LilyPond Contributor's Guide: 3.5 Git on Windows

## 3.5 Git on Windows

TODO: Decide what to do with this... Pare it down? Move paragraphs next to analogous Unix instructions? -mp

### 3.5.1 Background to nomenclature

Git is a system for tracking the changes made to source files by a distributed set of editors. It is designed to work without a master repository, but we have chosen to have a master repository for LilyPond files. Editors hold a local copy of the master repository together with any changes they have made locally. Local changes are held in a local ‘branch’, of which there may be several, but these instructions assume you are using just one. The files visible in the local repository always correspond to those on the currently ‘checked out’ local branch.

Files are edited on a local branch, and in that state the changes are said to be ‘unstaged’. When editing is complete, the changes are moved to being ‘staged for commit’, and finally the changes are ‘committed’ to the local branch. Once committed, the changes (called a ‘commit’) are given a unique 40-digit hexadecimal reference number called the ‘Committish’ or ‘SHA1 ID’ which identifies the commit to Git. Such committed changes can be sent to the master repository by ‘pushing’ them (if you have write permission) or by sending them by email to someone who has, either as a complete file or as a ‘diff’ or ‘patch’ (which send just the differences from the master repository).

### 3.5.2 Installing git

Obtain Git from http://code.google.com/p/msysgit/downloads/list (note, not msysGit, which is for Git developers and not PortableGit, which is not a full git installation) and install it.

Note that most users will not need to install SSH. That is not required until you have been granted direct push permissions to the master git repository.

Start Git by clicking on the desktop icon. This will bring up a command line bash shell. This may be unfamiliar to Windows users. If so, follow these instructions carefully. Commands are entered at a $ prompt and are terminated by keying a newline.

### 3.5.3 Initialising Git

Decide where you wish to place your local Git repository, creating the folders in Windows as necessary. Here we call the folder to contain the repository `[path]/Git`, but if you intend using Git for other projects a directory name like `lilypond-git` might be better. You will need to have space for around 100Mbytes.

Start the Git bash shell by clicking on the desk-top icon installed with Git and type

>     cd [path]/Git

to position the shell at your new Git repository.

Note: if [path] contains folders with names containing spaces use

>     cd "[path]/Git"

Then type

>     git init

to initialize your Git repository.

Then type (all on one line; the shell will wrap automatically)

>     git remote add -ft master origin git://git.sv.gnu.org/lilypond.git

to download the lilypond master files.

Note: Be patient! Even on a broadband connection this can take 10 minutes or more. Wait for lots of [new tag] messages and the $ prompt.

We now need to generate a local copy of the downloaded files in a new local branch. Your local branch needs to have a name. It is usual to call it ‘master’ and we shall do that here.

To do this, type

>     git checkout -b master origin/master

This creates a second branch called ‘master’. You will see two warnings (ignore these), and a message advising you that your local branch ‘master’ has been set up to track the remote branch. You now have two branches, a local branch called ‘master’, and a tracking branch called ‘origin/master’, which is a shortened form of ‘remotes/origin/master’.

Return to Windows Explorer and look in your Git repository. You should see lots of folders. For example, the LilyPond documentation can be found in [path]/Git/Documentation/.

The Git bash shell is terminated by typing `exit` or by clicking on the usual Windows close-window widget.

### 3.5.4 Git GUI

Almost all subsequent work will use the Git Graphical User Interface, which avoids having to type command line commands. To start Git GUI first start the Git bash shell by clicking on the desktop icon, and type

>     cd [path]/Git
>     git gui

The Git GUI will open in a new window. It contains four panels and 7 pull-down menus. At this stage do not use any of the commands under Branch, Commit, Merge or Remote. These will be explained later.

The top panel on the left contains the names of files which you are in the process of editing (Unstaged Changes), and the lower panel on the left contains the names of files you have finished editing and have staged ready for committing (Staged Changes). At present, these panels will be empty as you have not yet made any changes to any file. After a file has been edited and saved the top panel on the right will display the differences between the edited file selected in one of the panels on the left and the last version committed on the current branch.

The panel at bottom right is used to enter a descriptive message about the change before committing it.

The Git GUI is terminated by entering CNTL-Q while it is the active window or by clicking on the usual Windows close-window widget.

### 3.5.5 Personalising your local git repository

Open the Git GUI, click on

>     Edit -> Options

and enter your name and email address in the left-hand (Git Repository) panel. Leave everything else unchanged and save it.

Note that Windows users must leave the default setting for line endings unchanged. All files in a git repository must have lines terminated by just a LF, as this is required for Merge to work, but Windows files are terminated by CRLF by default. The git default setting causes the line endings of files in a Windows git repository to be flipped automatically between LF and CRLF as required. This enables files to be edited by any Windows editor without causing problems in the git repository.

