'XamlBindings': undeclared identifier in C++/WinRT

[sylveon]

Describe the bug
I get the compiler error 'XamlBindings': undeclared identifier when using x:Bind in a ControlTemplate as part of a XAML document that isn't in the root namespace with C++/WinRT.

Steps to reproduce the bug

1. Create a new C++/WinRT UWP app (with minimum version 17763)
2. Create a page that isn't in the project's root namespace (ex BlankApp1.Foo.MyPage)
3. Within that page, retemplate a control and use x:Bind in the template, for example

   <Button x:Name="myButton" Click="ClickHandler">
       <Button.Template>
           <ControlTemplate TargetType="Button">
               <ContentPresenter Width="{x:Bind Width}" ></ContentPresenter>
           </ControlTemplate>
       </Button.Template>
       Click Me
   </Button>

4. Try building the project.
5. Observe a compiler error in Foo.MyPage.xaml.g.hpp

Expected behavior
It builds.

Version Info
Visual Studio 16.6.0 Preview 6.

NuGet package version:
C++/WinRT 2.0.200508.4

Windows 10 version	Saw the problem?
Insider Build (19041)	Yes
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Mobile
Xbox
Surface Hub
IoT

Additional context
Full output:

1>------ Build started: Project: BlankApp2, Configuration: Debug Win32 ------
1>App.cpp
1>Foo.MainPage.cpp
1>XamlTypeInfo.g.cpp
1>T:\Projects\BlankApp2\Generated Files\Foo.MainPage.xaml.g.hpp(81,55): error C2065: 'XamlBindings': undeclared identifier
1>T:\Projects\BlankApp2\Generated Files\Foo.MainPage.xaml.g.hpp(71): message : while compiling class template member function 'winrt::Windows::UI::Xaml::Markup::IComponentConnector winrt::BlankApp2::Foo::implementation::MainPageT<winrt::BlankApp2::Foo::implementation::MainPage>::GetBindingConnector(int32_t,const winrt::implements<D,winrt::BlankApp2::Foo::MainPage,winrt::composing,winrt::Windows::UI::Xaml::Controls::IPageOverrides,winrt::Windows::UI::Xaml::Controls::IControlOverrides,winrt::Windows::UI::Xaml::Controls::IControlOverrides6,winrt::Windows::UI::Xaml::IFrameworkElementOverrides,winrt::Windows::UI::Xaml::IFrameworkElementOverrides2,winrt::Windows::UI::Xaml::IUIElementOverrides,winrt::Windows::UI::Xaml::IUIElementOverrides7,winrt::Windows::UI::Xaml::IUIElementOverrides8,winrt::Windows::UI::Xaml::IUIElementOverrides9,winrt::Windows::UI::Xaml::Markup::IComponentConnector,winrt::Windows::UI::Xaml::Markup::IComponentConnector2>::IInspectable &)'
1>        with
1>        [
1>            D=winrt::BlankApp2::Foo::implementation::MainPage
1>        ]
1>T:\Projects\BlankApp2\Generated Files\winrt\Windows.UI.Xaml.Markup.h(361): message : see reference to function template instantiation 'winrt::Windows::UI::Xaml::Markup::IComponentConnector winrt::BlankApp2::Foo::implementation::MainPageT<winrt::BlankApp2::Foo::implementation::MainPage>::GetBindingConnector(int32_t,const winrt::implements<D,winrt::BlankApp2::Foo::MainPage,winrt::composing,winrt::Windows::UI::Xaml::Controls::IPageOverrides,winrt::Windows::UI::Xaml::Controls::IControlOverrides,winrt::Windows::UI::Xaml::Controls::IControlOverrides6,winrt::Windows::UI::Xaml::IFrameworkElementOverrides,winrt::Windows::UI::Xaml::IFrameworkElementOverrides2,winrt::Windows::UI::Xaml::IUIElementOverrides,winrt::Windows::UI::Xaml::IUIElementOverrides7,winrt::Windows::UI::Xaml::IUIElementOverrides8,winrt::Windows::UI::Xaml::IUIElementOverrides9,winrt::Windows::UI::Xaml::Markup::IComponentConnector,winrt::Windows::UI::Xaml::Markup::IComponentConnector2>::IInspectable &)' being compiled
1>        with
1>        [
1>            D=winrt::BlankApp2::Foo::implementation::MainPage
1>        ]
1>T:\Projects\BlankApp2\Foo.MainPage.h(8): message : see reference to class template instantiation 'winrt::BlankApp2::Foo::implementation::MainPageT<winrt::BlankApp2::Foo::implementation::MainPage>' being compiled
1>T:\Projects\BlankApp2\Generated Files\Foo.MainPage.xaml.g.hpp(81,45): error C2672: 'winrt::make_self': no matching overloaded function found
1>T:\Projects\BlankApp2\Generated Files\Foo.MainPage.xaml.g.hpp(88,1): error C2974: 'winrt::make_self': invalid template argument for 'D', type expected
1>T:\Projects\BlankApp2\Generated Files\winrt\base.h(7458): message : see declaration of 'winrt::make_self'
1>Done building project "BlankApp2.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

