Incorrect warning about WindowsDesktop SDK

[clairernovotny]

I have a project that has some libraries/exe that use WPF and some that don't. The ones that do use the WindowsDesktop SDK. The ones that don't use the default SDK to prevent accidental WPF references.

I have a directory.build.props file that sets UseWPF to true so that I don't need them in all places.

In Preview 7, I now get this warning:

1>C:\Program Files\dotnet\sdk\3.0.100-preview7-012503\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.DefaultItems.targets(340,5): warning NETSDK1107: Microsoft.NET.Sdk.WindowsDesktop is required to build Windows desktop applications. 'UseWpf' and 'UseWindowsForms' are not supported by the current SDK.

That's coming from Microsoft.NET.Sdk.DefaultItems.targets. The check is being too aggressive.

[vatsan-madhavan]

/cc @nguerrera, @dsplaisted

Related: #3315

[vatsan-madhavan]

We have seen two kinds of problem reports:

i. Failing to change Microsoft.NET.Sdk to Microsoft.NET.Sdk.WindowsDesktop, setting UseWpf (or UseWindowsForms) to true, and attempting to build/port a WPF app (which, unsurprisingly, fails to build as expected)

ii. Using Microsoft.NET.Sdk.WindowsDesktop, but failing to set UseWpf or UseWindowsForms to true. Again, fails to build as expected.

We wanted to add suppressible warnings to help with both scenarios. This addresses the first one.

[clairernovotny]

@vatsan-madhavan the warning as it's defined does not appear to be suppressible https://github.com/dotnet/sdk/blob/master/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.DefaultItems.targets#L337-L342

[vatsan-madhavan]

<PropertyGroup> 
 <MSBuildWarningsAsMessages>$(MSBuildWarningsAsMessages);NETSDK1107</MSBuildWarningsAsMessages>
</PropertyGroup>

That should do it, I think.

[clairernovotny]

I'll give that a try. Any chance the check can determine if it's coming from a props/targets file and skip? Like if people are using props/targets, then they're an advanced user.

[dsplaisted]

No, there's not a way in MSBuild for a target to check where a property was set.

[vatsan-madhavan]

I'm open to ideas - @nguerrera / @dsplaisted , thoughts on how we may be able to improve this to have less friction?

We had a similar discussion about problems around multi-targeting when using WindowsDesktop SDK, where the discussion centered around the best implementation approach that would help those who need these sorts of warnings, vs. not creating friction for complex codebases.

[nguerrera]

I'm putting this in discussion milestone because this was a deliberate change. I think it's reasonable to put a suppression as shown above for the advanced cases.

[AArnott]

In my case I'm seeing the warning in a project the multi-targets. I only set UseWPF when targeting netcoreapp3.0 since of course that's the only TFM to which it applies. But I'm seeing the warning in other TFMs because the Sdk is of course not conditioned on the TFM.

[AArnott]

I'm using this to hide the warnings:

    <MSBuildWarningsAsMessages>$(MSBuildWarningsAsMessages);NETSDK1105</MSBuildWarningsAsMessages>
    <MSBuildWarningsAsMessages>$(MSBuildWarningsAsMessages);NETSDK1106</MSBuildWarningsAsMessages>

[sommmen]

NOTE as of now i use the following line to disable the warning:

<!-- Disable the warning useWpf gives. -->
<MSBuildWarningsAsMessages>$(MSBuildWarningsAsMessages);NETSDK1107</MSBuildWarningsAsMessages>

[marcpopMSFT]

@clairernovotny since WindowsDesktop is no longer required starting in 5.0-windows, can this issue be closed? I doubt we'd fix it for downlevel targeting at this point.