refine the documentation for deleting branches and altering history

[perl5.git] / pod / perlrepository.pod

=for comment
Consistent formatting of this file is achieved with:
  perl ./Porting/podtidy pod/perlrepository.pod

=head1 NAME

perlrepository - Using the Perl source repository

=head1 SYNOPSIS

All of Perl's source code is kept centrally in a Git repository at
I<perl5.git.perl.org>. 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 main development 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 the repository over the web. This allows you to browse
the tree, see recent commits, subscribe to RSS feeds for the changes,
search for particular commits and more. You may access it at:

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

A mirror of the repository is found at:

  http://github.com/github/perl

=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 F<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 F<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 F<perl-ssh>
directory.

If you cloned using the git protocol, 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 optional and
since SSH is the default protocol you can actually shorten the "url" to
C<perl5.git.perl.org:/perl.git>.

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

This allows you to update your local repository by pulling from
C<origin>, which is faster and doesn't require you to authenticate, 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>.

The committers have access to 2 servers that serve perl5.git.perl.org.
One is camel.booking.com, which is the 'master' repository. The
perl5.git.perl.org IP address also lives on this machine. The second
one is dromedary.booking.com, which can be used for general testing and
development. Dromedary syncs the git tree from camel every few minutes,
you should not push there. Both machines also have a full CPAN mirror.
To share files with the general public, dromedary serves your
~/public_html/ as http://users.perl5.git.perl.org/~yourlogin/

=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 asterisk.

  % git branch
  * blead

Using the -a switch to C<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 make a local branch of a remote branch:

  % git checkout -b maint-5.10 origin/maint-5.10

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

It's preferable to patch against the latest blead version, since this
is where new development occurs for all changes other than critical bug
fixes.  Critical bug fix patches should be made against the relevant
maint branches, or should be submitted with a note indicating all the
branches where the fix should be applied.

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 orange
  # 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 commit -a -m 'Rename Leon Brocard to Orange Brocard'
  Created commit 6196c1d: Rename Leon Brocard to Orange Brocard
   1 files changed, 1 insertions(+), 1 deletions(-)

You can examine your last commit with:

  % git show HEAD

and if you are not happy with either the description or the patch
itself you can fix it up by editing the files once more and then issue:

  % git commit -a --amend

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 include this patch file as an
attachment.  (See the next section for how to configure and use
git to send these emails for you.)

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.

=head2 Using git to send patch emails

In your ~/git/perl repository, set the destination email to the perl5-porters
mailing list.

  $ git config sendemail.to perl5-porters@perl.org

Then you can use git directly to send your patch emails:

  $ git send-email 0001-Rename-Leon-Brocard-to-Orange-Brocard.patch

You may need to set some configuration variables for your particular email
service provider. For example, to set your global git config to send email via
a gmail account:

  $ git config --global sendemail.smtpserver smtp.gmail.com
  $ git config --global sendemail.smtpssl 1
  $ git config --global sendemail.smtpuser YOURUSERNAME@gmail.com

With this configuration, you will be prompted for your gmail password when you
run 'git send-email'.  You can also configure C<sendemail.smtppass> with your
password if you don't care about having your password in the .gitconfig file.

=head2 A note on derived files

Be aware that many files in the distribution are derivative--avoid
patching them, because git won't see the changes to them, and the build
process will overwrite them. Patch the originals instead.  Most
utilities (like perldoc) are in this category, i.e. patch
utils/perldoc.PL rather than utils/perldoc. Similarly, don't create
patches for files under $src_root/ext from their copies found in
$install_root/lib.  If you are unsure about the proper location of a
file that may have gotten copied while building the source
distribution, consult the C<MANIFEST>.

=for XXX

What should we recommend about binary files now? Do we need anything?

=head2 Getting your patch accepted

The first thing you should include with your patch is a description of
the problem that the patch corrects.  If it is a code patch (rather
than a documentation patch) you should also include a small test case
that illustrates the bug (a patch to an existing test file is
preferred).

If you are submitting a code patch there are several other things that
you need to do.

=over 4

=item Comments, Comments, Comments

Be sure to adequately comment your code.  While commenting every line
is unnecessary, anything that takes advantage of side effects of
operators, that creates changes that will be felt outside of the
function being patched, or that others may find confusing should be
documented.  If you are going to err, it is better to err on the side
of adding too many comments than too few.

