1=encoding utf8
2
3=for comment
4Consistent formatting of this file is achieved with:
5  perl ./Porting/podtidy pod/perlgit.pod
6
7=head1 NAME
8
9perlgit - Detailed information about git and the Perl repository
10
11=head1 DESCRIPTION
12
13This document provides details on using git to develop Perl. If you are
14just interested in working on a quick patch, see L<perlhack> first.
15This document is intended for people who are regular contributors to
16Perl, including those with write access to the git repository.
17
18=head1 CLONING THE REPOSITORY
19
20All of Perl's source code is kept centrally in a Git repository at
21I<github.com>.
22
23You can make a read-only clone of the repository by running:
24
25  % git clone git://github.com/Perl/perl5.git perl
26
27This uses the git protocol (port 9418).
28
29If you cannot use the git protocol for firewall reasons, you can also
30clone via http:
31
32  % git clone https://github.com/Perl/perl5.git perl
33
34=head1 WORKING WITH THE REPOSITORY
35
36Once you have changed into the repository directory, you can inspect
37it. After a clone the repository will contain a single local branch,
38which will be the current branch as well, as indicated by the asterisk.
39
40  % git branch
41  * blead
42
43Using the -a switch to C<branch> will also show the remote tracking
44branches in the repository:
45
46  % git branch -a
47  * blead
48    origin/HEAD
49    origin/blead
50  ...
51
52The branches that begin with "origin" correspond to the "git remote"
53that you cloned from (which is named "origin"). Each branch on the
54remote will be exactly tracked by these branches. You should NEVER do
55work on these remote tracking branches. You only ever do work in a
56local branch. Local branches can be configured to automerge (on pull)
57from a designated remote tracking branch. This is the case with the
58default branch C<blead> which will be configured to merge from the
59remote tracking branch C<origin/blead>.
60
61You can see recent commits:
62
63  % git log
64
65And pull new changes from the repository, and update your local
66repository (must be clean first)
67
68  % git pull
69
70Assuming we are on the branch C<blead> immediately after a pull, this
71command would be more or less equivalent to:
72
73  % git fetch
74  % git merge origin/blead
75
76In fact if you want to update your local repository without touching
77your working directory you do:
78
79  % git fetch
80
81And if you want to update your remote-tracking branches for all defined
82remotes simultaneously you can do
83
84  % git remote update
85
86Neither of these last two commands will update your working directory,
87however both will update the remote-tracking branches in your
88repository.
89
90To make a local branch of a remote branch:
91
92  % git checkout -b maint-5.10 origin/maint-5.10
93
94To switch back to blead:
95
96  % git checkout blead
97
98=head2 Finding out your status
99
100The most common git command you will use will probably be
101
102  % git status
103
104This command will produce as output a description of the current state
105of the repository, including modified files and unignored untracked
106files, and in addition it will show things like what files have been
107staged for the next commit, and usually some useful information about
108how to change things. For instance the following:
109
110 % git status
111 On branch blead
112 Your branch is ahead of 'origin/blead' by 1 commit.
113
114 Changes to be committed:
115   (use "git reset HEAD <file>..." to unstage)
116
117       modified:   pod/perlgit.pod
118
119 Changes not staged for commit:
120   (use "git add <file>..." to update what will be committed)
121   (use "git checkout -- <file>..." to discard changes in working
122                                                              directory)
123
124       modified:   pod/perlgit.pod
125
126 Untracked files:
127   (use "git add <file>..." to include in what will be committed)
128
129       deliberate.untracked
130
131This shows that there were changes to this document staged for commit,
132and that there were further changes in the working directory not yet
133staged. It also shows that there was an untracked file in the working
134directory, and as you can see shows how to change all of this. It also
135shows that there is one commit on the working branch C<blead> which has
136not been pushed to the C<origin> remote yet. B<NOTE>: This output
137is also what you see as a template if you do not provide a message to
138C<git commit>.
139
140=head2 Patch workflow
141
142First, please read L<perlhack> for details on hacking the Perl core.
143That document covers many details on how to create a good patch.
