Adding support for default interface function members

[RexJaeschke]

Re the MS proposal: The main challenge when reading it was the (misleading) occurrence of the modifier override in numerous examples and narrative. As best as I can tell, this modifier is not actually permitted on any interface member. Instead, overriding is achieved via explicit implementation.

There is one open question, which has to do with the topic "Base Interface Invocations," for which the decision "Decided on base(N.I1<T>).M(s)" was made. However, as far as I can tell, support for this was not added to the V8 compiler. Can someone please confirm (or refute) that.

BTW, I think the proposal is misnamed: it really applies to all interface function members (properties, indexers, and events as well), not just methods. (it also allows nested types.)

Note: No spec changes are needed to support entry point Main in an interface. Any non-generic type containing a Main method with void/int return and no/one string[] parameter list is already permitted, which not only allows Main in a struct or class, but now also in an interface.

[RexJaeschke]

Depending how PR #680 is resolved, some tweaks might be needed with this PR.

As at 2024-01-11, that PR is still pending, and is tied to the review of this PR.

[BillWagner]

rebased on the latest draft-v8 on 09-23-2023

[KalleOlaviNiemitalo]

Should the references to "C# implementations targeting the CLI" be changed somehow because the ECMA standard CLI does not support default interface members? Possible answers include:

• Remove them; C# 8 implementations cannot target "the CLI".
• Change them to say "targeting a CLI with extensions" or the like.
• Keep them; a C# implementation can still target the standard CLI, although the mapping may become complex or inefficient or have restrictions (like not supporting dynamic loading of assemblies that were not provided at build time).