Error out properly when building WPF on ARM64 app until support is added.

In #7457 we added support for WinForms apps targeting Windows ARM64, but not WPF. A RID specific build/publish fails appropriately if UsingWpf is set (it claims that the WPF pack is not a valid framework reference). However, a RID agnostic WPF app successfully builds (be it on the ARM64 device itself or on a crossbuild), but will fail at runtime on ARM64. The shared framework on ARM64 doesn’t have the WPF bits and will end up throwing a FileNotFound exception.

[hoyosjs]

This issue was opened per my recommendation, which is this: Even if this is only a temporary situation, make it an error to attempt publishing UseWpf=true when RID=win-arm64.

This fails properly as you said with UseWpf: dotnet publish -r -win-arm64 This doesn’t: dotnet publish on arm64 or cross compile and marshal bits

[dsplaisted]

I’m not sure we should do anything in the SDK for this. There can be a difference between the architecture you are building on and the one that you will run on. You could build a runtime dependent WPF app on an x64 machine, and it would work on that machine but fail to run on an ARM machine. You could build the same app on an ARM machine, and the output should be the same- ie it would fail to run on the ARM machine but would run if you copied it over to an x64 machine.

We could add a warning when building a WPF app on an ARM64 machine, but if we’re eventually going to support WPF on ARM64 anyway, it may be OK to just leave the current behavior.