144
145If you already have a Perl repository, you should ensure that you're on
146the I<blead> branch, and your repository is up to date:
147
148  % git checkout blead
149  % git pull
150
151It's preferable to patch against the latest blead version, since this
152is where new development occurs for all changes other than critical bug
153fixes. Critical bug fix patches should be made against the relevant
154maint branches, or should be submitted with a note indicating all the
155branches where the fix should be applied.
156
157Now that we have everything up to date, we need to create a temporary
158new branch for these changes and switch into it:
159
160  % git checkout -b orange
161
162which is the short form of
163
164  % git branch orange
165  % git checkout orange
166
167Creating a topic branch makes it easier for the maintainers to rebase
168or merge back into the master blead for a more linear history. If you
169don't work on a topic branch the maintainer has to manually cherry pick
170your changes onto blead before they can be applied.
171
172That'll get you scolded on perl5-porters, so don't do that. Be Awesome.
173
174Then make your changes. For example, if Leon Brocard changes his name
175to Orange Brocard, we should change his name in the AUTHORS file:
176
177  % perl -pi -e 's{Leon Brocard}{Orange Brocard}' AUTHORS
178
179You can see what files are changed:
180
181  % git status
182  On branch orange
183  Changes to be committed:
184    (use "git reset HEAD <file>..." to unstage)
185
186     modified:   AUTHORS
187
188And you can see the changes:
189
190 % git diff
191 diff --git a/AUTHORS b/AUTHORS
192 index 293dd70..722c93e 100644
193 --- a/AUTHORS
194 +++ b/AUTHORS
195 @@ -541,7 +541,7 @@    Lars Hecking              <lhecking@nmrc.ucc.ie>
196  Laszlo Molnar                  <laszlo.molnar@eth.ericsson.se>
197  Leif Huhn                      <leif@hale.dkstat.com>
198  Len Johnson                    <lenjay@ibm.net>
199 -Leon Brocard                   <acme@astray.com>
200 +Orange Brocard                 <acme@astray.com>
201  Les Peters                     <lpeters@aol.net>
202  Lesley Binks                   <lesley.binks@gmail.com>
203  Lincoln D. Stein               <lstein@cshl.org>
204
205Now commit your change locally:
206
207 % git commit -a -m 'Rename Leon Brocard to Orange Brocard'
208 Created commit 6196c1d: Rename Leon Brocard to Orange Brocard
209  1 files changed, 1 insertions(+), 1 deletions(-)
210
211The C<-a> option is used to include all files that git tracks that you
212have changed. If at this time, you only want to commit some of the
213files you have worked on, you can omit the C<-a> and use the command
214C<S<git add I<FILE ...>>> before doing the commit. C<S<git add
215--interactive>> allows you to even just commit portions of files
216instead of all the changes in them.
217
218The C<-m> option is used to specify the commit message. If you omit it,
219git will open a text editor for you to compose the message
220interactively. This is useful when the changes are more complex than
221the sample given here, and, depending on the editor, to know that the
222first line of the commit message doesn't exceed the 50 character legal
223maximum. See L<perlhack/Commit message> for more information about what
224makes a good commit message.
225
226Once you've finished writing your commit message and exited your
227editor, git will write your change to disk and tell you something like
228this:
229
230 Created commit daf8e63: explain git status and stuff about remotes
231  1 files changed, 83 insertions(+), 3 deletions(-)
232
233If you re-run C<git status>, you should see something like this:
234
235 % git status
236 On branch orange
237 Untracked files:
238   (use "git add <file>..." to include in what will be committed)
239
240       deliberate.untracked
241
242 nothing added to commit but untracked files present (use "git add" to
243                                                                  track)
244
245When in doubt, before you do anything else, check your status and read
246it carefully, many questions are answered directly by the git status
247output.
248
249You can examine your last commit with:
250
251  % git show HEAD
252
253and if you are not happy with either the description or the patch
254itself you can fix it up by editing the files once more and then issue:
255
256  % git commit -a --amend
257
258Now, create a fork on GitHub to push your branch to, and add it as a
259remote if you haven't already, as described in the GitHub documentation
260at L<https://help.github.com/en/articles/working-with-forks>:
261
262  % git remote add fork git@github.com:MyUser/perl5.git
263
264And push the branch to your fork:
265
266  % git push -u fork orange
267
268You should now submit a Pull Request (PR) on GitHub from the new branch
269to blead. For more information, see the GitHub documentation at
270L<https://help.github.com/en/articles/creating-a-pull-request-from-a-fork>.
