[dgit.git] / dgit-maint-debrebase.7.pod

=head1 NAME

dgit - tutorial for package maintainers, using a workflow centered around git-debrebase(1)

=head1 INTRODUCTION

This document describes elements of a workflow for maintaining a
non-native Debian package using B<dgit>.  We maintain the Debian delta
as a series of git commits on our master branch.  We use
git-debrebase(1) to shuffle our branch such that this series of git
commits appears at the end of the branch.  All the public git history
is fast-forwarding, i.e., we do not rewrite and force-push.

Some advantages of this workflow:

=over 4

=item

Manipulate the delta queue using the full power of git-rebase(1),
instead of relying on quilt(1), and without having to switch back and
forth between patches-applied and patches-unapplied branches when
committing changes and trying to build, as with gbp-pq(1).

=item

If you are using 3.0 (quilt), provide your delta queue as a properly
separated series of quilt patches in the source package that you
upload to the archive (unlike with dgit-maint-merge(7)).

=item

Avoid the git tree being dirtied by the application or unapplication
of patches, as they are always applied.

=item

Benefit from dgit's safety catches.  In particular, ensure that your
upload always matches exactly your git HEAD.

=item

Provide your full git history in a standard format on B<dgit-repos>,
where it can benefit downstream dgit users, such as people using dgit
to do an NMU (see dgit-nmu-simple(7) and dgit-user(7)).

=item

Minimise the amount you need to know about 3.0 (quilt) in order to
maintain Debian source packages which use that format.

=back

This workflow is appropriate for packages where the Debian delta
contains multiple pieces which interact, or which you don't expect to
be able to upstream soon.  For packages with simple and/or short-lived
Debian deltas, use of git-debrebase(1) introduces unneeded complexity.
For such packages, consider the workflow described in
dgit-maint-merge(7).

=head1 INITIAL DEBIANISATION

This section explains how to start using this workflow with a new
package.  It should be skipped when converting an existing package to
this workflow.

=head2 When upstream tags releases in git

Suppose that the latest stable upstream release is 1.2.2, and this has
been tagged '1.2.2' by upstream.

=over 4

    % git clone -oupstream https://some.upstream/foo.git
    % cd foo
    % git verify-tag 1.2.2
    % git reset --hard 1.2.2
    % git branch --unset-upstream

=back

The final command detaches your master branch from the upstream
remote, so that git doesn't try to push anything there, or merge
unreleased upstream commits.  To maintain a copy of your packaging
branch on B<salsa.debian.org> in addition to B<dgit-repos>, you can do
something like this:

=over 4

    % git remote add -f origin salsa.debian.org:Debian/foo.git
    % git push --follow-tags -u origin master

=back

Now go ahead and Debianise your package.  Make commits on the master
branch, adding things in the I<debian/> directory, or patching the
upstream source.  For technical reasons, B<it is essential that your
first commit introduces the debian/ directory containing at least one
file, and does nothing else.> In other words, make a commit
introducing I<debian/> before patching the upstream source.

Finally, you need an orig tarball:

=over 4

    % git deborig

=back

See git-deborig(1) if this fails.

This tarball is ephemeral and easily regenerated, so we don't commit
it anywhere (e.g. with tools like pristine-tar(1)).

=head3 Comparing upstream's tarball releases

=over 4

The above assumes that you know how to build the package from git and
that doing so is straightforward.

If, as a user of the upstream source, you usually build from upstream
tarball releases, rather than upstream git tags, you will sometimes
find that the git tree doesn't contain everything that is in the
tarball.

Additional build steps may be needed.  For example, you may need your
I<debian/rules> to run autotools.

You can compare the upstream tarball release, and upstream git tag,
within git, by importing the tarball into git as described in the
next section, using a different value for 'upstream-tag', and then
using git-diff(1) to compare the imported tarball to the release tag.

=back

=head2 When upstream releases only tarballs

Because we want to work in git, we need a virtual upstream branch with
virtual release tags.  gbp-import-orig(1) can manage this for us.  To
begin

=over 4

    % mkdir foo
    % cd foo
    % git init

=back

Now create I<debian/gbp.conf>:

=over 4

    [DEFAULT]
    upstream-branch = upstream
    debian-branch = master
    upstream-tag = %(version)s

    sign-tags = True
    pristine-tar = False
    pristine-tar-commit = False

    [import-orig]
    merge-mode = merge

=back

gbp-import-orig(1) requires a pre-existing upstream branch:

=over 4

    % git add debian/gbp.conf && git commit -m "create gbp.conf"
    % git checkout --orphan upstream
    % git rm -rf .
    % git commit --allow-empty -m "initial, empty branch for upstream source"
    % git checkout -f master

=back

Then we can import the upstream version:

=over 4

    % gbp import-orig --merge-mode=replace ../foo_1.2.2.orig.tar.xz

=back

Our upstream branch cannot be pushed to B<dgit-repos>, but since we
will need it whenever we import a new upstream version, we must push
it somewhere.  The usual choice is B<salsa.debian.org>:

=over 4

    % git remote add -f origin salsa.debian.org:Debian/foo.git
    % git push --follow-tags -u origin master upstream

=back

You are now ready to proceed as above, making commits to the
I<debian/> directory and to the upstream source.  As above, for
technical reasons, B<it is essential that your first commit introduces
the debian/ directory containing at least one file, and does nothing
else.>  In other words, make a commit introducing I<debian/> before
patching the upstream source.

