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Possibly wrong pattern match in VirtualizingStackPanel.GetControl #15955

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jnyrup opened this issue Jun 8, 2024 · 3 comments · Fixed by #16005
Closed

Possibly wrong pattern match in VirtualizingStackPanel.GetControl #15955

jnyrup opened this issue Jun 8, 2024 · 3 comments · Fixed by #16005
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bug help-wanted A contribution from the community would be most welcome.

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@jnyrup
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jnyrup commented Jun 8, 2024

Describe the bug

In C# the pattern x is not A or B is interpreted as x is (not A) or B and not x is not (A or B).

I was grep'ing my local git repositories for code that matched and stumbled upon

fromControl is null && direction is not NavigationDirection.First or NavigationDirection.Last)

So this code is not checking whether direction is "neither First nor Last".
As Last is covered by not First Roslyn even lowers this to != First.
As such this looks like a bug to me

image

SharpLab

To Reproduce

I found this by analyzing the code and didn't write any code I don't know and haven't looked into if this potential bug can be hit.

Expected behavior

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Avalonia version

master

OS

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Additional context

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@jnyrup jnyrup added the bug label Jun 8, 2024
@maxkatz6
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It is wrong, you are correct.
Whole condition should be changed from

if (count == 0 || 
-                fromControl is null && direction is not NavigationDirection.First or NavigationDirection.Last)
+               (fromControl is null && direction != NavigationDirection.First && direction != NavigationDirection.Last)

@maxkatz6 maxkatz6 added the help-wanted A contribution from the community would be most welcome. label Jun 11, 2024
@timunie
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timunie commented Jun 11, 2024

@jnyrup maybe you can file a PR with the fix? 🙏 thx

@jnyrup
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jnyrup commented Jun 11, 2024

@jnyrup maybe you can file a PR with the fix? 🙏 thx

Unfortunately I don't have the time to do this.
I'll pass it on to other contributors.

@nil4 nil4 mentioned this issue Jun 12, 2024
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github-merge-queue bot pushed a commit that referenced this issue Jun 14, 2024
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3 participants