271
272You can also send patch files to
273L<perl5-porters@perl.org|mailto:perl5-porters@perl.org> directly if the
274patch is not ready to be applied, but intended for discussion.
275
276To create a patch file for all your local changes:
277
278  % git format-patch -M blead..
279  0001-Rename-Leon-Brocard-to-Orange-Brocard.patch
280
281Or for a lot of changes, e.g. from a topic branch:
282
283  % git format-patch --stdout -M blead.. > topic-branch-changes.patch
284
285If you want to delete your temporary branch, you may do so with:
286
287 % git checkout blead
288 % git branch -d orange
289 error: The branch 'orange' is not an ancestor of your current HEAD.
290 If you are sure you want to delete it, run 'git branch -D orange'.
291 % git branch -D orange
292 Deleted branch orange.
293
294=head2 A note on derived files
295
296Be aware that many files in the distribution are derivative--avoid
297patching them, because git won't see the changes to them, and the build
298process will overwrite them. Patch the originals instead. Most
299utilities (like perldoc) are in this category, i.e. patch
300F<utils/perldoc.PL> rather than F<utils/perldoc>. Similarly, don't
301create patches for files under F<$src_root/ext> from their copies found
302in F<$install_root/lib>. If you are unsure about the proper location of
303a file that may have gotten copied while building the source
304distribution, consult the F<MANIFEST>.
305
306=head2 Cleaning a working directory
307
308The command C<git clean> can with varying arguments be used as a
309replacement for C<make clean>.
310
311To reset your working directory to a pristine condition you can do:
312
313  % git clean -dxf
314
315However, be aware this will delete ALL untracked content. You can use
316
317  % git clean -Xf
318
319to remove all ignored untracked files, such as build and test
320byproduct, but leave any manually created files alone.
321
322If you only want to cancel some uncommitted edits, you can use C<git
323checkout> and give it a list of files to be reverted, or C<git checkout
324-f> to revert them all.
325
326If you want to cancel one or several commits, you can use C<git reset>.
327
328=head2 Bisecting
329
330C<git> provides a built-in way to determine which commit should be blamed
331for introducing a given bug. C<git bisect> performs a binary search of
332history to locate the first failing commit. It is fast, powerful and
333flexible, but requires some setup and to automate the process an auxiliary
334shell script is needed.
335
336The core provides a wrapper program, F<Porting/bisect.pl>, which attempts to
337simplify as much as possible, making bisecting as simple as running a Perl
338one-liner. For example, if you want to know when this became an error:
339
340    perl -e 'my $a := 2'
341
342you simply run this:
343
344    .../Porting/bisect.pl -e 'my $a := 2;'
345
346Using F<Porting/bisect.pl>, with one command (and no other files) it's easy to
347find out
348
349=over 4
350
351=item *
352
353Which commit caused this example code to break?
354
355=item *
356
357Which commit caused this example code to start working?
358
359=item *
360
361Which commit added the first file to match this regex?
362
363=item *
364
365Which commit removed the last file to match this regex?
366
367=back
368
369usually without needing to know which versions of perl to use as start and
370end revisions, as F<Porting/bisect.pl> automatically searches to find the
371earliest stable version for which the test case passes. Run
372C<Porting/bisect.pl --help> for the full documentation, including how to
373set the C<Configure> and build time options.
374
375If you require more flexibility than F<Porting/bisect.pl> has to offer, you'll
376need to run C<git bisect> yourself. It's most useful to use C<git bisect run>
377to automate the building and testing of perl revisions. For this you'll need
378a shell script for C<git> to call to test a particular revision. An example
379script is F<Porting/bisect-example.sh>, which you should copy B<outside> of
380the repository, as the bisect process will reset the state to a clean checkout
381as it runs. The instructions below assume that you copied it as F<~/run> and
382then edited it as appropriate.