=item Style

In general, please follow the particular style of the code you are
patching.

In particular, follow these general guidelines for patching Perl
sources:

    8-wide tabs (no exceptions!)
    4-wide indents for code, 2-wide indents for nested CPP #defines
    try hard not to exceed 79-columns
    ANSI C prototypes
    uncuddled elses and "K&R" style for indenting control constructs
    no C++ style (//) comments
    mark places that need to be revisited with XXX (and revisit often!)
    opening brace lines up with "if" when conditional spans multiple
        lines; should be at end-of-line otherwise
    in function definitions, name starts in column 0 (return value is on
        previous line)
    single space after keywords that are followed by parens, no space
        between function name and following paren
    avoid assignments in conditionals, but if they're unavoidable, use
        extra paren, e.g. "if (a && (b = c)) ..."
    "return foo;" rather than "return(foo);"
    "if (!foo) ..." rather than "if (foo == FALSE) ..." etc.

=item Testsuite

When submitting a patch you should make every effort to also include an
addition to perl's regression tests to properly exercise your patch.
Your testsuite additions should generally follow these guidelines
(courtesy of Gurusamy Sarathy <gsar@activestate.com>):

    Know what you're testing.  Read the docs, and the source.
    Tend to fail, not succeed.
    Interpret results strictly.
    Use unrelated features (this will flush out bizarre interactions).
    Use non-standard idioms (otherwise you are not testing TIMTOWTDI).
    Avoid using hardcoded test numbers whenever possible (the
      EXPECTED/GOT found in t/op/tie.t is much more maintainable,
      and gives better failure reports).
    Give meaningful error messages when a test fails.
    Avoid using qx// and system() unless you are testing for them.  If you
      do use them, make sure that you cover _all_ perl platforms.
    Unlink any temporary files you create.
    Promote unforeseen warnings to errors with $SIG{__WARN__}.
    Be sure to use the libraries and modules shipped with the version
      being tested, not those that were already installed.
    Add comments to the code explaining what you are testing for.
    Make updating the '1..42' string unnecessary.  Or make sure that
      you update it.
    Test _all_ behaviors of a given operator, library, or function:
      - All optional arguments
      - Return values in various contexts (boolean, scalar, list, lvalue)
      - Use both global and lexical variables
      - Don't forget the exceptional, pathological cases.

=back

=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 -a -m "Some fixing" --author="That Guy <that.guy@internets.com>"

Now we can inspect the change:

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

    Rename Leon Brocard to Orange Brocard

  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 C<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.

If you only want to cancel some uncommitted edits, you can use C<git
checkout> and give it a list of files to be reverted, or C<git checkout
-f> to revert them all.

If you want to cancel one or several commits, you can use C<git reset>.

=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"
  test -f config.sh || exit 125
  # Correct makefile for newer GNU gcc
  perl -ni -we 'print unless /<(?:built-in|command)/' makefile x2p/makefile
  # if you just need miniperl, replace test_prep with miniperl
  make -j4 test_prep
  [ -x ./perl ] || exit 125
  ./perl -Ilib ~/testcase.pl
  ret=$?
  [ $ret -gt 127 ] && ret=127
  git clean -dxf
  exit $ret

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 + Unknown 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 SUBMITTING A PATCH VIA GITHUB

GitHub is a website that makes it easy to fork and publish projects
with Git. First you should set up a GitHub account and log in.

Perl's git repository is mirrored on GitHub at this page:

  http://github.com/github/perl/tree/blead

Visit the page and click the "fork" button. This clones the Perl git
repository for you and provides you with "Your Clone URL" from which
you should clone:

  % git clone git@github.com:USERNAME/perl.git perl-github

We shall make the same patch as above, creating a new branch:

  % cd perl-github
  % git remote add upstream git://github.com/github/perl.git
  % git pull upstream blead
  % git checkout -b orange
  % perl -pi -e 's{Leon Brocard}{Orange Brocard}' AUTHORS
  % git commit -a -m 'Rename Leon Brocard to Orange Brocard'
  % git push origin orange

