Better conversion from expression should prefer delegate types with non-void return type

[jcouv]

The following code is disallowed by the spec, but allowed by the Microsoft 4.0 spec and the roslyn compiler.

using System;
C.M(null); // bound to M(Func<int>)

public class C
{
    public static void M(Func<int> func) {}
    public static void M(Action action) {}
}

In that version, the “Better conversion from Expression” contains this as part of the tie breakers to determine that D1 is better than D2:

• E is an anonymous function, T1 is either a delegate type D1 or an expression tree type Expression, T2 is either a delegate type D2 or an expression tree type Expression and one of the following holds:
  • D1 is a better conversion target than D2.
  • D1 and D2 have identical parameter lists, and one of the following holds:
    • D1 has a return type Y1, and D2 has a return type Y2, an inferred return type X exists for E in the context of that parameter list, and the conversion from X to Y1 is better than the conversion from X to Y2.
    • D1 has a return type Y, and D2 is void returning.

That final bullet is no longer in 12.6.4.7 (better conversion target) or 12.6.4.5 (better conversion from expression). I wonder if it was dropped erroneously these rules were broken up between “exactly matching expression” and “Better conversion from expression”?

Thanks @BillWagner for digging up this reference.