Raise a warning when platform-specific XAML namespace declaration has invalid URI

[MartinZikmund]

Current behavior

From Cheesebaron on X:

Trying to get SkiaSharp running on @unoplatform. Works fine in the Skia GTK project, but when running on Android or iOS, doesn't draw anything. The repro is below. Very simply added SkiaSharp and SkiaSharp.Views.Uno.WinUI to the shared project. Only when hot reload kicks in the Canvas is invalidated and draws. This happens on Mobile. With GTK, it seems to work and draws initially.

Expected behavior

No response

How to reproduce it (as minimally and precisely as possible)

https://github.com/Cheesebaron/UnoSkia

Workaround

No response

Works on UWP/WinUI

None

Environment

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NuGet package version(s)

No response

Affected platforms

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IDE

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IDE version

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Relevant plugins

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Anything else we need to know?

No response

[MartinZikmund]

Please also validate the behavior against WinUI implementation

[jeromelaban]

If this behavior is hot reload related, it's not fixed yet and may need to have 8.0.101 to work properly (it's still pending inhttps://github.com/unoplatform/uno.check/pull/223)

[ramezgerges]

The repro uses xmlns:skia="using:SkiaSharp.Views.Windows". The skia namespace is used by the XAML generator to make add platform-specific controls. Use any other name instead of skia to avoid this problem. Remaining to skia2 fixed the problem (thanks @Youssef1313 for noticing this).

[MartinZikmund]

@ramezgerges @Youssef1313 @jeromelaban I think it might make sense to detect this and warn the user:

1. Warn if any of our "default prefixes" is used with a different URI than what is defined in https://platform.uno/docs/articles/platform-specific-xaml.html#available-prefixes
2. Or warn specifically for the combination of "xmlns:skia" and "using:SkiaSharp.XYZ"

What do you think?

[Youssef1313]

@MartinZikmund That would be a duplicate of #14004 I think.

We could treat xmlns:any_platform="using:... as a CLR namespace instead of a conditional xmlns.

[Cheesebaron]

Thanks for looking into this! As you say, after changing the xmlns to something else, it works now.

[jeromelaban]

Raising a warning if the xmlns does not match the original name could be useful, indeed.

[ramezgerges]

@MartinZikmund should we close this in favour of #15064?

[MartinZikmund]

@ramezgerges this is a bit different than the other I think - this is to validate the URI matches, so it would apply even to prefixes like "android:" etc. The other is for usage of Skia and wasm secifically on non cross runtime libraries