383
384You first enter in bisect mode with:
385
386  % git bisect start
387
388For example, if the bug is present on C<HEAD> but wasn't in 5.10.0,
389C<git> will learn about this when you enter:
390
391  % git bisect bad
392  % git bisect good perl-5.10.0
393  Bisecting: 853 revisions left to test after this
394
395This results in checking out the median commit between C<HEAD> and
396C<perl-5.10.0>. You can then run the bisecting process with:
397
398  % git bisect run ~/run
399
400When the first bad commit is isolated, C<git bisect> will tell you so:
401
402  ca4cfd28534303b82a216cfe83a1c80cbc3b9dc5 is first bad commit
403  commit ca4cfd28534303b82a216cfe83a1c80cbc3b9dc5
404  Author: Dave Mitchell <davem@fdisolutions.com>
405  Date:   Sat Feb 9 14:56:23 2008 +0000
406
407      [perl #49472] Attributes + Unknown Error
408      ...
409
410  bisect run success
411
412You can peek into the bisecting process with C<git bisect log> and
413C<git bisect visualize>. C<git bisect reset> will get you out of bisect
414mode.
415
416Please note that the first C<good> state must be an ancestor of the
417first C<bad> state. If you want to search for the commit that I<solved>
418some bug, you have to negate your test case (i.e. exit with C<1> if OK
419and C<0> if not) and still mark the lower bound as C<good> and the
420upper as C<bad>. The "first bad commit" has then to be understood as
421the "first commit where the bug is solved".
422
423C<git help bisect> has much more information on how you can tweak your
424binary searches.
425
426Following bisection you may wish to configure, build and test perl at
427commits identified by the bisection process.  Sometimes, particularly
428with older perls, C<make> may fail during this process.  In this case
429you may be able to patch the source code at the older commit point.  To
430do so, please follow the suggestions provided in
431L<perlhack/Building perl at older commits>.
432
433=head2 Topic branches and rewriting history
434
435Individual committers should create topic branches under
436B<yourname>/B<some_descriptive_name>:
437
438  % branch="$yourname/$some_descriptive_name"
439  % git checkout -b $branch
440  ... do local edits, commits etc ...
441  % git push origin -u $branch
442
443Should you be stuck with an ancient version of git (prior to 1.7), then
444C<git push> will not have the C<-u> switch, and you have to replace the
445last step with the following sequence:
446
447  % git push origin $branch:refs/heads/$branch
448  % git config branch.$branch.remote origin
449  % git config branch.$branch.merge refs/heads/$branch
450
451If you want to make changes to someone else's topic branch, you should
452check with its creator before making any change to it.
453
454You
455might sometimes find that the original author has edited the branch's
456history. There are lots of good reasons for this. Sometimes, an author
457might simply be rebasing the branch onto a newer source point.
458Sometimes, an author might have found an error in an early commit which
459they wanted to fix before merging the branch to blead.
460
461Currently the master repository is configured to forbid
462non-fast-forward merges. This means that the branches within can not be
463rebased and pushed as a single step.
464
465The only way you will ever be allowed to rebase or modify the history
466of a pushed branch is to delete it and push it as a new branch under
467the same name. Please think carefully about doing this. It may be
468better to sequentially rename your branches so that it is easier for
469others working with you to cherry-pick their local changes onto the new
470version. (XXX: needs explanation).
471
472If you want to rebase a personal topic branch, you will have to delete
473your existing topic branch and push as a new version of it. You can do
474this via the following formula (see the explanation about C<refspec>'s
475in the git push documentation for details) after you have rebased your
476branch:
477
478  # first rebase
479  % git checkout $user/$topic
480  % git fetch
481  % git rebase origin/blead
482
483  # then "delete-and-push"
484  % git push origin :$user/$topic
485  % git push origin $user/$topic
486
487B<NOTE:> it is forbidden at the repository level to delete any of the
488"primary" branches. That is any branch matching
489C<m!^(blead|maint|perl)!>. Any attempt to do so will result in git
490producing an error like this:
491
492  % git push origin :blead
493  *** It is forbidden to delete blead/maint branches in this repository
494  error: hooks/update exited with error code 1
495  error: hook declined to update refs/heads/blead
496  To ssh://perl5.git.perl.org/perl
497   ! [remote rejected] blead (hook declined)
498   error: failed to push some refs to 'ssh://perl5.git.perl.org/perl'
499
500As a matter of policy we do B<not> edit the history of the blead and
501maint-* branches. If a typo (or worse) sneaks into a commit to blead or
502maint-*, we'll fix it in another commit. The only types of updates
503allowed on these branches are "fast-forwards", where all history is
504preserved.
