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=head1 NAME

perlrepository - Using the Perl source repository

=head1 SYNOPSIS

All of Perl's source code is kept centrally in a Git repository. The
repository contains many Perl revisions from Perl 1 onwards and all
the revisions from Perforce, the version control system we were using
previously. This repository is accessible in different ways.

The full repository takes up about 80MB of disk space. A check out of
the blead branch (that is, the master branch, which contains bleadperl,
the development version of perl 5) takes up about 160MB of disk space
(including the repository). A build of bleadperl takes up about 200MB
(including the repository and the check out).

=head1 GETTING ACCESS TO THE REPOSITORY

=head2 READ ACCESS VIA THE WEB

You may access this over the web. This allows you to browse the tree,
see recent commits, search for particular commits and more. You may
access it at:

  http://perl5.git.perl.org/perl.git

=head2 READ ACCESS VIA GIT

You will need a copy of Git for your computer. You can fetch a copy of
the repository using the Git protocol (which uses port 9418):

  git clone git://perl5.git.perl.org/perl.git perl-git

This clones the repository and makes a local copy in the 'perl-git'
directory.

If your local network does not allow you to use port 9418, then you can
fetch a copy of the repository over HTTP (this is slower):

  git clone http://perl5.git.perl.org/perl.git perl-http

This clones the repository and makes a local copy in the 'perl-http'
directory.

=head2 WRITE ACCESS TO THE REPOSITORY

If you are a committer, then you can fetch a copy of the repository that
you can push back on with:

  git clone ssh://perl5.git.perl.org/gitroot/perl.git perl-ssh

This clones the repository and makes a local copy in the 'perl-ssh'
directory.

If you clone using git, which is faster than ssh, then you will need to
modify your config in order to enable pushing. Edit F<.git/config> where
you will see something like:

  [remote "origin"]
  url = git://perl5.git.perl.org/perl.git

change that to something like this:

  [remote "origin"]
  url = ssh://perl5.git.perl.org/gitroot/perl.git

NOTE: there are symlinks set up so that the /gitroot is actually optional.

You can also set up your user name and e-mail address. For example

  % git config user.name "Leon Brocard"
  % git config user.email acme@astray.com

It is also possible to keep C<origin> as a git remote, and add a new remote for ssh access:

  % git remote add camel user@camel:/gitroot/perl.git

This allows you to update your local repository by pulling from C<origin>, which is faster and doesn't require you to authentify, and to push your changes back with the C<camel> remote:

  % git fetch camel
  % git push camel

The C<fetch> command just updates the C<camel> refs, as the objects themselves should have been fetched when pulling from C<origin>.

=head1 OVERVIEW OF THE REPOSITORY

Once you have changed into the repository directory, you can inspect it.


After a clone the repository will contain a single local branch, which
will be the current branch as well, as indicated by the asterix.

  % git branch
  * blead

Using the -a switch to branch will also show the remote tracking branches in the
repository:

  % git branch -a
  * blead
    origin/HEAD
    origin/blead
  ...

The branches that begin with "origin" correspond to the "git remote" that
you cloned from (which is named "origin"). Each branch on the remote will
be exactly tracked by theses branches. You should NEVER do work on these
remote tracking branches. You only ever do work in a local branch. Local
branches can be configured to automerge (on pull) from a designated remote
tracking branch. This is the case with the default branch C<blead> which
will be configured to merge from the remote tracking branch
C<origin/blead>.

You can see recent commits:

  % git log

And pull new changes from the repository, and update your local repository
(must be clean first)

  % git pull

Assuming we are on the branch C<blead> immediately after a pull, this command
would be more or less equivalent to:

  % git fetch
  % git merge origin/blead

In fact if you want to update your local repository without touching your working
directory you do:

  % git fetch

And if you want to update your remote-tracking branches for all defined remotes
simultaneously you can do

  % git remote update

Neither of these last two commands will update your working directory, however
both will update the remote-tracking branches in your repository.