The orange branch has been pushed to GitHub, so you should now send an
email to perl5-porters@perl.org with a description of your changes and
the following information:

  http://github.com/USERNAME/perl/tree/orange
  git@github.com:USERNAME/perl.git branch orange

=head1 MERGING FROM A BRANCH VIA GITHUB

If someone has provided a branch via GitHub and you are a committer,
you should use the following in your perl-ssh directory:

  % git remote add dandv git://github.com/dandv/perl.git
  % git fetch

Now you can see the differences between the branch and blead:

  % git diff dandv/blead

And you can see the commits:

  % git log dandv/blead

If you approve of a specific commit, you can cherry pick it:

  % git cherry-pick 3adac458cb1c1d41af47fc66e67b49c8dec2323f

Or you could just merge the whole branch if you like it all:

  % git merge dandv/blead

And then push back to the repository:

  % git push


=head1 TOPIC BRANCHES AND REWRITING HISTORY

Individual committers should create topic branches under
B<yourname>/B<some_descriptive_name>. Other committers should check with
a topic branch's creator before making any change to it.

If you are not the creator of B<yourname>/B<some_descriptive_name>, you
might sometimes find that the original author has edited the branch's
history. There are lots of good reasons for this. Sometimes, an author
might simply be rebasing the branch onto a newer source point. Sometimes,
an author might have found an error in an early commit which they wanted
to fix before merging the branch to blead.

Currently the master repository is configured to forbid non-fast-forward
merges.  This means that the branches within can not be rebased and
pushed as a single step.

The only way you will ever be allowed to rebase or modify the history of
a pushed branch is to delete it and push it as a new branch under the same
name. Please think carefully about doing this. It may be better to sequentially
rename your branches so that it is easier for others working with you to
cherry-pick their local changes onto the new version. (XXX: needs
explanation).

If you want to rebase a personal topic branch, you will have to delete
your existing topic branch and push as a new version of it. You can do
this via the following formula (see the explanation about C<refspec>'s
in the git push documentation for details) after you have rebased your
branch:

   # first rebase
   $ git checkout $user/$topic
   $ git fetch
   $ git rebase origin/blead

   # then "delete-and-push"
   $ git push origin :$user/$topic
   $ git push origin $user/$topic

B<NOTE:> it is forbidden at the repository level to delete any of the
"primary" branches. That is any branch matching C<m!^(blead|maint|perl)!>.
Any attempt to do so will result in git producing an error like this:

    $ git push origin :blead
    *** It is forbidden to delete blead/maint branches in this repository
    error: hooks/update exited with error code 1
    error: hook declined to update refs/heads/blead
    To ssh://camel.booking.com/perl
     ! [remote rejected] blead (hook declined)
     error: failed to push some refs to 'ssh://camel.booking.com/perl'

As a matter of policy we do B<not> edit the history of the blead and maint-*
branches. If a typo (or worse) sneaks into a commit to blead or maint-*, we'll
fix it in another commit. The only types of updates allowed on these
branches are "fast-forward's", where all history is preserved.

Annotated tags in the canonical perl.git repository will never be deleted
or modified. Think long and hard about whether you want to push a local
tag to perl.git before doing so. (Pushing unannotated tags is
not allowed.)

=head1 COMMITTING TO MAINTENANCE VERSIONS

Maintenance versions should only be altered to add critical bug fixes.

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 C<maint-5.005>, which tracks the
remote branch C<origin/maint-5.005>. Then you can pull, commit, merge
and push as before.

You can also cherry-pick commits from blead and another branch, by
using the C<git cherry-pick> command. It is recommended to use the
B<-x> option to C<git cherry-pick> in order to record the SHA1 of the
original commit in the new commit message.

=head1 GRAFTS

The perl history contains one mistake which was not caught in the
conversion -- a merge was recorded in the history between blead and
maint-5.10 where no merge actually occurred.  Due to the nature of
git, this is now impossible to fix in the public repository.  You can
remove this mis-merge locally by adding the following line to your
C<.git/info/grafts> file:

  296f12bbbbaa06de9be9d09d3dcf8f4528898a49 434946e0cb7a32589ed92d18008aaa1d88515930

It is particularly important to have this graft line if any bisecting
is done in the area of the "merge" in question.

=head1 SEE ALSO

The git documentation, accessible via C<git help command>.