contrib/chg/README

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

cHg
===

A fast client for Mercurial command server running on Unix.

Install:

 $ make
 $ make install

Usage:

 $ chg help                 # show help of Mercurial
 $ alias hg=chg             # replace hg command
 $ chg --kill-chg-daemon    # terminate background server

Environment variables:

Although cHg tries to update environment variables, some of them cannot be
changed after spawning the server. The following variables are specially
handled:

 * configuration files are reloaded automatically by default.
 * CHGHG or HG specifies the path to the hg executable spawned as the
   background command server.

The following variables are available for testing:

 * CHGDEBUG enables debug messages.
 * CHGSOCKNAME specifies the socket path of the background cmdserver.
 * CHGTIMEOUT specifies how many seconds chg will wait before giving up
   connecting to a cmdserver. If it is 0, chg will wait forever. Default: 60