Merge commit 'origin/dev/jneeman' into systems-per-page

[lilypond.git] / Documentation / devel / git-starting.itexi

@c -*- coding: us-ascii; mode: texinfo; -*-
@node Starting with git
@chapter Starting with git

To complete or present in another form the introduction to Git usage
in this chapter, it may be a good idea to look for Git documentation
at @uref{http://git-scm.com/documentation}, 

@menu
* Getting the source code::     
* Updating the source code::    
* Working with several Git branches::  
* Sharing your changes::        
* Other interesting Git commands::  
* Git on Windows::              
@end menu


@node Getting the source code
@section Getting the source code

@menu
* Git introduction::            
* Main source code::            
* Website source code::         
* Documentation translations source code::  
* Other branches::              
* Other locations for git::     
* Git user configuration::      
@end menu

@node Git introduction
@subsection Git introduction

The source code is kept in a Git respository.  This allows us to
track changes to files, and for multiple people to work on the
same set of files efficiently.

@warning{These instructions assume that you are using the
command-line version of Git 1.5 or higher.  Windows users should
skip to @ref{Git on Windows}.}


@node Main source code
@subsection Main source code

To get the main source code and documentation,

@c WARNING: when updating the commands below, please
@c update the other flavors in the two next nodes
@c and in Introduction to Git concepts
@smallexample
mkdir lilypond; cd lilypond
git init-db
git remote add -f -t master -m master origin git://git.sv.gnu.org/lilypond.git/
git checkout -b master origin/master
@end smallexample


@node Website source code
@subsection Website source code

To get the website (including translations),

@smallexample
mkdir lilypond-web ; cd lilypond-web
git init-db
git remote add -f -t web -m web origin git://git.sv.gnu.org/lilypond.git/
git checkout -b web origin/web
@end smallexample


@node Documentation translations source code
@subsection Documentation translations source code

To translate the documentation (@emph{not} the website),

@smallexample
mkdir lilypond-translation; cd lilypond-translation
git init-db
git remote add -f -t lilypond/translation -m lilypond/translation origin git://git.sv.gnu.org/lilypond.git/
git checkout -b lilypond/translation origin/lilypond/translation
@end smallexample


@node Other branches
@subsection Other branches

Most contributors will never need to touch the other branches.  If
you wish to do so, you will need more familiarity with git.

@itemize

@item @code{gub}:
This stores the Grand Unified Binary, our cross-platform building
tool.  
@c TODO: merge the gub stuff with this CG.
For more info, see @uref{http://lilypond.org/gub}.  The git
location is:

@example
http://github.com/janneke/gub
@end example

@item @code{dev/XYZ}:
These branches are for individual developers.  They store code
which is not yet stable enough to be added to the @code{master}
branch.

@item @code{stable/XYZ}:
The branches are kept for archival reasons.

@end itemize


@node Other locations for git
@subsection Other locations for git

If you have difficulty connecting to most of the repositories
listed in earlier sections, try:

@example
http://git.sv.gnu.org/r/lilypond.git
git://git.sv.gnu.org/lilypond.git
ssh://git.sv.gnu.org/srv/git/lilypond.git
@end example

Using HTTP protocol is slowest, so it is not recommended unless both
SSH and Git protocols fail, which happens e.g. if you connect to
internet through a router that filters out Git and/or SSH connections.


@node Git user configuration
@subsection Git user configuration

To configure git to automatically use your name and email address
for commits and patches,

@example
git config --global user.name "MYNAME"
git config --global user.email MYEMAIL@@EXAMPLE.NET
@end example


@node Updating the source code
@section Updating the source code

@menu
* Importance of updating::      
* Update command::              
* Resolving conflicts::         
* Introduction to Git concepts::  
@end menu


@node Importance of updating
@subsection Importance of updating

In a large project like LilyPond, contributors sometimes edit the same
file at the same time.  As long as everybody updates their version of
the file with the most recent changes (@emph{pulling}), there are
generally no problems with this multiple-person editing.  However,
boring problems can arise if you do not pull before attempting commit,
e.g. you may encounter a conflict; in this case, see @ref{Resolving
conflicts}.


@node Update command
@subsection Updating command

Whenever you are asked to pull, it means you should update your
local copy of the repository with the changes made by others on
the remote @code{git.sv.gnu.org} repository:

@example
git pull origin
@end example


@node Resolving conflicts
@subsection Resolving conflicts

Occasionally an update may result in conflicts -- this happens
when you and somebody else have modified the same part of the same
file and git cannot figure out how to merge the two versions
together.  When this happens, you must manually merge the two
versions.

