt your debug experience and build times)

I am sorry, you lost me here - how can I set the MauiXamlInflator for the project then?

[StephaneDelcroix]

I am sorry, you lost me here - how can I set the MauiXamlInflator for the project then?

<PropertyGroup>
   <MauiXamlInflator>SourceGen</MauiXamlInflator>
</PropertyGroup>

[bcaceiro]

I am sorry, you lost me here - how can I set the MauiXamlInflator for the project then?

SourceGen

Thank you, it worked!

@StephaneDelcroix should I create new bug reports based on this, or since it is just experimental no point in doing so?
I am getting build errors with ResourceDictionary files , or a Colors.xml files

[StephaneDelcroix]

@bcaceiro file the issues, even if a lot of fixes are coming in -rc2

[MartyIX]

@StephaneDelcroix It appears that the XAML inflator in .NET MAUI 10-RC1 does not support:

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyMauiApp.MainPage"
             x:ClassModifier="Internal"> <!-- NOTE: Internal is used here -->
    ...
</ContentPage>

(The sample is from docu https://learn.microsoft.com/en-us/dotnet/maui/xaml/class-modifiers?view=net-maui-9.0)

Is it a known issue perhaps?