diff rust/hg-cpython/src/lib.rs @ 41052:4c25038c112c

rust-cpython: implement Graph using C parents function

We introduce the `Index` struct that wraps the C index. It is
not intrinsically protected by the GIL (see the lengthy
discussion in its docstring). Improving on this seems
prematurate at this point.

A pointer to the parents function is stored on the parsers
C extension module as a capsule object.

This is the recommended way to export a C API for consumption
from other extensions.
See also: https://docs.python.org/2.7/c-api/capsule.html

In our case, we use it in cindex.rs, retrieving function
pointer from the capsule and storing it within the CIndex
struct, alongside with a pointer to the index. From there,
the implementation is very close to the one from hg-direct-ffi.

The naming convention for the capsule is inspired from the
one in datetime:

  >>> import datetime
  >>> datetime.datetime_CAPI
  <capsule object "datetime.datetime_CAPI" at 0x7fb51201ecf0>

although in datetime's case, the capsule points to a struct holding
several type objects and methods.

Differential Revision: https://phab.mercurial-scm.org/D5438

--- a/rust/hg-cpython/src/lib.rs	Thu Dec 20 22:28:39 2018 -0500
+++ b/rust/hg-cpython/src/lib.rs	Mon Dec 03 07:44:08 2018 +0100
@@ -21,8 +21,10 @@
 #[macro_use]
 extern crate cpython;
 extern crate hg;
+extern crate libc;
 
 mod ancestors;
+mod cindex;
 mod exceptions;
 
 py_module_initializer!(rustext, initrustext, PyInit_rustext, |py, m| {