=head1 CONVERTING AN EXISTING PACKAGE

This section explains how to convert an existing Debian package to
this workflow.  It should be skipped when debianising a new package.

=head2 No existing git history

=over 4

    % dgit clone foo
    % cd foo
    % git remote add -f upstream https://some.upstream/foo.git

=back

=head2 Existing git history using another workflow

First, if you don't already have the git history locally, clone it,
and obtain the corresponding orig.tar from the archive:

=over 4

    % git clone salsa.debian.org:Debian/foo
    % cd foo
    % origtargz

=back

If your tree is patches-unapplied, you will need to make a commit
corresponding to each of the quilt patches.  You can use

=over 4

    git debrebase convert-from-gbp

=back

Then make new upstream tags available:

=over 4

    % git remote add -f upstream https://some.upstream/foo.git

=back

Now you simply need to ensure that your git HEAD is dgit-compatible,
i.e., it is exactly what you would get if you deleted .git, invoked
B<dpkg-buildpackage -S>, and then unpacked the resultant source
package.

To achieve this, you might need to delete
I<debian/source/local-options>.  One way to have dgit check your
progress is to run B<dgit build-source>.

The first dgit push will require I<--overwrite>.

=head1 GIT CONFIGURATION

git-debrebase does not yet support using B<git merge> to merge
divergent branches of development (see "OTHER MERGES" in
git-debrebase(5)).  You should configure git such that B<git pull>
does not try to merge:

=over 4

    % git config --local pull.rebase true

=back

Now when you pull work from other Debian contributors, git will rebase
your work on top of theirs.

If you use this clone for upstream development in addition to
Debian packaging work, you may not want to set this global setting.
Instead, see the B<branch.autoSetupRebase> and
B<branch.E<lt>nameE<gt>.rebase> settings in git-config(5).

=head1 IMPORTING NEW UPSTREAM RELEASES

There are two steps: obtaining git refs that correspond to the new
release, and importing that release using git-debrebase(1).

=head2 Obtaining the release

=head3 When upstream tags releases in git

=over 4

    % git remote update

=back

=head3 When upstream releases only tarballs

You will need the I<debian/gbp.conf> from "When upstream releases only
tarballs", above.  You will also need your upstream branch.  Above, we
pushed this to B<salsa.debian.org>.  You will need to clone or fetch
from there, instead of relying on B<dgit clone>/B<dgit fetch> alone.

Then, either

=over 4

    % gbp import-orig --no-merge ../foo_1.2.3.orig.tar.xz

=back

or if you have a working watch file

=over 4

    % gbp import-orig --no-merge --uscan

=back

=head2 Importing the release

=over 4

    % git debrebase new-upstream-v0 1.2.3

=back

This invocation of git-debrebase(1) involves a git rebase.  You may
need to resolve conflicts if the Debian delta queue does not apply
cleanly to the new upstream source.

If all went well, you can now review the merge of the new upstream
release:

=over 4

    git diff debian/1.2.2-1..HEAD -- . ':!debian'

=back

Pass I<--stat> just to see the list of changed files, which is useful
to determine whether there are any new or deleted files to may need
accounting for in your copyright file.

If you obtained a tarball from upstream, you are ready to try a build.
If you merged a git tag from upstream, you will first need to generate
a tarball:

=over 4

    % git deborig

=back

=head1 EDITING THE DELTA QUEUE

=head2 Adding new patches

Adding new patches is straightforward: just make commits touching only
files outside of the I<debian/> directory.  You can also use tools
like git-revert(1), git-am(1) and git-cherry-pick(1).

=head2 Editing patches: starting a debrebase

git-debrebase(1) is a wrapper around git-rebase(1) which allows us to
edit, re-order and delete patches.  Run

=over 4

    % git debrebase

=back

to start an interactive rebase.  You can edit, re-order and delete
commits just as you would during B<git rebase -i>.

=head2 Editing patches: finishing a debrebase

After completing the git rebase, your branch will not be a
fast-forward of the git HEAD you had before the rebase.  This means
that we cannot push the branch anywhere.  If you are ready to upload,
B<dgit push> or B<dgit push-source> will take care of fixing this up
for you.

If you are not yet ready to upload, and want to push your branch to a
git remote such as B<salsa.debian.org>,

=over 4

    % git debrebase conclude

=back

Note that each time you conclude a debrebase you introduce a
pseudomerge into your git history, which may make it harder to read.
Try to do all of the editing of the delta queue that you think will be
needed for this upload in a single debrebase, so that there is a
single debrebase stitch.

