repository: define interface for local repositories Per discussions on the mailing list and at the 4.4 and 4.6 sprints, we want to start defining interfaces for local repository primitives so that we a) have a better idea of what the formal interface for various types is b) can more easily introduce alternate implementations of various components (e.g. in Rust). We have previously implemented interfaces that declare the peer and wire protocol APIs using the abc module. This commit introduces a monolithic interface for the localrepository class. It uses zope.interface - not abc - for defining and declaring the interface. The newly defined "completelocalrepository" interface is objectively horrible. It is based on what is actually in localrepository and doesn't represent a reasonable interface definition IMO. There's lots of... unwanted garbage in the interface. In other words, it reflects the horrible state of the localrepository "god object." But this is fine: a goal of this commit is to get the interface defined so that we have an interface. Future commits can refactor the interface into sub-interfaces, remove unwanted public attributes, etc. I attempted to define reasonable docstrings for the various interface members. But there are so many of them and I didn't know what some are used for. So I was lazy in a number of places and didn't write docstrings or detailed usage docs. Also, the members of the interface are defined in the order they are declared in localrepo.py. This revealed that the grouping of things in localrepo.py is... odd. The localrepository class now declares that it implements our newly defined interface. Unlike abc, zope.interface doesn't check interface conformance at type creation time (abc uses __metaclass__ magic to validate interface conformance when a type is created - usually at module import time). It does provide some functions for validating class and object conformance with declared interfaces. We add these checks to test-check-interfaces.py. We /could/ validate at run-time. But we hold off for now. (I'm a bit scared of doing that because of the various ways extensions monkeypatch repo instances.) After this commit, test-check-interfaces.py will fail if the set of public attributes on the localrepository class or instances change without corresponding updates to the interface. This is by design. Differential Revision: https://phab.mercurial-scm.org/D2933