If you need some documentation to understand and resolve conflicts,
see paragraphs @emph{How conflicts are presented} and @emph{How to
resolve conflicts} in @command{git merge} man page.


@node Introduction to Git concepts
@subsection Introduction to Git concepts

A bit of Git vocabulary will be explained below.  The following is
just introduction material; for better understanding of Git concepts,
you are invited to read further documentation, especially Git
Community Book at @uref{http://book.git-scm.com/}.

The @code{git pull origin} command above is just a shortcut for this
command:

@example
git pull git://git.sv.gnu.org/lilypond.git/ @var{branch}:origin/@var{branch}
@end example

@noindent
where @code{@var{branch}} is typically @code{master}, @code{web} or
@code{lilypond/translation}; if you do not know or remember, see
@ref{Getting the source code} to remember which commands you issued or
which source code you wanted to get.

A @emph{commit} is a set of changes made to the sources; it also
includes the committish of the parent commit, the name and e-mail of
the @emph{author} (the person who wrote the changes), the name and
e-mail of the @emph{committer} (the person who brings these changes
into the Git repository), and a commit message.

A @emph{committish} is the SHA1 checksum of a commit, a number made of
40 hexadecimal digits, which acts as the internal unique identifier
for this commit.  To refer to a particular revision, don't use vague
references like the (approximative) date, simply copy and paste the
committish.

A @emph{branch} is nothing more than a pointer to a particular commit,
which is called the @emph{head} of the branch; when referring to a
branch, one often acutally thinks about its head and the ancestor
commits of the head.

Now we will explain the two last commands you used to get the source
code from Git -- see @ref{Getting the source code}.

@example
git remote add -f -t @var{branch} -m @var{branch} origin git://git.sv.gnu.org/lilypond.git/
git checkout -b @var{branch} origin/@var{branch}
@end example

The @command{git remote} has created a branch called
@code{origin/@var{branch}} in your local Git repository.  As this
branch is a copy of the remote branch web from git.sv.gnu.org LilyPond
repository, it is called a @emph{remote branch}, and is meant to track
the changes on the branch from git.sv.gnu.org: it will be updated
every time you run @command{git pull origin} or @command{git fetch
origin}.

The @command{git checkout} command has created a branch named
@code{@var{branch}}.  At the beginning, this branch is identical to
@code{origin/@var{branch}}, but it will differ as soon as you make
changes, e.g. adding newly translated pages or editing some
documentation or code source file.  Whenever you pull, you merge the
changes from @code{origin/@var{branch}} and @code{@var{branch}} since
the last pulling.  If you do not have push (i.e. @qq{write}) access on
git.sv.gnu.org, your @code{@var{branch}} will always differ from
@code{origin/@var{branch}}.  In this case, remember that other people
working like you with the remote branch @code{@var{branch}} of
git://git.sv.gnu.org/lilypond.git/ (called @code{origin/@var{branch}}
on your local repository) know nothing about your own
@code{@var{branch}}: this means that whenever you use a committish or
make a patch, others expect you to take the latest commit of
@code{origin/@var{branch}} as a reference.

Finally, please remember to read the man page of every Git command you
will find in this manual in case you want to discover alternate
methods or just understand how it works.


@node Working with several Git branches
@section Working with several Git branches

It is possible to work with several branches on the same local Git
repository; this is especially useful for translators who may have to
deal with both @code{lilypond/translation} and a stable branch,
e.g. @code{stable/2.12}.

Some Git commands are introduced first, then a workflow with several
Git branches of LilyPond source code is presented.

@menu
* Git commands for managing several branches::  
* Working on LilyPond sources with several branches::  
@end menu

@node Git commands for managing several branches
@subsection Git commands for managing several branches

@subsubheading Listing branches and remotes

You can get the exact path or URL of all remotes with
running

@example
git remote -v
@end example

To list Git branches on your local repositories, run

@example
git branch     # list local branches only
git branch -r  # list remote branches
git branch -a  # list all branches
@end example


@subsubheading Checking out branches

To know the currently checked out branch, i.e. the branch whose source
files are present in your working tree, read the first line of the
output of

@example
git status
@end example

@noindent
The currently checked out branch is also marked with an asterisk in
the output of @command{git branch}.

