XamlCompilation does not work on Debug

[busec0]

Description

XamlCompilation does not work on Debug configuration.

Similar with: #3794. It looks like this is a known thing/issue.

Any workaround for this? Is this intended to work only for Release targets? If yes, why?

Note: XamlCompilation works on Debug as well on Xamarin apps.

Steps to Reproduce

1. On a maui sample app, add:

[assembly: XamlCompilation(XamlCompilationOptions.Compile)]

2. Inspect the generated IL.
3. Notice that on a debug configuration, the XamlCompilationOptions.Compile setting has no effect.

Version with bug

6.0.400 (current)

Last version that worked well

Unknown/Other

Affected platforms

iOS, Android, I was not able test on other platforms

Affected platform versions

Latest

Did you find any workaround?

No.

Relevant log output

No response

[StephaneDelcroix]

As XamlC (XAML Compilation) is a perf enhancement, but comes at a compilation cost, we made some tradeoff vs what we were doing on Xamarin.Forms:

• XAMLC is executed on DEBUG, so you get the compilation errors, but the generated IL isn't written to the assembly, and saves a lot of time in the developer loop (code-build-run)
• For runtime builds, we enable XAMLC, and IL writing, for perf reasons

The msbuild variable to change this behaviour isn't considered public API (starts with an _), so I won't advertise it, but it can be found on this line: https://github.com/dotnet/maui/blob/main/.nuspec/Microsoft.Maui.Controls.targets#L146