rust-dirstate: rust implementation of dirstatemap The `dirstatemap` is one of the last building blocks needed to get to a `dirstate.walk` Rust implementation. Disclaimer: This change is part of a big (10) series of patches, all of which started as one big changeset that took a long time to write. This `dirstatemap` implementation is a compromise in terms of complexity both for me and for the reviewers. I chose to submit this patch right now because while it is not perfect, it works and is simple enough (IMHO) to be reviewed. The Python implementation uses a lot of lazy propertycaches, breaks encapsulation and is used as an iterator in a lot of places, all of which dictated the somewhat unidiomatic patterns in this change. Like written in the comments, rewriting this struct to use the typestate pattern might be a good idea, but this is a good first step. Differential Revision: https://phab.mercurial-scm.org/D6632

rust-cpython: add macro for sharing references Following an experiment done by Georges Racinet, we now have a working way of sharing references between Python and Rust. This is needed in many points of the codebase, for example every time we need to expose an iterator to a Rust-backed Python class. In a few words, references are (unsafely) marked as `'static` and coupled with manual reference counting; we are doing manual borrow-checking. This changes introduces two declarative macro to help reduce boilerplate. While it is better than not using macros, they are not perfect. They need to: - Integrate with the garbage collector for container types (not needed as of yet), as stated in the docstring - Allow for leaking multiple attributes at the same time - Inject the `py_shared_state` data attribute in `py_class`-generated structs - Automatically namespace the functions and attributes they generate For at least the last two points, we will need to write a procedural macro instead of a declarative one. While this reference-sharing mechanism is being ironed out I thought it best not to implement it yet. Lastly, and implementation detail renders our Rust-backed Python iterators too strict to be proper drop-in replacements, as will be illustrated in a future patch: if the data structure referenced by a non-depleted iterator is mutated, an `AlreadyBorrowed` exception is raised, whereas Python would allow it, only to raise a `RuntimeError` if `next` is called on said iterator. This will have to be addressed at some point. Differential Revision: https://phab.mercurial-scm.org/D6631