LilyPond Contributor's Guide: 3.3.4 Commits and patches

### 3.3.4 Commits and patches

#### Understanding commits

Technically, a commit is a single point in the history of a branch, but most developers use the term to mean a commit object, which stores information about a particular revision. A single commit can record changes to multiple source files, and typically represents one logical set of related changes (such as a bug-fix). You can list the ten most recent commits in your current branch with this command:

>     git log -10 --oneline

If you’re using an older version of Git and get an ‘unrecognized argument’ error, use this instead:

>     git log -10 --pretty=oneline --abbrev-commit

More interactive lists of the commits on the remote `master` branch are available at http://git.sv.gnu.org/gitweb/?p=lilypond.git;a=shortlog and http://git.sv.gnu.org/cgit/lilypond.git/log/.

#### Making commits

Once you have modified some source files in your working directory, you can make a commit with the following procedure:

1. Make sure you’ve configured Git properly (see Configuring Git). Check that your changes meet the requirements described in Code style and/or Documentation policy. For advanced edits, you may also want to verify that the changes don’t break the compilation process.
2. Run the following command:

   >     git status

   to make sure you’re on the right branch, and to see which files have been modified, added or removed, etc. You may need to tell Git about any files you’ve added by running one of these:

   >     git add file  # add untracked file individually
   >     git add .     # add all untracked files in current directory

   After `git add`, run `git status` again to make sure you got everything. You may also need to modify ‘`GNUmakefile`’.

3. Preview the changes about to be committed (to make sure everything looks right) with:

   >     git diff HEAD

   The `HEAD` argument refers to the most recent commit on the currently checked-out branch.

4. Generate the commit with:

   >     git commit -a

   The `-a` is short for `--all` which includes modified and deleted files, but only those newly created files that have previously been added.

#### Commit messages

When you run the `git commit -a` command, Git automatically opens the default text editor so you can enter a commit message. If you find yourself in a foreign editing environment, you’re probably in `vi` or `vim`. If you want to switch to an editor you’re more familiar with, quit by typing `:q!` and pressing `<Enter>`. See Configuring Git for instructions on changing the default editor.

In any case, Git will open a text file for your commit message that looks like this:

>     # Please enter the commit message for your changes.  Lines starting
>     # with '#' will be ignored, and an empty message aborts the commit.
>     # On branch master
>     # Changes to be committed:
>     #   (use "git reset HEAD <file>..." to unstage)
>     #
>     #	modified:   working.itexi
>     #

Your commit message should begin with a one-line summary describing the change (no more than 50 characters long), and if necessary a blank line followed by several lines giving the details:

>     Doc: add Baerenreiter and Henle solo cello suites

>     Added comparison of solo cello suite engravings to new essay with
>     high-res images, fixed cropping on Finale example.

Commit messages often start with a short prefix describing the general location of the changes. If a commit affects the documentation in English (or in several languages simultaneously) the commit message should be prefixed with “Doc: ”. If the commit affects only one of the translations, the commit message should be prefixed with “Doc-**: ”, where ** is the two-letter language code. Commits that affect the website should use “Web: ” for English, and “Web-**: ” for the other languages. Also, changes to a single file are often prefixed with the name of the file involved. Visit the links listed in Understanding commits for examples.

#### Making patches

If you want to share your changes with other contributors and developers, you need to generate patches from your commits. We prefer it if you follow the instructions in Uploading a patch for review. However, we present an alternate method here.

You should always run `git pull -r` (translators should leave off the `-r`) before doing this to ensure that your patches are as current as possible.

Once you have made one or more commits in your local repository, and pulled the most recent commits from the remote branch, you can generate patches from your local commits with the command:

>     git format-patch origin

The `origin` argument refers to the remote tracking branch at `git.sv.gnu.org`. This command generates a separate patch for each commit that’s in the current branch but not in the remote branch. Patches are placed in the current working directory and will have names that look something like this:

>     0001-Doc-Fix-typos.patch
>     0002-Web-Remove-dead-links.patch
>     ⋮

Send an email (must be less than 64 KB) to lilypond-devel@gnu.org briefly explaining your work, with the patch files attached. Translators should send patches to translations@lilynet.net. After your patches are reviewed, the developers may push one or more of them to the main repository or discuss them with you.

#### Uploading a patch for review

Any non-trivial change should be uploaded to our “Rietveld” code review website:

>     http://codereview.appspot.com/

#### `git-cl` install

LilyDev users should skip over these ‘install’ instructions.

1. Install `git-cl` by entering:

   >     git clone git://neugierig.org/git-cl.git

2. Add the ‘`git-cl/`’ directory to your PATH, or create a symbolic link to the `git-cl` and `upload.py` scripts in one of your PATH directories (such as ‘`$HOME/bin`’).

#### `git-cl` configuration

LilyDev users should perform these ‘configuration’ instructions.

1. You must have a gmail account; please create one if you do not have one already.
2. Move into the top source directory and then configure `git cl` with the following commands. If you do not understand any question, just answer with a newline (CR).

   >     cd $HOME/lilypond-git/
   >     git cl config

   The “CC list” question should be answered with:

   >     lilypond-devel@gnu.org

#### Uploading patch set

Note: Unless you are familiar with branches, only work on one set of changes at once.

There are two methods, depending on your git setup.

- Master branch: (easy option, and used in `lily-git.tcl`)

  If you added your patch to `master`, then:

  >     git pull -r
  >     git cl upload origin/master

  If you have git push ability, make sure that you remove your patch (with `git rebase` or `git reset`) before pushing other stuff.

- Separate branch: (complicated option)

  Ensure your changes are committed in a separate branch, which should differ from the reference branch to be used by just the changes to be uploaded. If the reference branch is to be origin/master, ensure this is up-to-date. If necessary, use git rebase to rebase the branch containing the changes to the head of origin/master. Finally, check out branch with the changes and enter the command:

  >     git cl upload <reference SHA1 ID>

  where <reference SHA1 ID> is the SHA1 ID of the commit to be used as a reference source for the patch. Generally, this will be the SHA1 ID of origin/master, and in that case the command:

  >     git cl upload origin/master

  can be used.

After prompting for your Google email address and password, the patch set will be posted to Rietveld, and you will be given a URL for your patch.

Note: Some installations of git-cl fail when uploading a patch set that includes a .scm file. When this happens, it can generally be fixed by editing the file ‘`/etc/mime.types`’. Add a line to this file containing `text/x-script.scheme scm`.

#### Announcing your patch set

You should then announce the patch by logging into the code review issue webpage and using “Publish + Mail Comments” to add a (mostly bogus) comment to your issue. The text of your comment will be sent to our developer mailing list.

Note: There is no automatic notification of a new patch; you must add a comment yourself.

#### Revisions

As revisions are made in response to comments, successive patch sets for the same issue can be uploaded by reissuing the git-cl command with the modified branch checked out.

Sometimes in response to comments on revisions, the best way to work may require creation of a new branch in git. In order to associate the new branch with an existing Rietveld issue, the following command can be used:

>     git cl issue issue-number

where `issue-number` is the number of the existing Rietveld issue.

#### Resetting git cl

If `git cl` becomes confused, you can “reset” it by running:

>     git cl issue 0

#### LilyPond — Contributor’s Guide