WPF: Adding xmlns with clr-namespace to XAML breaks build with cryptic error message

[BrunoJuchli]

Dear Oren
Today I tried converting a bare WPF Project, i.E. one that was created by VS 15.5.7 New -> Project -> WPF App (.Net Framework) to the new csproj sdk format. I got stuck with:

1>C:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\Microsoft.WinFx.targets(419,45): error MSB4057: The target "CoreCompile" does not exist in the project.

Removing the following line from MainWindow.xaml fixes the build:

xmlns:local="clr-namespace:SdkCsprojWpfSpike"

ATM I'm quite perplexed how this can have any effect on the build outcome, but I'd guess it's about the WPF two-pass build...?!

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Notably, (not) having the same line @ App.xaml doesn't matter.

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Sample Project

Using your sample project I can reproduce the same issue.
The steps I performed:

1 ./Samples/WpfApplication/MainWindow.xaml

insert the following as Line 8:

xmlns:local="clr-namespace:WpfApplication"

2 ./Samples/WpfApplication/WpfApplication.csproj

I've had to change the target framework to net471 - because I don't have net462 installed.

3 Open Csproj & Build

.. and you'll see

1>C:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\Microsoft.WinFx.targets(419,45): error MSB4057: The target "CoreCompile" does not exist in the project.

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I'd be happy providing a PR for the readme/wiki page to document this, at the least. Any directions for a header, where to place it the document?

[BrunoJuchli]

Also, adding a User Control (WPF) immediately breaks the build:

Same solution. Remove the xmlns:local:

[clairernovotny]

I haven't fully documented this yet as there are some nasty workarounds needed that will be going away soon-ish, I hope.

For now, NuGet Package Explorer is a good example to look at:
https://github.com/NuGetPackageExplorer/NuGetPackageExplorer/blob/master/PackageExplorer/NuGetPackageExplorer.csproj

Note the workarounds at the top and bottom of the file:
https://github.com/NuGetPackageExplorer/NuGetPackageExplorer/blob/master/PackageExplorer/NuGetPackageExplorer.csproj#L3-L7
https://github.com/NuGetPackageExplorer/NuGetPackageExplorer/blob/master/PackageExplorer/NuGetPackageExplorer.csproj#L39-L40

[BrunoJuchli]

@onovotny
Thanks for the quick answer.
That's a fix for the same issue (NuGet/Home#5894) that the sample project also contains a fix for, though it's slightly different.
I'll see what difference it makes and report back.

Also, out-of-the-box the NuGetPackageExplorer doesn't compile for me. Got a copy of the source code as zip, unpacked, and first was confronted with VS migration dialog + afterwards it didn't compile properly.
Can I ask what version of VS you are using?

Thanks!

[BrunoJuchli]

@onovotny
Thanks again - the lines you referenced in PackageExplorer did fix this issue.
In my case, the significant difference was made by

https://github.com/onovotny/MSBuildSdkExtras/blob/master/Samples/WpfApplication/WpfApplication.csproj#L7
vs
https://github.com/NuGetPackageExplorer/NuGetPackageExplorer/blob/master/PackageExplorer/NuGetPackageExplorer.csproj#L7

[clairernovotny]

I'm using VS 2017 15.5 for NuGet Package Explorer.

[glennawatson]

I was having the exactly same issue and replacing that line did the trick for me as well.