Fix delegation check on UDF for datasource type

[yuchenglin]

Probelm

UDF with direct assigned datasource type such as UDF1():Accounts = Accounts is always calculated as non-delegable.
There is no issue for UDF2():Accounts = Filter(Account, ...) since it would go through override validation in Filter class, where check data source metadata directly. UDF gets IsDelegatable from Top which is Filter().

Option 1 (current)

Handle in overridden IsServerDelegatable of UserDefinedFunction. It will go check data source metadata directly if it's FirstNameNode and haven't been processed.

Option 2

The delegable check on FirstNameNode during binding validates the data is type of IExternalDelegatableSymbol , but from this scenario, IExternalCdsDataSource is not implanted this interface. So always returns IsServerDelegatable false.
I decided to add the implantation to align with IsPagable.

https://github.com/microsoft/Power-Fx/blob/0fa19687742caa771c4a8f0716f07005497bec49/src/libraries/Microsoft.PowerFx.Core/Binding/Binder.cs#L688C13-L688C75

https://dev.azure.com/msazure/OneAgile/_workitems/edit/29998102

[yuchenglin]

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[LucGenetier]

✅ No public API change.

[LucGenetier]

✅ No public API change.

[adithyaselv]

can you please add a test like this .

N = DelegableDataSource;

UDF(): DelegableDataSource = N;

N2 = Filter(UDF(), "ColumnName" <> "")

this doesn't work today for the same reasons discussed offline

[yuchenglin]

can you please add a test like this .

N = DelegableDataSource;

UDF(): DelegableDataSource = N;

N2 = Filter(UDF(), "ColumnName" <> "")

this doesn't work today for the same reasons discussed offline

Synced offline. This can be better testing at Client

[yuchenglin]

With option 2,

1. Client tests (code gen) are failing since it will add appendQueryOptionsAsync to original query. From the query itself, the behavior looks isn't changed.
   https://msazure.visualstudio.com/OneAgile/_build/results?buildId=112823118&view=ms.vss-test-web.build-test-results-tab

2. We got a report from Playground. There are some class out there depends on this interface

System.MissingMethodException: Method not found: 'Boolean Microsoft.PowerFx.Core.Entities.IExternalDataSource.get_IsDelegatable()'.
at Microsoft.PowerFx.Dataverse.DelegationIRVisitor.Visit(ResolvedObjectNode node, Context context)

[LucGenetier]

✅ No public API change.

[adithyaselv]

    public bool IsDelegatable => _binding.IsDelegatable(_binding.Top);

is it possible to just get rid of this property and directly call _binding.IsDelegatable(_binding.Top) below .

this pattern makes sense for FirstNameNodes - refer binder . but for UDF binder can just use IsServerDelegatable method to determine delegability . i dont think this is used anywhere , can you check ?

this pattern may not be needed here at all . can you investigate ?

---

Refers to: src/libraries/Microsoft.PowerFx.Core/Functions/UserDefinedFunction.cs:47 in 6d3adac. [](commit_id = 6d3adac, deletion_comment = False)

[yuchenglin]

    public bool IsDelegatable => _binding.IsDelegatable(_binding.Top);

is it possible to just get rid of this property and directly call _binding.IsDelegatable(_binding.Top) below .

this pattern makes sense for FirstNameNodes - refer binder . but for UDF binder can just use IsServerDelegatable method to determine delegability . i dont think this is used anywhere , can you check ?

this pattern may not be needed here at all . can you investigate ?

Refers to: src/libraries/Microsoft.PowerFx.Core/Functions/UserDefinedFunction.cs:47 in 6d3adac. [](commit_id = 6d3adac, deletion_comment = False)

Looks like IsServerDelegatable is the common entry point for functions. I've updated the code.

[LucGenetier]

✅ No public API change.

[LucGenetier]

✅ No public API change.