505
506Annotated tags in the canonical perl.git repository will never be
507deleted or modified. Think long and hard about whether you want to push
508a local tag to perl.git before doing so. (Pushing simple tags is
509not allowed.)
510
511=head2 Grafts
512
513The perl history contains one mistake which was not caught in the
514conversion: a merge was recorded in the history between blead and
515maint-5.10 where no merge actually occurred. Due to the nature of git,
516this is now impossible to fix in the public repository. You can remove
517this mis-merge locally by adding the following line to your
518C<.git/info/grafts> file:
519
520 296f12bbbbaa06de9be9d09d3dcf8f4528898a49 434946e0cb7a32589ed92d18008aaa1d88515930
521
522It is particularly important to have this graft line if any bisecting
523is done in the area of the "merge" in question.
524
525=head1 WRITE ACCESS TO THE GIT REPOSITORY
526
527Once you have write access, you will need to modify the URL for the
528origin remote to enable pushing. Edit F<.git/config> with the
529git-config(1) command:
530
531  % git config remote.origin.url git@github.com:Perl/perl5.git
532
533You can also set up your user name and e-mail address. Most people do
534this once globally in their F<~/.gitconfig> by doing something like:
535
536  % git config --global user.name "Ævar Arnfjörð Bjarmason"
537  % git config --global user.email avarab@gmail.com
538
539However, if you'd like to override that just for perl,
540execute something like the following in F<perl>:
541
542  % git config user.email avar@cpan.org
543
544It is also possible to keep C<origin> as a git remote, and add a new
545remote for ssh access:
546
547  % git remote add camel git@github.com:Perl/perl5.git
548
549This allows you to update your local repository by pulling from
550C<origin>, which is faster and doesn't require you to authenticate, and
551to push your changes back with the C<camel> remote:
552
553  % git fetch camel
554  % git push camel
555
556The C<fetch> command just updates the C<camel> refs, as the objects
557themselves should have been fetched when pulling from C<origin>.
558
559=head2 Accepting a patch
560
561If you have received a patch file generated using the above section,
562you should try out the patch.
563
564First we need to create a temporary new branch for these changes and
565switch into it:
566
567 % git checkout -b experimental
568
569Patches that were formatted by C<git format-patch> are applied with
570C<git am>:
571
572 % git am 0001-Rename-Leon-Brocard-to-Orange-Brocard.patch
573 Applying Rename Leon Brocard to Orange Brocard
574
575Note that some UNIX mail systems can mess with text attachments containing
576'From '. This will fix them up:
577
578 % perl -pi -e's/^>From /From /' \
579                        0001-Rename-Leon-Brocard-to-Orange-Brocard.patch
580
581If just a raw diff is provided, it is also possible use this two-step
582process:
583
584 % git apply bugfix.diff
585 % git commit -a -m "Some fixing" \
586                            --author="That Guy <that.guy@internets.com>"
587
588Now we can inspect the change:
589
590 % git show HEAD
591 commit b1b3dab48344cff6de4087efca3dbd63548ab5e2
592 Author: Leon Brocard <acme@astray.com>
593 Date:   Fri Dec 19 17:02:59 2008 +0000
594
595   Rename Leon Brocard to Orange Brocard
596
597 diff --git a/AUTHORS b/AUTHORS
598 index 293dd70..722c93e 100644
599 --- a/AUTHORS
600 +++ b/AUTHORS
601 @@ -541,7 +541,7 @@ Lars Hecking                 <lhecking@nmrc.ucc.ie>
602  Laszlo Molnar                  <laszlo.molnar@eth.ericsson.se>
603  Leif Huhn                      <leif@hale.dkstat.com>
604  Len Johnson                    <lenjay@ibm.net>
605 -Leon Brocard                   <acme@astray.com>
606 +Orange Brocard                 <acme@astray.com>
607  Les Peters                     <lpeters@aol.net>
608  Lesley Binks                   <lesley.binks@gmail.com>
609  Lincoln D. Stein               <lstein@cshl.org>
610
611If you are a committer to Perl and you think the patch is good, you can
612then merge it into blead then push it out to the main repository:
613
614  % git checkout blead
615  % git merge experimental
616  % git push origin blead
617
618If you want to delete your temporary branch, you may do so with:
619
620 % git checkout blead
621 % git branch -d experimental
622 error: The branch 'experimental' is not an ancestor of your current
623 HEAD.  If you are sure you want to delete it, run 'git branch -D
624 experimental'.
