Summary:
The idea is that the pure Rust revlogindex crate can implement the DagAlgorithm
interface so we will have a consistent interface in the code base that works
for both the existing storage (revlog) and the new segmented changelog.
The other way to do this is to implement the `bindings.dag.namedag` interface
in pure Python for the revlog-based DAG, or supporting quite different
interfaces (ex. revlog DAG and the Rust segmented changelog DAG) in the code
base. At present, I think implementing the Rust DAG traits for revlog is the
most appealing, partially because we already have some key algorithms
implemented (ex. prefix lookup, common ancestors, etc).
Reviewed By: sfilipco
Differential Revision: D21626197
fbshipit-source-id: 733b1af1bcd5fc0784764fc7103412988894d43b
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).
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