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Mercurial (sometimes referred to as hg) is the source code management system used for Octave development.

Creating and submitting patches (changesets)

Everybody is free to obtain, built, and modify Octave's source code, given in the main repository at If you want to share your modifications, for example to fix a nasty bug #42424, you cannot just submit your changes to Octave's main repository. You have to generate a patch (or changeset) so other Octave developers can include them into Octave's source code.

  1. Get the latest revision of Octave (or some Octave package)
    hg clone
    or when already cloned
    hg pull && hg update
  2. Make your changes (fix bug #42424) and save them. Make sure that your changes don't introduce new bugs! Thus it is recommended to build Octave and to run Octave's test suite before proceeding.
    Warning icon.svg
    Please follow the Contribution guidelines for C/C++ or Octave code files!
  3. Commit your changes
    hg commit
    Mercurial will open your default editor and ask you for a commit message. Please follow the commit message guidelines, e.g.
    help.m: Display relevant topics first (bug #42424)
    * scripts/help/help.m: Describe what you changed to display relevant topics
      first.  The maximal line width is 80 characters.
  4. Export the changes
    hg export -r tip -o bug42424.patch
    The final patch for submission will look like this
    File: bug42424.patch
    # HG changeset patch
    # User Awesome Hacker <>
    # Date 1591780091 -32400
    #      Wed Jun 10 18:08:11 2020 +0100
    # Node ID 68c698c4f2fd98bf2d48234bd1da99e91763114f
    # Parent  f5c9bb5955e7c9fddef5c3c3f115201e11b43b79
    help.m: Display relevant topics first (bug #42424)
    * scripts/help/help.m: Describe what you changed to display relevant topics
      first.  The maximal line width is 80 characters.
    diff -r f5c9bb5955e7 -r 68c698c4f2fd scripts/help/help.m
    --- a/scripts/help/help.m	Tue Jun 09 14:11:13 2020 -0700
    +++ b/scripts/help/help.m	Wed Jun 10 18:08:11 2020 +0900
    @@ -99,7 +99,7 @@ function retval = help (name)
         ## Get help text
    -    [text, format] = get_help_text (name);
    +    [text, format] = get_better_help_text (name);
         ## Take action depending on help text format
         switch (lower (format))
  5. Upload bug42424.patch to the bug or patch tracker. If your patch file is larger than the upload limit, you can compress it before uploading. Please use a free format!

Mercurial Tips for SoC students

This section is meant to provide tips for SOCIS or GSoC students working on new Octave features.

Students should publish their work as it progresses in a public repository merging regularly the main savannah repository to facilitate merging back their code at the end of the project.

Here are some useful hg commands that can be used to do this.

Getting started

  1. Clone the main Octave repository at savannah:
    hg clone
  2. Create a new bookmark:
    hg bookmark student-bookmark-name
  3. Make the bookmark visible in the public repo, assuming the public repo is at
    hg push --bookmark ssh://

Staying up-to-date with the main savannah repository

As the students development proceeds, the savannah repository gets updated, too. To avoid having the two branches diverging too much, which can lead to conflicts when the final merge is done, students should keep their public repo up-to-date with the recent changes, the following commands can be used for this:

  1. Download new changes from the main line of development
    hg pull
  2. Merge the main line of development into the feature branch
    hg up -r student-bookmark-name
    hg merge @
  3. Apply the change and publish it
    hg commit -m "periodic merge of default branch into my branch"
    hg push ssh://

Preparing for code reviews

At the time of the mid-term or final review (or whenever the mentor requires it) students should prepare their code for review and possibly inclusion into the main development branch. To this end students should:

  1. prepare a full log of their changes, listing files that have been touched and including a summary of the purpose of those changes. If students have been following the Commit message guidelines the following command will give a good starting point
    hg log --style=changelog --no-merges --user student-name
    this message should be edited so that
    1. each touched file appears only once
    2. changes that were backed out should not be mentioned

    The main purpose of this log is to make it easy, not only for the main mentor, but also for other developers who have not been closely following the progress of the project to quickly understand where to look at in the code to evaluate it, but it will also be used as the commit message for the merge changeset, so it should itself comply with the Commit message guidelines.

  2. prepare a merge changeset including all the code that should be submitted for review
    1. pull from the main repository
      hg pull
    2. move to the top of the main line of development and merge in the feature branch
      hg up -r @
      hg merge student-bookmark-name
    3. create a changeset, export it and send to the mentor for review, remember to use the log created above as a commit message
      hg commit
      hg export @ > mid-term-review.changeset
      the file mid-term-review.changeset can then be sent to the mailing list or posted to the patch tracker

Example Mercurial configuration

Place the following file in your home directory, e.g. /home/username/.hgrc.

File: .hgrc
username = Your Name <your@email>

color =
histedit =
pager =
rebase =
strip =

pager = LESS='FSRX' less
attend = help, annotate, cat, diff, export, glog, log, outgoing, incoming

showfunc = True

mode = terminfo

## Custom colors
color.gray = 244 = 202
color.lightyellow = 191
color.darkorange = 220
color.brightyellow = 226

status.modified = magenta bold
status.added = green bold
status.removed = red bold
status.deleted = cyan bold
status.unknown = gray bold
status.ignored = gray bold

## Colors for each label
log.branch = cyan
log.summary = lightyellow
log.description = lightyellow
log.bookmark = green
log.tag = darkorange
log.graph = blue

## Colors for each phase
changeset.secret = blue bold
changeset.draft  = red bold
changeset.public = orange = bold blue_background

track.current = True

glog = log --graph
top = log --graph -l

External links