625 % git branch -D experimental
626 Deleted branch experimental.
627
628=head2 Committing to blead
629
630The 'blead' branch will become the next production release of Perl.
631
632Before pushing I<any> local change to blead, it's incredibly important
633that you do a few things, lest other committers come after you with
634pitchforks and torches:
635
636=over
637
638=item *
639
640Make sure you have a good commit message. See L<perlhack/Commit
641message> for details.
642
643=item *
644
645Run the test suite. You might not think that one typo fix would break a
646test file. You'd be wrong. Here's an example of where not running the
647suite caused problems. A patch was submitted that added a couple of
648tests to an existing F<.t>. It couldn't possibly affect anything else, so
649no need to test beyond the single affected F<.t>, right?  But, the
650submitter's email address had changed since the last of their
651submissions, and this caused other tests to fail. Running the test
652target given in the next item would have caught this problem.
653
654=item *
655
656If you don't run the full test suite, at least C<make test_porting>.
657This will run basic sanity checks. To see which sanity checks, have a
658look in F<t/porting>.
659
660=item *
661
662If you make any changes that affect miniperl or core routines that have
663different code paths for miniperl, be sure to run C<make minitest>.
664This will catch problems that even the full test suite will not catch
665because it runs a subset of tests under miniperl rather than perl.
666
667=back
668
669=head2 On merging and rebasing
670
671Simple, one-off commits pushed to the 'blead' branch should be simple
672commits that apply cleanly.  In other words, you should make sure your
673work is committed against the current position of blead, so that you can
674push back to the master repository without merging.
675
676Sometimes, blead will move while you're building or testing your
677changes.  When this happens, your push will be rejected with a message
678like this:
679
680 To ssh://perl5.git.perl.org/perl.git
681  ! [rejected]        blead -> blead (non-fast-forward)
682 error: failed to push some refs to 'ssh://perl5.git.perl.org/perl.git'
683 To prevent you from losing history, non-fast-forward updates were
684 rejected Merge the remote changes (e.g. 'git pull') before pushing
685 again.  See the 'Note about fast-forwards' section of 'git push --help'
686 for details.
687
688When this happens, you can just I<rebase> your work against the new
689position of blead, like this (assuming your remote for the master
690repository is "p5p"):
691
692  % git fetch p5p
693  % git rebase p5p/blead
694
695You will see your commits being re-applied, and you will then be able to
696push safely.  More information about rebasing can be found in the
697documentation for the git-rebase(1) command.
698
699For larger sets of commits that only make sense together, or that would
700benefit from a summary of the set's purpose, you should use a merge
701commit.  You should perform your work on a L<topic branch|/Topic
702branches and rewriting history>, which you should regularly rebase
703against blead to ensure that your code is not broken by blead moving.
