Status of the "port" of Mercurial to Py3k

This document describes the current status of mercurial's Py3k port. The work here described was developed as part of the Google Summer of Code 2010 program.

Summary

Last milestone: "hg manifest" runs successfully.

Current development: Documentation & Improvement of the fixers to generalize the manual edits

Objective and constraints

This project's objective is quite clear: to "port" mercurial to py3k. "Port" is between quotes because this is not a complete portm or a rewrite: we want to make mercurial run in py3k while maintaining compatibility with python 2.x. There is an additional constraint, though: mercurial supports python from 2.4, which means the features introduced in 2.6 to ease the porting process can't really be used in the port. Also, refactoring the code to work in both python 2 and 3 proved to be too much work because:

1. It would be troublesome to make a multipython code;
2. It would be a maintenance hell.

Thus, we came to the conclusion that extending 2to3, the python refactoring tool, was the way to go. So, to summarize the port's objective and constraints:

• We want to make hg run on py3k;
• 2to3 is being used for that;
• We must maintain support for python 2.4 and above;

An important aspect of the approach taken is that we stick to a "from the inside out approach". This means we started working on a port of the core C modules, then to the extension C modules (inotify only, currently), then removing most warnings issued by python 2.6 in "3 mode" (a mode that that issues warnings for deprecated modules and other incompatible changes) to, then, work on the fixing of the code.

Current implementation

Source code

Most of the code developed in this project has been already imported into mercurial's official repository. Which means that pulling from it will give you updated code that is known to mostly work. Additionally, you can clone Renato Cunha's patch queue, if you want to test more experimental code and code that hasn't been imported to mercurial yet.

How to run it

From mercurial's source root, you can run:

python3 contrib/setup3k.py build_ext -i build_py -c -d . build_mo

this is equivalent to running "make local" in hg's source root, with the difference that the python3 interpreter will be used and that the python source code will be preprocessed by 2to3 before exiting. This command takes approximately three minutes to run on a five year-old Athlon64 3000+.