This also affects other use cases, like a control inheriting from another and retemplating the parent, binding some values to its own properties. (that was how I found it, because my controls are under the MyRootNamespace.Controls namespace)

I cannot use TemplateBinding because I would like to provide a TargetNullValue fallback, which is not possible with TemplateBinding.

You can find my use case here https://github.com/TranslucentTB/TranslucentTB/tree/develop. The issue can be reproduced simply by building the Xaml project which has no other dependencies than the community toolkit's XamlApplication, C++/WinRT and the VCTRForwarders.

Moved from microsoft/cppwinrt#614

[sylveon]

According to documentation linked below, x:Bind in control templates is supported since 17763: https://docs.microsoft.com/en-us/windows/uwp/xaml-platform/templatebinding-markup-extension#xbind-in-controltemplate

It indeed works fine when using C#, and the C++/WinRT code for it is generated as well, it's just a omission of a namespace qualifier for a make_self<> call in a part of the codegen that is causing trouble.

[stevenbrix]

According to documentation linked below, x:Bind in control templates is supported since 17763:

@sylveon yes it has! Glad that you were able to discover that :)

[sylveon]

I'm currently having to debug a runtime binding issue and the lack of x:Bind is being severely felt :(

Having a compile time error would be much easier to correct.

[sylveon]

repro.zip
Here's a minimum repro project

[roxk]

Could reproduce similar issue in WinUI3 as well. I have a PostsPage in root-namespace.Presentation.UI.Posts and when building the project the compiler complains it cannot find XamlBindingTrackBase.

Screenshot
Notice how XamlingBindingTrackBase lack namespace prefix, while ReferenceTypeXamlBindings below have it.

[stevenbrix]

@sylveon, gotcha, so this is just a simple bug in the C++/WinRT codegen, then?

[stevenbrix]

@RealTommyKlein can you take a look at this? This sounds like a simple fix we could make in the 3.0 timeframe?

[sylveon]

Yes, it's simply missing a namespace qualifier

[RealTommyKlein]

Yeah we can fix this for WinUI 3. I've fixed the XamlBindingTrackingBase issue locally, will also convert the original repro app to WinUI 3 and verify the XamlBindings issue is fixed too.

[sylveon]

Would love to see this backported to the system XAML compiler, since I use XAML Islands so I would have to wait for WinUI 3.1 to get the fix

[RealTommyKlein]

We'll also backport both fixes for Windows.UI.Xaml, but to set expectations for a timeline, it won't be available until the Windows SDK release in mid-2021 due to the Windows shipping schedule.

[sylveon]

Fixed in the Windows 11 SDK, thanks ♥