Add support for default interface members in inheritance-based proxy types #661

... instead of `MethodBase`s to identify which methods get invoked. This should make tests easier to read & understand.

Two of these tests are failing: * Class proxies cannot intercept interface methods with a default implementation if the proxied class type does not override it. * Interface proxies cannot proceed to default implementations.

A class implementing an interface with default method implementations will not necessarily override those methods; in such cases, the methods are currently "invisible" to DynamicProxy and thus won't get proxied. This can be solved by an extra pass over all interfaces to collect such methods, as is done in this commit. Ideally we wouldn't have to iterate over all interfaces more than once, so we should next make an effort to limit the runtime impact of this extra pass.

Assuming that default interface methods are relatively rare, if we keep track of which interfaces contain any of them at all, we can then limit our extra pass during class proxy generation to just those interfaces and exclude the rest (i.e. hopefully the majority). Additionally, our collector may skip some of the more expensive checks by bailing out for methods it isn't actually interested in.

... by properly forwarding the "standalone" flag in the newly added collector.

Those essentially target "mixed" scenarios where default implementations show up next to "regular" methods. This is to better ensure that the new code paths will not interfere with pre-existing logic.

The code changes we made do not suggest that pre-existing logic dealing with generics might somehow no longer work, however we did add a bit of new code for generics which we should target with at least one test.

This includes a test for `static abstract` methods that remains ignored for now, since we haven't implemented support for this C# 11 language feature, nor do we target any runtimes that support it. (The test is being added as a future reminder, once we start targeting .NET 7+.)

A few of these tests fail due to `Debug.Assert` failures in `Interface- MembersWithDefaultImplementationCollector`.

`sealed` methods do not show up in interface mappings, so make sure `InterfaceMembersWithDefaultImplementationCollector` can deal with them anyway in case of interfaces that contain both `sealed` methods as well as overridable ones with a default implementation.

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Add support for default interface members in inheritance-based proxy types #661

Add support for default interface members in inheritance-based proxy types #661

Commits on Sep 10, 2023