=head1 BUILDING AND UPLOADING

You can use dpkg-buildpackage(1) for test builds.  When you are ready
to build for an upload, use B<dgit sbuild>.

Upload with B<dgit push> or B<dgit push-source>.  Remember to pass
I<--new> if the package is new in the target suite.

Right before uploading, if you did not just already do so, you might
want to have git-debrebase(1) shuffle your branch such that the Debian
delta queue appears right at the tip of the branch you will push:

=over 4

    % git debrebase launder
    % dgit push-source

=back

Note that this will introduce a new pseudomerge.

After dgit pushing, be sure to git push to B<salsa.debian.org>, if
you're using that.

=head1 HANDLING DFSG-NON-FREE MATERIAL

This covers only DFSG-non-free material.  Material which is legally
dangerous (for example, files which are actually illegal) cannot be
handled this way.

If you encounter possibly-legally-dangerous material in the upstream
source code you should seek advice.  It is often best not to make a
fuss on a public mailing list (at least, not at first).  Instead,
email your archive administrators.  For Debian that is
 To: dgit-owner@debian.org, ftpmaster@ftp-master.debian.org

=head2 When upstream tags releases in git

We create a DFSG-clean tag to import to master:

=over 4

    % git checkout -b pre-dfsg 1.2.3
    % git rm evil.bin
    % git commit -m "upstream version 1.2.3 DFSG-cleaned"
    % git tag -s 1.2.3+dfsg
    % git checkout master
    % git branch -D pre-dfsg

=back

=head2 When upstream releases only tarballs

The easiest way to handle this is to add a B<Files-Excluded> field to
I<debian/copyright>, and a B<uversionmangle> setting in
I<debian/watch>.  See uscan(1).  Alternatively, see the I<--filter>
option detailed in gbp-import-orig(1).

=head1 INCORPORATING NMUS

In the simplest case,

=over 4

    % dgit fetch
    % git merge --ff-only dgit/dgit/sid

=back

If that fails, because your branch and the NMUers work represent
divergent branches of development, you have a number of options.  Here
we describe the two simplest.

=head2 Rebasing your work onto the NMU

=over 4

    % git rebase dgit/dgit/sid

=back

If the NMUer added new commits modifying the upstream source, you will
probably want to debrebase before your next upload to tidy those up.

For example, the NMUer might have used git-revert(1) to unapply one of
your patches.  A debrebase will strip both the patch and the reversion
from the delta queue.

=head2 Manually applying the debdiff

If you cannot rebase because you have already pushed to
B<salsa.debian.org>, say, you can manually apply the NMU debdiff,
commit and debrebase.  The next B<dgit push> will require
I<--overwrite>.

=head1 HINTS AND TIPS

=head2 Minimising pseudomerges

Above we noted that each time you conclude a debrebase, you introduce
a pseudomerge into your git history, which may make it harder to read.

A convention you can use to minimise the number of pseudomerges is to
debrebase only right before you upload.

Before that point, instead of editing the existing delta queue, you
append fixup commits (and reversions of commits) that alter the
upstream source to the required state.  You can freely push and pull
from B<salsa.debian.org> during this.  Just before uploading, you
debrebase, once, to tidy everything up.

=head2 Upstream branches

Except in the case where upstream releases only tarballs, we do not
maintain a separate 'upstream' branch (unless you also happen to be
involved in upstream development).  We work with upstream tags rather
than any branches, except temporary branches used to prepare patches
for forwarding upstream, for example.

The thought behind this is that branches are things to which one
expects to commit, while tags are immutable points in history.  From
the Debian point of the view, the upstream source is immutable.  It's
our packaging to which we expect to commit.

=head2 The first ever dgit push

If this is the first ever dgit push of the package, consider passing
I<--deliberately-not-fast-forward> instead of I<--overwrite>.  This
avoids introducing a new origin commit into your git history.  (This
origin commit would represent the most recent non-dgit upload of the
package, but this should already be represented in your git history.)

=head2 Alternative ways to start a debrebase

Above we started an interactive debrebase by invoking git-debrebase(1)
without any arguments, i.e.

=over 4

    % git debrebase

=back

It is also possible to perform a non-interactive rebase, like this:

=over 4

    % git debrebase -- [git-rebase options...]

=back


A third alternative is to have git-debrebase(1) shuffle all the Debian
changes to the end of your branch, and then manipulate them yourself
using git-rebase(1) directly.  For example,

=over 4

    % git debrebase launder
    % git rebase -i HEAD~5      # there are 4 Debian patches

=back

If you take this approach, you should be very careful not to start the
rebase earlier than the beginning of the delta queue.

=head1 SEE ALSO

dgit(1), dgit(7)

=head1 AUTHOR

This tutorial was written and is maintained by Sean Whitton
<spwhitton@spwhitton.name>.  It contains contributions from other dgit
contributors too - see the dgit copyright file.