Namespace collision when used with WinUI 3

[wjk]

When you link WinUI 3 into your app, it defines a namespace called Microsoft.System. CsWin32 outputs go into Microsoft.Windows.Sdk. Notice the common prefix. The generated code (ab)uses a strange quirk of the C# language by placing its using statements inside the namespace body, which changes the algorithm used to look up types. This results in using System.Runtime.InteropServices resolving to the namespace Microsoft.System.Runtime.InteropServices because of the common prefix. Of course, this namespace doesn’t exist, which breaks the build. Hence, CsWin32 and WinUI 3 cannot coexist in the same project.

The fix here is dead simple: Move the using statements to the top of the file, outside the namespace, which is where they should have been in the first place. When you do this, the using statements will be resolved exactly as they are specified. Thanks!

[AArnott]

The fix here is dead simple: Move the using statements to the top of the file, outside the namespace, which is where they should have been in the first place.

That's one option. There are actually using directives that only work when inside the namespace, just FYI. That isn't the case here, but we already avoid this problem using the global:: prefix on our using directives.

What version of CsWin32 are you using that has this bug? It doesn't repro on 0.1.422-beta, I think.

[AArnott]

See #124 for the original report and fix for the namespace collision.

[wjk]

You are correct. This has been fixed since I last used CsWin32 and WinUI 3 together. Thank you for your assistance.

[dotMorten]

Still seeing this issue. Repro steps:
1 Install Project Reunion Project Templates: https://marketplace.visualstudio.com/items?itemName=ProjectReunion.MicrosoftProjectReunion
2. Create a new Blank App, Packaged (WinUI 3 in Desktop) project.
3. Add CsWin32 nuget v0.1.422-beta
4. Add NativeMethods.txt and some interop methods to it.
5. Open MainWindow.xaml.cs, and in the constructor add a pinvoke method call.
6. Compile
7. Observe errors

Seems to happen when there's an XAML file in the project. Doesn't happen if there's no xaml in the project.

Repro sample:
App39.zip

Using VS16.10.p1

/cc @AArnott

[AArnott]

@dotMorten, can you navigate to the generated file and line that produces the error and copy the code snippet into the issue?

[dotMorten]

@AArnott Here: Doesn't show any squiggles, so think it is still the xaml precompile step causing it

I figured changing the default namespace would fix the problem, but that doesn't help, so it isn't a namespace collision.

[AArnott]

oh, it's complaining about your code, @dotMorten ? I don't know there's anything we can do about that. Try adding global:: in front of your fully-qualified types on that line.

[dotMorten]

@AArnott Well it's complaining about calling "your" code :-) It's not a namespace collision issue (see last line in my above comment).
I think the xaml precompile step compiles this code prior to the generated code getting included.

[AArnott]

Ok, so this looks like a project reunion flavor of #7, but the WPF workaround is apparently not effective in Reunion. I filed https://github.com/dotnet/roslyn/issues/52306 to get this fixed.

[AArnott]

This isn't a namespace collision with WinUI which is what this bug was tracking, so I'm going to re-close this issue. We'll open another issue in this repo to track the dotnet/roslyn one.