To switch to another branch:

  % git checkout origin/maint-5.8-dor

To switch back to blead:

  % git checkout blead

=head2 FINDING OUT YOUR STATUS

The most common git command you will use will probably be

  % git status

This command will produce as output a description of the current state of the
repository, including modified files and unignored untracked files, and in addition
it will show things like what files have been staged for the next commit,
and usually some useful information about how to change things. For instance the
following:

  $ git status
  # On branch blead
  # Your branch is ahead of 'origin/blead' by 1 commit.
  #
  # Changes to be committed:
  #   (use "git reset HEAD <file>..." to unstage)
  #
  #       modified:   pod/perlrepository.pod
  #
  # Changed but not updated:
  #   (use "git add <file>..." to update what will be committed)
  #
  #       modified:   pod/perlrepository.pod
  #
  # Untracked files:
  #   (use "git add <file>..." to include in what will be committed)
  #
  #       deliberate.untracked

This shows that there were changes to this document staged for commit, and
that there were further changes in the working directory not yet staged. It
also shows that there was an untracked file in the working directory, and as
you can see shows how to change all of this. It also shows that there
is one commit on the  working branch C<blead> which has not been pushed to the
C<origin> remote yet. B<NOTE>: that this output is also what you see as a
template if you do not provide a message to C<git commit>.

Assuming we commit all the mentioned changes above:

  % git commit -a -m'explain git status and stuff about remotes'
  Created commit daf8e63: explain git status and stuff about remotes
   1 files changed, 83 insertions(+), 3 deletions(-)

We can re-run git status and see something like this:

  % git status
  # On branch blead
  # Your branch is ahead of 'origin/blead' by 2 commits.
  #
  # Untracked files:
  #   (use "git add <file>..." to include in what will be committed)
  #
  #       deliberate.untracked
  nothing added to commit but untracked files present (use "git add" to track)


When in doubt, before you do anything else, check your status and read it
carefully, many questions are answered directly by the git status output.

=head1 SUBMITTING A PATCH

If you have a patch in mind for Perl, you should first get a copy of
the repository:

  % git clone git://perl5.git.perl.org/perl.git perl-git

Then change into the directory:

  % cd perl-git

Alternatively, if you already have a Perl repository, you should
ensure that you're on the I<blead> branch, and your repository
is up to date:

  % git checkout blead
  % git pull

Now that we have everything up to date, we need to create a temporary new
branch for these changes and switch into it:

  % git checkout -b orange

which is the short form of

  % git branch orange
  % git checkout orange

Then make your changes. For example, if Leon Brocard changes his name
to Orange Brocard, we should change his name in the AUTHORS file:

  % perl -pi -e 's{Leon Brocard}{Orange Brocard}' AUTHORS

You can see what files are changed:

  % git status
  # On branch blead
  # Changes to be committed:
  #   (use "git reset HEAD <file>..." to unstage)
  #
  #	modified:   AUTHORS
  #

And you can see the changes:

  % git diff
  diff --git a/AUTHORS b/AUTHORS
  index 293dd70..722c93e 100644
  --- a/AUTHORS
  +++ b/AUTHORS
  @@ -541,7 +541,7 @@    Lars Hecking                   <lhecking@nmrc.ucc.ie>
   Laszlo Molnar                  <laszlo.molnar@eth.ericsson.se>
   Leif Huhn                      <leif@hale.dkstat.com>
   Len Johnson                    <lenjay@ibm.net>
  -Leon Brocard                   <acme@astray.com>
  +Orange Brocard                 <acme@astray.com>
   Les Peters                     <lpeters@aol.net>
   Lesley Binks                   <lesley.binks@gmail.com>
   Lincoln D. Stein               <lstein@cshl.org>

Now commit your change locally:

  % git add AUTHORS
  % git commit -m 'Rename Leon Brocard to Orange Brocard'
  Created commit 6196c1d: Rename Leon Brocard to Orange Brocard
   1 files changed, 1 insertions(+), 1 deletions(-)

Now you should create a patch file for all your local changes:

  % git format-patch origin
  0001-Rename-Leon-Brocard-to-Orange-Brocard.patch

You should now send an email to perl5-porters@perl.org with a
description of your changes, and attach this patch file as an
attachment.

If you want to delete your temporary branch, you may do so with:

  % git checkout blead
  % git branch -d orange
  error: The branch 'orange' is not an ancestor of your current HEAD.
  If you are sure you want to delete it, run 'git branch -D orange'.
  % git branch -D orange
  Deleted branch orange.

=head1 ACCEPTING A PATCH

If you have received a patch file generated using the above section,
you should try out the patch.

First we need to create a temporary new branch for these changes and
switch into it:

  % git checkout -b experimental

Patches that were formatted by C<git format-patch> are applied with C<git am>:

  % git am 0001-Rename-Leon-Brocard-to-Orange-Brocard.patch
  Applying Rename Leon Brocard to Orange Brocard

If just a raw diff is provided, it is also possible use this two-step process:

  % git apply bugfix.diff
  % git commit -am "Some fixing" --author="That Guy <that.guy@internets.com>"

Now we can inspect the change:

  % git log
  commit b1b3dab48344cff6de4087efca3dbd63548ab5e2
  Author: Leon Brocard <acme@astray.com>
  Date:   Fri Dec 19 17:02:59 2008 +0000

    Rename Leon Brocard to Orange Brocard
  ...

