Mercurial and Heptapod short tutorial¶
Mercurial is a free, distributed source control management tool. We use it for PyPy, not only because it is written in Python, but because its branch model fits our development process better than Git’s branch model.
There are a lot of tutorials and documentations about Mercurial (for example the official Mercurial tutorial). This page is meant to show you what you need to get going with PyPy development.
Heptapod is a friendly fork of GitLab Community Edition supporting Mercurial.
With TortoiseHG (simple for Windows)¶
Download the installer from https://tortoisehg.bitbucket.io/. (but note you might need the evolve extension)
With conda (cross-platform, recommended for Linux and macOS)¶
On Windows, macOS and Linux, one can use
conda (installed with miniconda) to install Mercurial with
few extensions (hg-evolve and hg-git). On Windows, these commands have to be run in the
Anaconda Prompt. First, we need to install conda-app in the base conda environment:
conda activate base python -mpip install conda-app
Then, with the conda-forge channel added (
conda config --add channels
conda-forge), one just needs to run:
conda-app install mercurial
Open a new terminal and the Mercurial command
hg should be available.
If you don’t use TortoiseHG, you should really install the visual diff and merge tool Meld!
You need to create a file
~/.hgrc. For a good starting point, you can use
hg config --edit
An example of configuration file:
[ui] username=myusername <firstname.lastname@example.org> editor=emacs -nw tweakdefaults = True [extensions] hgext.extdiff = # only to use Mercurial with GitHub and Gitlab hggit = # more advanced extensions (really useful for PyPy dev) churn = shelve = rebase = absorb = evolve = topic = [extdiff] cmd.meld =
The line starting with hggit is optional and enables the extension hg-git. This extension is useful to work on projects using Git, for example hosted on Github and Gitlab.
For occasional contribution to PyPy, the evolve and topic extensions have to be installed and activated since we use topic branches for short-term development
To get help on Mercurial, one can start with:
or for a specific command (here
hg help clone
To make a copy of an existing repository:
hg clone https://foss.heptapod.net/pypy/pypy
To get a summary of the working directory state:
Before you begin work, open a new topic branch:
hg topic my_branch
To show changed files in the working directory:
If you add new files or if you deleted files:
hg add name_of_the_file hg remove name_of_the_file
Each time you do some consistent changes:
hg commit -m "A message explaining the commit"
After a commit command
hg st to check that you did
what you wanted to do. If you are unhappy with the commit, you can amend it
with another commit with:
hg commit --amend
To push the state of your working repository to your repository on the web:
The inverse command (pull all commits from the remote repository) is:
Get the last version of a code¶
First pull all the changesets from the remote repository:
Then update the code to the tip:
hg up. You can also directly do:
hg pull -u
Read the history¶
You can get a list of the changesets with:
hg log --graph
hg log -G. With the
-G option, the revisions are
shown as an ASCII art.
Update the code to an old revision¶
hg up 220 to update to the revision 220. We can use a tag, bookmark,
topic name or branch name instead of a number. To get a clean copy, add the
Create a repository from a directory¶
Create a new repository in the given directory by doing:
Merge-Request based workflow with hg-evolve¶
We now use a Merge-Request (MR) based workflow
GitLab’s “merge requests” are equivalent to GitHub’s “pull requests”.
In contrast to the standard workflow in Github, Gitlab and Bitbucket, you don’t need to fork the repository to create Merge Requests.
Instead, you need to become a “developer” of the project. The developers have the permission to push changesets (i.e. “commits”) in a topic in the main repository (for example https://foss.heptapod.net/pypy/pypy). To acquire the “developer” role, please send a message in an issue or if needed, create a dedicated issue.
Topics are used in Mercurial for “lightweight branches” (like Git branches).
The principle is that you first create a topic (with
hg topic). Once a
topic is activated, the changesets created belong to this topic. The new
changesets gathered in a topic can be pushed in the main repository. Even after
having been pushed to the main repository, they stay in the
(which means they can be modified, as opposed to
public changesets. Run
hg help phases for more info).
To list the topics:
To activate a topic already created:
hg up the_name_of_the_topic
To deactivate the topic and come back to the tip of the default branch:
hg up default
To get the list of the changesets in the active topic (very useful):
Developers have to create Merge Requests (MR) to get things merged in the
targeted branch (at the time of writing:
default for Python2.7 or RPython
py3.6 for Python 3.6,
py3.7 for Python 3.7). Let’s present
an example. A developer can do (here, we use ssh but you can also use https):
hg clone ssh://email@example.com/pypy/pypy hg up default hg topic fix_something hg commit -m "Fix a bug related to ..." hg push
Mercurial is going to print an URL to create the associated MR. Once created, the MR should then be reviewed by a contributor with the “maintainer” or higher role. Only maintainers have the permissions to merge a MR, i.e. to publish changesets. The maintainer can tell you how to modify your MR and can also directly modify the changesets of the MR.
We strongly advice to install and activate the evolve, rebase and absorb
extensions locally (see the example of
.hgrc above). This gives a very nice
user experience for the MRs, with the ability to modify a MR with
and safe history editing.
hg absorb is very useful during code review. Let say that a developer
submitted a MR containing few commits. As explained in this blog post,
hg absorb is a mechanism to automatically and intelligently incorporate
uncommitted changes into prior commits. Edit the files to take into account
the remarks of the code review and just run:
hg absorb hg push
and the MR is updated!
If you are asked to “rebase” your MR, it should work with the following commands:
hg pull hg up name_of_my_topic hg rebase hg push
Working with hggit and Github¶
To clone a git repository using hg:
hg clone git+ssh://firstname.lastname@example.org/numpy/numpy
hg clone https://github.com/numpy/numpy
Git branches are represented as Mercurial bookmarks so such commands can be useful:
hg log --graph hg up master hg help bookmarks # list the bookmarks hg bookmarks # put the bookmark master where you are hg book master # deactivate the active bookmark (-i like --inactive) hg book -i
book correspond to the same
If a bookmark is active,
hg pull -u or
hg up will move the bookmark
to the tip of the active branch. You may not want that so it is important to
always deactivate an unused bookmark with
hg book -i or with
Do not forget to place the bookmark
master as wanted.
Delete a bookmark in a remote repository (close a remote Git branch)¶
With Mercurial, we can do:
hg bookmark --delete <bookmark name> hg push --bookmark <bookmark name>
Unfortunately, it does not work for a remote Git repository (with hg-git). We have to use a Git client, clone the repository with Git and do something like:
# this deletes the branch locally git branch --delete <branch name> # this deletes the branch in the remote repository git push origin --delete <branch name>