D2057: translate base85.c into rust code

[indygreg (Gregory Szorc)]

indygreg added a comment.


  Yes, we should definitely split things into multiple crates. Small, narrowly-focused crates does seem to be the Rust way, after all.
  
  `hgcli` should be for things specific to the Rust implementation of `hg`. I think this can also include the feature set of `chg` (once we've ported `chg` to Rust).
  
  I definitely support separating the "pure Rust" from the "Python Rust" via a crate boundary. It is generally useful to have Rust that isn't bound to Python because it will facilitate reuse outside of Python contexts. For example, someone could implement a Mercurial wire protocol server in pure Rust without needing to worry about Python. Of course, we're likely to encounter areas where we really want tight coupling in order to achieve optimal performance in Python. So we may have to design APIs on the pure Rust side to facilitate CPython use. I'm OK with that.
  
  As for how many crates to have, I don't have super strong opinions. I could see us putting every little component/subsystem in its own crate. I could also see us putting everything in one large crate. I don't think it is worth deciding at this early juncture. API design and ability to be reused outside its originally intended purpose is the important property to strive for. I think that has more to do with how the code is authored rather than which crates things are in.
  
  A missing piece of this patch is the build system and module loader integration. We have a //module policy// that dictates which implementation of a Python module we use. We probably want to introduce a `rust` policy that uses Rust-based modules where available and falls back to the `cext` modules/policy if a Rust module isn't available. We also need to figure out how to integrate Rust into `setup.py`. But I think the build system bit can be deferred until we're actually ready to ship Rust, which is still a bit of ways off. I'm happy for the workflow to be //run cargo in order to load Rust modules// for the time being. But if you can implement `Makefile` and/or `setup.py` integration to build these Rust extensions, that would be awesome.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D2057

To: Ivzhh, #hg-reviewers
Cc: indygreg, durin42, kevincox, mercurial-devel