### 3.5.6 Checking out a branch

At this stage you have two branches in your local repository, both identical. To see them click on

>     Branch -> Checkout

You should have one local branch called ‘master’ and one tracking branch called ‘origin/master’. The latter is your local copy of the ‘remotes/origin/master’ branch in the master LilyPond repository. The local ‘master’ branch is where you will make your local changes.

When a particular branch is selected, i.e., checked out, the files visible in your repository are changed to reflect the state of the files on that branch.

### 3.5.7 Updating files from ‘remote/origin/master’

Before starting the editing of a file, ensure your local repository contains the latest version of the files in the remote repository by first clicking

>     Remote -> Fetch from -> origin

in the Git GUI.

This will place the latest version of every file, including all the changes made by others, into the ‘origin/master’ branch of the tracking branches in your git repository. You can see these files by checking out this branch, but you must never edit any files while this branch is checked out. Check out your local ‘master’ branch again.

You then need to merge these fetched files into your local ‘master’ branch by clicking on

>     Merge -> Local Merge

and if necessary select the local ‘master’ branch.

Note that a merge cannot be completed if you have made any local changes which have not yet been committed.

This merge will update all the files in the ‘master’ branch to reflect the current state of the ‘origin/master’ branch. If any of the changes conflict with changes you have made yourself recently you will be notified of the conflict (see below).

### 3.5.8 Editing files

First ensure your ‘master’ branch is checked out, then simply edit the files in your local Git repository with your favourite editor and save them back there. If any file contains non-ASCII characters ensure you save it in UTF-8 format. Git will detect any changes whenever you restart Git GUI and the file names will then be listed in the Unstaged Changes panel. Or you can click the Rescan button to refresh the panel contents at any time. You may break off and resume editing any time.

The changes you have made may be displayed in diff form in the top right-hand panel of Git GUI by clicking on the file name shown in one of the left panels.

When your editing is complete, move the files from being Unstaged to Staged by clicking the document symbol to the left of each name. If you change your mind it can be moved back by clicking on the ticked box to the left of the name.

Finally the changes you have made may be committed to your ‘master’ branch by entering a brief message in the Commit Message box and clicking the Commit button.

If you wish to amend your changes after a commit has been made, the original version and the changes you made in that commit may be recovered by selecting

>     Commit -> Amend Last Commit

or by checking the Amend Last Commit radio button at bottom right. This will return the changes to the Staged state, so further editing made be carried out within that commit. This must only be done before the changes have been Pushed or sent to your mentor for Pushing - after that it is too late and corrections have to be made as a separate commit.

### 3.5.9 Sending changes to ‘remotes/origin/master’

If you do not have write access to ‘remotes/origin/master’ you will need to send your changes by email to someone who does.

First you need to create a diff or patch file containing your changes. To create this, the file must first be committed. Then terminate the Git GUI. In the git bash shell first cd to your Git repository with

>     cd [path]/Git

if necessary, then produce the patch with

>     git format-patch origin

This will create a patch file for all the locally committed files which differ from ‘origin/master’. The patch file can be found in [path]/Git and will have a name formed from the commit message.

### 3.5.10 Resolving merge conflicts

As soon as you have committed a changed file your local `master` branch has diverged from `origin/master`, and will remain diverged until your changes have been committed in `remotes/origin/master` and Fetched back into your `origin/master` branch. Similarly, if a new commit has been made to `remotes/origin/master` by someone else and Fetched, your local `master` branch is divergent. You can detect a divergent branch by clicking on

>     Repository -> Visualise all branch history

This opens up a very useful new window called ‘gitk’. Use this to browse all the commits made by yourself and others.

If the diagram at top left of the resulting window does not show your `master` tag on the same node as the `remotes/origin/master` tag your branch has diverged from `origin/master`. This is quite normal if files you have modified yourself have not yet been Pushed to `remotes/origin/master` and Fetched, or if files modified and committed by others have been Fetched since you last Merged `origin/master` into your local `master` branch.

If a file being merged from `origin/master` differs from one you have modified in a way that cannot be resolved automatically by git, Merge will report a Conflict which you must resolve by editing the file to create the version you wish to keep.

This could happen if the person updating `remotes/origin/master` for you has added some changes of his own before committing your changes to `remotes/origin/master`, or if someone else has changed the same file since you last fetched the file from `remotes/origin/master`.

Open the file in your editor and look for sections which are delimited with ...

[to be completed when I next have a merge conflict to be sure I give the right instructions -td]

### 3.5.11 Other actions

The instructions above describe the simplest way of using git on Windows. Other git facilities which may usefully supplement these include

- Using multiple local branches (Create, Rename, Delete)
- Resetting branches
- Cherry-picking commits
- Pushing commits to remote/origin/master
- Using gitk to review history

Once familiarity with using git on Windows has been gained the standard git manuals can be used to learn about these.

#### LilyPond — Contributor’s Guide