You can check out another branch @code{@var{other_branch}}, i.e. check
out @code{@var{other_branch}} to the working tree, by running

@example
git checkout @var{other_branch}
@end example

Note that it is possible to check out another branch while having
uncommitted changes, but it is not recommended unless you know what
you are doing; it is recommended to run @command{git status} to check
this kind of issue before checking out another branch.


@subsubheading Merging branches

To merge branch @code{@var{foo}} into branch @code{@var{bar}}, i.e. to
@qq{add} all changes made in branch @code{@var{foo}} to branch
@code{@var{bar}}, run

@example
git checkout @var{bar}
git merge @var{foo}
@end example

If any conflict happens, see @ref{Resolving conflicts}.

There are common usage cases for merging: as a translator, you will
often want to merge @code{master} into @code{lilypond/translation}; on
the other hand, the Translations meister wants to merge
@code{lilypond/translation} into @code{master} whenever he has checked
that @code{lilypond/translation} builds successfully.


@node Working on LilyPond sources with several branches
@subsection Working on LilyPond sources with several branches

@subsubheading Fetching new branches from git.sv.gnu.org

To fetch and check out a new branch named @code{@var{branch}} on
git.sv.gnu.org, run from top of the Git repository

@example
git config --add remote.origin.fetch +refs/heads/@var{branch}:refs/remotes/origin/@var{branch}
git checkout --track -b @var{branch} origin/@var{branch}
@end example

After this, you can pull @code{@var{branch}} from git.sv.gnu.org with

@example
git pull origin
@end example

Note that this command generally fetches all branches you added with
@command{git remote add} (when you initialized the repository) or
@command{git config --add}, i.e. it updates all remote branches from
remote @code{origin}, then it merges the remote branch tracked by
current branch into current branch.  For example, if your current
branch is @code{master} --- which is the case if you got the sources
with the commands described in @ref{Main source code} and did not
issue any @command{git checkout} command --- @code{origin/master} will
be merged into @code{master}.


@subsubheading Local clones, or having several working trees

If you play with several Git branches, e.g. @code{master},
@code{lilypond/translation}, @code{stable/2.12}), you may want to have
one source and build tree for each branch; this is possible with
subdirectories of your local Git repository, used as local cloned
subrepositories.  To create a local clone for the branch named
@code{@var{branch}}, run

@example
git checkout @var{branch}
git clone -l -s -n . @var{subdir}
cd @var{subdir}
git reset --hard
@end example

Note that @code{@var{subdir}} must be a directory name which does not
already exist.  In @code{@var{subdir}}, you can use all Git commands
to browse revisions history, commit and uncommit changes; to update
the cloned subrepository with changes made on the main repository, cd
into @code{@var{subdir}} and run @command{git pull}; to send changes
made on the subrepository back to the main repository, run
@command{git push} from @code{@var{subdir}}.  Note that only one
branch (the currently checked out branch) is created in the
subrepository by default; it is possible to have several branches in a
subrepository and do usual operations (checkout, merge, create,
delete...) on these branches, but this possibility is not detailed
here.

When you push @code{@var{branch}} from @code{@var{subdir}} to the main
repository, and @code{@var{branch}} is checked out in the main
repository, you must save uncommitted changes (see @command{git
stash}) and do @command{git reset --hard} in the main repository in
order to apply pushed changes in the working tree of the main
repository.


@node Sharing your changes
@section Sharing your changes

@menu
* Producing a patch::           
* Committing directly::         
@end menu


@node Producing a patch
@subsection Producing a patch

Once you have finished editing your files, checked that your changes
meet the @ref{Code style}, and/or @ref{Documentation policy}, properly
set up your name and email in @ref{Git user configuration}, and
checked that the entire thing compiles, you may

@example
git commit -a 
git format-patch origin
@end example

Send an email to @email{lilypond-devel@@gnu.org} with the diff as
an attachment.


@node Committing directly
@subsection Committing directly

Most contributors do not have permission to commit directly.  If you
do, make sure you have set up your name and email in @ref{Git user
configuration}, then edit @file{.git/config}: change the line

@example
        url = git://git.sv.gnu.org/lilypond.git/
@end example

@noindent
into
@example
        url = ssh://@var{user}@@git.sv.gnu.org/srv/git/lilypond.git
@end example

@noindent
where @var{user} is your login name on Savannah.

If you have not already done so, you should generate and upload a SSH
key: open @uref{https://savannah.gnu.org/my/} in your browser, then go to
@q{Preferences} then to something like @q{Edit SSH Keys}, and follow
the instructions on that page.

