DataTemplateView - System.Linq.Expressions vs. linker trimming and NativeAOT

[Numpsy]

A question about DataTemplateView and TreeViews, related to an issue I've seen before with linker trimming, and think I hit again in the diagnostic tools when looking at #399:

In DataTemplateView, we have:

Avalonia.FuncUI/src/Avalonia.FuncUI/DataTemplateView.fs

Line 16 in 1d562ee

itemsSource: Expression<Func<'data, 'childData seq>> voption,

Which is using System.Linq.Expressions, which are compiled at

Avalonia.FuncUI/src/Avalonia.FuncUI/DataTemplateView.fs

Line 42 in 1d562ee

InstancedBinding.OneTime(expression.Compile().Invoke(data))

When testing with single-file / trimmed builds of code using a TreeView with that code path, I've seen runtime errors occur because it seems that code inside of delgates passed to itemsSelector gets trimmed out, even though it's used.
When I was just testing with the ContactBook address app, I hit this crash when navigating around the diagnostics tools

S:\GitHubForks\MyFuncUI\src\Examples\Component Examples\Examples.ContactBook\bin\Release\net6.0\publish>Examples.ContactBook.exe
Unhandled Exception: System.InvalidOperationException: Could not bind function OfList in type Microsoft.FSharp.Collections.SeqModule
   at Microsoft.FSharp.Quotations.PatternsModule.u_ModuleDefn$cont@2029(FSharpOption`1, Type, String, Unit) + 0x2b4
   at Microsoft.FSharp.Quotations.PatternsModule.u_constSpec(PatternsModule.SimpleUnpickle.InputState) + 0x2d
   at Microsoft.FSharp.Quotations.PatternsModule.u_Expr(PatternsModule.SimpleUnpickle.InputState) + 0x41
   at Microsoft.FSharp.Quotations.PatternsModule.u_Expr(PatternsModule.SimpleUnpickle.InputState) + 0x186
   at Microsoft.FSharp.Quotations.PatternsModule.SimpleUnpickle.u_list_aux[a](FSharpFunc`2, FSharpList`1, PatternsModule.SimpleUnpickle.InputState) + 0x55
   at Microsoft.FSharp.Quotations.PatternsModule.u_Expr(PatternsModule.SimpleUnpickle.InputState) + 0xfa
   at Microsoft.FSharp.Quotations.PatternsModule.u_Expr(PatternsModule.SimpleUnpickle.InputState) + 0x228
   at Microsoft.FSharp.Quotations.PatternsModule.deserialize(Type, Type[], Type[], FSharpExpr[], Byte[]) + 0xce
   at <StartupCode$Avalonia-FuncUI-Diagnostics>[email protected](IComponentContext) + 0x1a4
   at Avalonia.FuncUI.ComponentBase.UIThreadUpdate() + 0x2d

Which looks like it's the same issue, from

Avalonia.FuncUI/src/Avalonia.FuncUI.Diagnostics/Views/Views.StateHookViews.fs

Line 85 in 1d562ee

(fun info -> Seq.ofList info.Source.InstanceType.Sources),

I'm not sure what's going on behind the scenes here (it looks like F# compiler is doing complicated things in the background when binding a Lambda into a Linq.Expression), and there are various ways to prevent the code being trimmed out, but however - i'm not particularly clear on the reason for using Expression for itemsSource here, so I'm not sure uf there's a simpler way to avoid the issues?

[JaggerJo]

Feel free to change it!

Don't think there was a particular reason for it.

[Numpsy]

If I change itemsSource from

Expression<Func<'data, 'childData seq>> voption

to just

Func<'data, 'childData seq> voption

Then the solution still builds and the diagnostic tools in the contact book no longer fall over with the exception in the description, though that would be a breaking API change (maybe you could alleviate some breakages there with more overloads of DataTemplateView.Create if needed though).

Looking at the Avalonia code, using Func<> directly looks closer to how FuncTreeDataTemplate works.

[JaggerJo]

Might be breaking, but easy to fix.