  % git diff blead
  diff --git a/AUTHORS b/AUTHORS
  index 293dd70..722c93e 100644
  --- a/AUTHORS
  +++ b/AUTHORS
  @@ -541,7 +541,7 @@ Lars Hecking                        <lhecking@nmrc.ucc.ie>
   Laszlo Molnar                  <laszlo.molnar@eth.ericsson.se>
   Leif Huhn                      <leif@hale.dkstat.com>
   Len Johnson                    <lenjay@ibm.net>
  -Leon Brocard                   <acme@astray.com>
  +Orange Brocard                 <acme@astray.com>
   Les Peters                     <lpeters@aol.net>
   Lesley Binks                   <lesley.binks@gmail.com>
   Lincoln D. Stein               <lstein@cshl.org>

If you are a committer to Perl and you think the patch is good, you can
then merge it into blead then push it out to the main repository:

  % git checkout blead
  % git merge experimental
  % git push

If you want to delete your temporary branch, you may do so with:

  % git checkout blead
  % git branch -d experimental
  error: The branch 'experimental' is not an ancestor of your current HEAD.
  If you are sure you want to delete it, run 'git branch -D experimental'.
  % git branch -D experimental
  Deleted branch experimental.

=head1 CLEANING A WORKING DIRECTORY

The command C<git clean> can with varying arguments be used as a replacement for make-clean.

To reset your working directory to a pristine condition you can do:

  git clean -dxf

However, be aware this will delete ALL untracked content. You can use

  git clean -Xf

to remove all ignored untracked files, such as build and test byproduct, but leave any 
manually created files alone.

=head1 BISECTING

C<git> provides a built-in way to determine, with a binary search in the history, which commit should be blamed for introducing a given bug.

Suppose that we have a script F<~/testcase.pl> that exits with C<0> when some behaviour is correct, and with C<1> when it's faulty. We need an helper script that automates building C<perl> and running the testcase:

  % cat ~/run
  #!/bin/sh
  git clean -dxf
  # If you can use ccache, add -Dcc=ccache\ gcc -Dld=gcc to the Configure line
  sh Configure -des -Dusedevel -Doptimize="-g" || exit 125
  make || exit 125
  ./perl -Ilib ~/testcase.pl

This script may return C<125> to indicate that the corresponding commit should be skipped. Otherwise, it returns the status of F<~/testcase.pl>.

We first enter in bisect mode with:

  % git bisect start

For example, if the bug is present on C<HEAD> but wasn't in 5.10.0, C<git> will learn about this when you enter:

  % git bisect bad
  % git bisect good perl-5.10.0
  Bisecting: 853 revisions left to test after this

This results in checking out the median commit between C<HEAD> and C<perl-5.10.0>. We can then run the bisecting process with:

  % git bisect run ~/run

When the first bad commit is isolated, C<git bisect> will tell you so:

  ca4cfd28534303b82a216cfe83a1c80cbc3b9dc5 is first bad commit
  commit ca4cfd28534303b82a216cfe83a1c80cbc3b9dc5
  Author: Dave Mitchell <davem@fdisolutions.com>
  Date:   Sat Feb 9 14:56:23 2008 +0000

      [perl #49472] Attributes + Unkown Error
      ...

  bisect run success

You can peek into the bisecting process with C<git bisect log> and C<git bisect visualize>. C<git bisect reset> will get you out of bisect mode.

Please note that the first C<good> state must be an ancestor of the first C<bad> state. If you want to search for the commit that I<solved> some bug, you have to negate your test case (i.e. exit with C<1> if OK and C<0> if not) and still mark the lower bound as C<good> and the upper as C<bad>. The "first bad commit" has then to be understood as the "first commit where the bug is solved".

C<git help bisect> has much more information on how you can tweak your binary searches.

=head1 COMITTING TO MAINTENANCE VERSIONS

To commit to a maintenance version of perl, you need to create a local
tracking branch:

  % git checkout --track -b maint-5.005 origin/maint-5.005

This creates a local branch named maint-5.005, which tracks the remote
branch origin/maint-5.005. Then you can pull, commit, merge and push
as before.