Unhelpful error message when invalid resource key

Describe the bug Was trying to launch my application and getting a Error HRESULT E_FAIL has been returned from a call to a COM component. message on start with no additional information or stacktrace as to what the problem was.

Turned out, I had a StaticResource key referencing something that didn’t exist by mistake. It’d be great if VS could point this out ahead of time or the runtime error message be more useful here for debugging.

E.g.

<Style x:Key="TokenizingTextBoxItemTokenStyle" TargetType="controls:TokenizingTextBoxItem">
...
</Style>

<Style TargetType="controls:TokenizingTextBoxItem" BasedOn="{StaticResource TokenizingTextBoxItemStyle}"/>

See the mismatch above in the Key to StaticResource lookup.

Expected behavior Error message calling out no resource found with given key would at least be a pointer.

Error Details

System.Runtime.InteropServices.COMException
  HResult=0x80004005
  Message=Error HRESULT E_FAIL has been returned from a call to a COM component.
  Source=<Cannot evaluate the exception source>
  StackTrace:
<Cannot evaluate the exception stack trace>

Version Info

Windows 10 version	Saw the problem?
Insider Build (19615)	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 Thought I had maybe filed a similar bug before, but couldn’t find it?

[michael-hawker]

Hit another case where I just got a unhelpful:

Error HRESULT E_FAIL has been returned from a call to a COM component.

Coming from the ResourceDictionary type itself.

It was a case where I was trying to assign the wrong type of resource to another resource…

    <ResourceDictionary>
        <SolidColorBrush x:Key="ButtonForegroundPointerOver" Color="{StaticResource RainbowBrush}" />

RainbowBrush in this case was a LinearGradientBrush, so loading this ResourceDictionary was failing at runtime, no indication that this was a problem or pointing me in the right direction… ☹

[fabiant3]

Is this managed or C++? There should be stowed exceptions with more info (you might need to turn on mixed debugging). As for the original issue I had a resource that it did not really exist, we had planned to make changes to our compiler pipeline to detect these cases and give you a compile time error (similar for Binding and other related misfires).
Unfortunately this will only happen post WinUI 3.0, currently we’re shooting for tooling parity.