You may then

@example
git push origin
@end example


@node Other interesting Git commands
@section Other interesting Git commands

@menu
* Git log::                     
* Applying git patches::        
@end menu


@node Git log
@subsection Git log

The commands above don't only bring you the latest version of the
sources, but also the full history of revisions (revisons, also
called commits, are changes made to the sources), stored in the
.git directory.  You can browse this history with

@example
git log     # only shows the logs (author, committish and commit message)
git log -p  # also shows diffs
gitk        # shows history graphically
@end example

@warning{The @code{gitk} command may require a separate @code{gitk} package,
available in the appropriate distribution's repositories.}

@node Applying git patches
@subsection Applying git patches

Well-formed git patches should be committed with

@example
git am
@end example

Patches created without @code{git format-patch} should be
committed with

@example
git apply
@end example



@node Git on Windows
@section Git on Windows

@c Some of this may duplicate stuff in other sections
@c Clear this up later  -td

@subsection 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 respository
for LilyPond files.  Editors hold local copies of the master
repository together with any changes they have made locally.  Local
changes are held in a local @q{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 @q{checked out} local branch.

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

@subsection Installing git

Obtain Git from
@uref{http://code.google.com/p/msysgit/downloads/list}.
(Note, not msysGit, which is for Git developers) and
install.

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.

@subsection 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.
You will need to have space for around 150Mbytes.

In the git bash shell type

@example
cd [path]/Git
@end example

to position the shell at your new Git repository.

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

@example
cd "[path]/Git"
@end example

Then type

@example
git init
@end example

to initialize your Git repository.

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

@example
git remote add -f -t master origin git://git.sv.gnu.org/lilypond.git
@end example

to download the lilypond master files.

@warning{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, here we call it @q{lily-local} - you may wish to make up
your own.

Then, finally, type

@example
git checkout -b lily-local origin/master
@end example

to create the lily-local branch containing the local copies of the
master files.  You will be advised your local branch has been set
up to track the remote branch.

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 Git/Documentation/user.

Terminate the Git bash shell by typing @code{exit}.

@subsection 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

@example
cd [path]/Git
git gui
@end example

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 two panels on the left contain the names of files which
you are in the process of editing (Unstaged Changes), and
files you have finished editing and have staged ready for
committing (Staged Changes).  At this stage 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.

The final 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.

@subsection Personalising your local git repository

Open the Git GUI, click on

@example
Edit -> Options
@end example

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

@subsection Checking out a branch

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

@example
Branch -> Checkout
@end example

You should have one local branch called @w{lily-local} and one
tracking branch called @w{origin/master}.  The latter is your
local copy of the @w{remote/origin/master} branch in the master
LilyPond repository.  The @w{lily-local} 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.

@subsection Updating files from @w{remote/origin/master}

Before starting the editing of a file, ensure your local branches
contain the latest version in @w{remote/origin/master} by first
clicking

@example
Remote -> Fetch from -> origin
@end example

@noindent
in the Git GUI.

This will place the latest version of every file, including all the
changes made by others,
into the @q{origin/master} branch of the tracking branches
in your git repository.  You can see these files by checking
out this branch.  This will not affect any files you have
modified in your local branch.

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

@example
Merge -> Local Merge
@end example

@noindent
and if necessary select the local branch into which the merge
is to be made.

Note that a merge cannot be completed if there are any local
uncommitted changes on the lily-local branch.

This will update all the files in that branch to reflect the
current state of the @w{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).

@subsection Editing files

First ensure your lily-local 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 at
editing any time.

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

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 lily-local 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

@example
Commit -> Amend Last Commit
@end example

@noindent
or by checking the Amend Last Commit radio button at bottom left.
This will return the changes to the Staged state, so further
editing made be carried out within that commit.  This must only be
done @emph{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.


@subsection Sending changes to remote/origin/master

If you do not have write access to @w{remote/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

@example
cd [path]/Git
@end example

if necessary, then produce the patch with

@example
git format-patch origin
@end example

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

@subsection Resolving merge conflicts

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

@example
Repository -> Visualise all branch history
@end example

This opens up a very useful new window called @q{gitk}.
Use this to browse all the commits made by others.

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

If a file being merged from @w{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 @w{remote/origin/master}
for you has added some changes of his own before
committing your changes to @w{remote/origin/master}, or if someone
else has changed the same file since you last
fetched the file from @w{remote/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]


@subsection Other actions

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

@itemize

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

@end itemize

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