Expose IEventSymbol.AssociatedField

[JohanLarsson]

public class C
{
    public event EventHandler E;
}

Given ^ type.GetMebres() does not return the backing field of the event. See #36259

And IEventSymbol does not expose AssociatedField

Is there a way to get the field for a third party analyzer?

[jnm2]

Use case: DotNetAnalyzers/ReflectionAnalyzers#206

[gafter]

We currently treat auto-properties and field-like events differently: for the former we have a field in the set of members, and for the latter we do not. I think this is an artifact of the history of the compiler rather than an explicit design choice. In both cases the language specification explicitly calls out the existence of an underlying field.

[jnm2]

@gafter Right now with events, third-party analyzers are out to dry. There is no Roslyn API to show the existence of an event backing field.

@CyrusNajmabadi makes the point in #42355 (comment) that such a public API would be desirable even if there was currently another way to access the info. In the case of events, there is no current way to access backing field info.