704When you have finished your work, please perform a final rebase and
705test.  Linear history is something that gets lost with every
706commit on blead, but a final rebase makes the history linear
707again, making it easier for future maintainers to see what has
708happened.  Rebase as follows (assuming your work was on the
709branch C<< committer/somework >>):
710
711  % git checkout committer/somework
712  % git rebase blead
713
714Then you can merge it into master like this:
715
716  % git checkout blead
717  % git merge --no-ff --no-commit committer/somework
718  % git commit -a
719
720The switches above deserve explanation.  C<--no-ff> indicates that even
721if all your work can be applied linearly against blead, a merge commit
722should still be prepared.  This ensures that all your work will be shown
723as a side branch, with all its commits merged into the mainstream blead
724by the merge commit.
725
726C<--no-commit> means that the merge commit will be I<prepared> but not
727I<committed>.  The commit is then actually performed when you run the
728next command, which will bring up your editor to describe the commit.
729Without C<--no-commit>, the commit would be made with nearly no useful
730message, which would greatly diminish the value of the merge commit as a
731placeholder for the work's description.
732
733When describing the merge commit, explain the purpose of the branch, and
734keep in mind that this description will probably be used by the
735eventual release engineer when reviewing the next perldelta document.
736
737=head2 Committing to maintenance versions
738
739Maintenance versions should only be altered to add critical bug fixes,
740see L<perlpolicy>.
741
742To commit to a maintenance version of perl, you need to create a local
743tracking branch:
744
745  % git checkout --track -b maint-5.005 origin/maint-5.005
746
747This creates a local branch named C<maint-5.005>, which tracks the
748remote branch C<origin/maint-5.005>. Then you can pull, commit, merge
749and push as before.
750
751You can also cherry-pick commits from blead and another branch, by
752using the C<git cherry-pick> command. It is recommended to use the
753B<-x> option to C<git cherry-pick> in order to record the SHA1 of the
754original commit in the new commit message.
755
756Before pushing any change to a maint version, make sure you've
757satisfied the steps in L</Committing to blead> above.
758
759=head2 Using a smoke-me branch to test changes
760
761Sometimes a change affects code paths which you cannot test on the OSes
762which are directly available to you and it would be wise to have users
763on other OSes test the change before you commit it to blead.
764
765Fortunately, there is a way to get your change smoke-tested on various
766OSes: push it to a "smoke-me" branch and wait for certain automated
767smoke-testers to report the results from their OSes.
768A "smoke-me" branch is identified by the branch name: specifically, as
769seen on github.com it must be a local branch whose first name
770component is precisely C<smoke-me>.
771
772The procedure for doing this is roughly as follows (using the example of
773of tonyc's smoke-me branch called win32stat):
774
775First, make a local branch and switch to it:
776
777  % git checkout -b win32stat
778
779Make some changes, build perl and test your changes, then commit them to
780your local branch. Then push your local branch to a remote smoke-me
781branch:
782
783  % git push origin win32stat:smoke-me/tonyc/win32stat
784
785Now you can switch back to blead locally:
786
787  % git checkout blead
788
789and continue working on other things while you wait a day or two,
790keeping an eye on the results reported for your smoke-me branch at
791L<http://perl.develop-help.com/?b=smoke-me/tonyc/win32state>.
792
793If all is well then update your blead branch:
794
795  % git pull
796
797then checkout your smoke-me branch once more and rebase it on blead:
798
799  % git rebase blead win32stat
800
801Now switch back to blead and merge your smoke-me branch into it:
802
803  % git checkout blead
804  % git merge win32stat
805
806As described earlier, if there are many changes on your smoke-me branch
807then you should prepare a merge commit in which to give an overview of
808those changes by using the following command instead of the last
809command above:
810
811  % git merge win32stat --no-ff --no-commit
812
813You should now build perl and test your (merged) changes one last time
814(ideally run the whole test suite, but failing that at least run the
815F<t/porting/*.t> tests) before pushing your changes as usual:
816
817  % git push origin blead
818
819Finally, you should then delete the remote smoke-me branch:
820
821  % git push origin :smoke-me/tonyc/win32stat
822
823(which is likely to produce a warning like this, which can be ignored:
824
825 remote: fatal: ambiguous argument
826                                  'refs/heads/smoke-me/tonyc/win32stat':
827 unknown revision or path not in the working tree.
828 remote: Use '--' to separate paths from revisions
829
830) and then delete your local branch:
831
832  % git branch -d win32stat
833