# Producing Patches with Mercurial¶

If you are editing or adding to Sage’s core library, you will probably want to share your changes with other users. Mercurial is the tool to do this. Mercurial is the source control system that is included with Sage. This chapter provides an overview of how to use Mercurial with Sage; see http://www.selenic.com/mercurial/ for full documentation on Mercurial.

All of the Mercurial repositories related to Sage are included with Sage. Thus the complete change history and setup for doing development is available in your copy of Sage.

Before using Mercurial, make sure to define your username so the patches you make are identified as yours. Make a file ~/.hgrc in your home directory like this one:

[ui]
username = Euclid of Alexandria <euclid@alexandria.edu>

## Quick Mercurial tutorial for Sage¶

To submit your changes to the Sage development team for refereeing (and inclusion into Sage if the referee’s report is positive), you should produce patch files using Mercurial. The simplest way is to run Mercurial from within Sage following the examples below (note: Hg is the chemical symbol for mercury).

• Type hg_sage.status() and hg_sage.diff() to see exactly what you have done. Use the command q to quit the diff.

Warning

As noted in Coding in Cython, if you have added a Cython file, you also need to edit SAGE_ROOT/devel/sage/module_list.py. If you have added a new directory, you need to edit SAGE_ROOT/devel/sage/setup.py. If you have added something other than Python or Cython files, then you might need to add entries to the file SAGE_ROOT/devel/sage/MANIFEST.in: this records all of the files to include in distributions of the Sage library. Look at the file itself for examples, and see the Python documentation http://docs.python.org/distutils/sourcedist.html#specifying-the-files-to-distribute for all of the details.

• Commit your changes by typing hg_sage.commit() to commit the changes in files to the repository. If you want to commit only specific files, each file must be listed individually with full path names, e.g. hg_sage.commit('sage/misc/misc.py  sage/all.py'). If no file names are given, all changed files are committed. First, the output of hg diff is displayed: look at it or just enter q. Then you are dumped into an editor to type a brief comment on the changes. The default editor is vi, so type i to insert, write a one line commit message of the form trac xxxx: <your-commit-message-here> where xxxx is the Sage development tracking system ticket number (see http://trac.sagemath.org). To quit the vi editor and save your commit message, hit Escape and type :wq. (In bash, to make emacs the default editor, type export EDITOR=emacs.)

• Now create a patch file using hg_sage.export(...). This command needs a revision number (or list of revision numbers) as an argument; use hg_sage.export('tip') to use the most recent revision number or use hg_sage.log() to see all these numbers. An optional second argument to hg_sage.export(...) is a file name for the patch. The default is (changeset_revision_number).patch, which is written in what Sage considers the current directory (this can be found with the command os.path.abspath('.')).

• Then post your patch on the Sage Trac server: see The Sage Trac Server: Submitting Patches and Packages.

You can also run Mercurial directly from the command line using the command sage -hg. Or you can start a very nice web server that allows you to navigate your repository with a web browser, or pull patches from it remotely, by typing hg_sage.serve(). Then open your web browser and point it to http://localhost:8000, which is the default listening address for Mercurial.

Finally, if you want to apply a patch file (perhaps you have downloaded a patch from the Trac server for review), use the command hg_sage.patch('filename') (or hg_sage.apply('filename') for hg bundle files).

Before you modify Sage library files, you might want to create a copy of the Sage library in which to work. Do this by typing sage -clone myver, for example. Then Sage will use Mercurial to clone the current repository and call the result myver. The new repository is stored in <SAGE_ROOT>/devel/sage-myver, and when you clone, the symbolic link sage --> sage-myver is made.

(You can also do, e.g. sage -clone -r 1250 oldver, to get a clone of Sage as it was at revision 1250. Of course, dependency issues could make old versions not work (e.g. maybe an old Sage library would not compile with the latest Singular library, which is what is installed elsewhere in SAGE_ROOT). From within Sage, type hg_sage.log() to see the revision history. Note that if you clone an old version, all of the Cython code is rebuilt, since there is no easy way to know which files do and do not need rebuilding.)

Once you have copied the library to a new branch myver and edited some files there, you should build the Sage library to incorporate those changes. Type sage -b myver, or just sage -b if the branch myver is already the current branch, i.e. if SAGE_ROOT/devel/sage links to SAGE_ROOT/devel/sage-myver. You can also type sage -br myver to build the library and then to immediately run Sage.

## Using Mercurial with other Sage repositories¶

Sage includes these Mercurial repositories:

• SAGE_ROOT/devel/sage-*: the Sage library source code.
• SAGE_ROOT/devel/ext: external system code, i.e. code included with Sage that is written for the systems with which Sage interfaces, e.g. GAP, PARI, etc.
• SAGE_ROOT/local/bin: Sage shell scripts.
• SAGE_ROOT: Sage root – text files in the main Sage directory and in SAGE_ROOT/spkg.

The previous section discussed using Mercurial with the Sage library, via the command hg_sage. There are corresponding commands for each of the repositories:

• use hg_sage for the Sage library
• use hg_extcode for the external system code
• use hg_scripts for the Sage shell scripts.
• use hg_root for the Sage root.

Since version 3.4, both the Sage library and documentation repositories are managed by the command hg_sage.