Summary:
A common pattern in Mercurial's data storage layer Python bindings is to have a Python object that wraps a Rust object. These Python objects are often passed across the FFI boundary to Rust code, which then may need to access the underlying Rust value.
Previously, the objects that used this pattern did so in an ad-hoc manner, typically by providing an `into_inner` or `to_inner` inherent method. This diff introduces a new `ExtractInner` trait that standardizes this pattern into a single interface, which in turn allows this pattern to be used with generics.
Reviewed By: quark-zju
Differential Revision: D22429347
fbshipit-source-id: cab4c24b8b98c6ef8307f72a9b4726aabdc829cc
Any native code (C/C++/Rust) that Mercurial (either core or extensions)
depends on should go here. Python code, or native code that depends on
Python code (e.g. #include <Python.h> or use cpython) is disallowed.
As we start to convert more of Mercurial into Rust, and write new paths
entrirely in native code, we'll want to limit our dependency on Python, which is
why this barrier exists.
See also hgext/extlib/README.md, mercurial/cext/README.mb.
How do I choose between lib and extlib (and cext)?
If your code is native and doesn't depend on Python (awesome!), it goes here.
Otherwise, put it in hgext/extlib (if it's only used by extensions) or
mercurial/cext (if it's used by extensions or core).