Is it possible to detect Xaml root element type and idl type mismatch?

[HO-COOH]

Describe the bug

I am creating a ResourceDictionary with code-behind to be able to use x:Bind, so I created it with the UserControl file template, change the xaml root element to ResourceDictionary, then I build the project, and it builds.

Later I realized, I forgot to also change the idl type to ResourceDictionary.

My question is is there any possibility to detect such type mismatch?

Why is this important?

Saves time. Because editing one single idl file will require the whole project rebuild, which is exremely time-consuming for C++ project.

Steps to reproduce the bug

As described above

Actual behavior

No response

Expected behavior

No response

Screenshots

No response

NuGet package version

WinUI 3 - Windows App SDK 1.7.3: 1.7.250606001

Windows version

Windows 11 (24H2): Build 26100

Additional context

No response

[DarranRowe]

While I can't comment on whether or not this can be done, the Xaml compiler does have all of the information.

The .idl files are used to generate the metadata (.winmd) file. This file is passed into the Xaml compiler as part of phase 2. So the Xaml compiler does see the application metadata file and the Xaml file.

[snigdha011997]

Hi @HO-COOH , can we have more descriptive information about the issue, like steps to understand it?

[DarranRowe]

@snigdha011997

My understanding is the following.

//TestControl.idl
namespace AppComponents
{
    [default_interface]
    runtimeclass TestControl : Microsoft.UI.Xaml.ResourceDictionary
    {
        TestControl();
        Int32 MyProperty;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<!--TestControl.xaml-->
<!--TestControl does not "derive" from UserControl-->
<UserControl
    x:Class="AppComponents.TestControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:AppComponents"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Grid>

    </Grid>
</UserControl>

This will not cause the Xaml compiler to emit an error. In fact, the build succeeds.

[HO-COOH]

@DarranRowe Yes, this is largely what I meant.

I was doing this

<ResourceDictionary
    x:Class="AppComponents.TestControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:AppComponents"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">
    
    ......I was doing x:Bind in template so I need code-behind......
</ResourceDictionary>

namespace AppComponents
{
    [default_interface]
    runtimeclass TestControl : Microsoft.UI.Xaml.UserControl //Forget to change here
    {
        TestControl();
        Int32 MyProperty;
    }
}