=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<git-debrebase> and B<git-debpush>, and a little
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 & tag2upload'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 remote add -f origin git@salsa.debian.org:debian/foo.git
    % git push --follow-tags -u origin master

=back

The final command also has the effect of detaching your master branch from the
upstream remote, so that git doesn't try to push anything there, or merge
unreleased upstream commits.

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

=head3 Using untagged upstream commits

=over 4

Sometimes upstream does not tag their releases, or you want to package
an unreleased git snapshot.  In such a case you can create your own
upstream release tag, of the form B<upstream/>I<ver>, where I<ver> is
the upstream version you plan to put in I<debian/changelog>.  The
B<upstream/> prefix ensures that your tag will not clash with any tags
upstream later creates.

For example, suppose that the latest upstream release is 1.2.2 and you
want to package git commit ab34c21 which was made on 2013-12-11.  A
common convention is to use the upstream version number
1.2.2+git20131211.ab34c21 and so you could use

=over 4

    % git tag -s upstream/1.2.2+git20131211.ab34c21 ab34c21

=back

to obtain a release tag, and then proceed as above.

One can generate such a versioned tag using git show's --pretty option. e.g.:

=over 4

    % git tag -s upstream/$(git show --date=format:%Y%m%d --pretty=format:"1.2.2+git%cd.%h" --quiet upstream/main) upstream/main

=back

=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
    % git checkout -b upstream
    % gbp import-orig \
        --upstream-branch=upstream --debian-branch=master \
        --upstream-tag='upstream/%(version)s' \
        --sign-tags --no-pristine-tar \
        ../foo_1.2.2.orig.tar.xz
    % git branch -f upstream

=back

This should leave you on the master branch.  Next, 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.

A convenient way to ensure this requirement is satisfied is to start
by creating I<debian/gbp.conf>:

=over 4

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

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

    [import-orig]
    merge = False

=back

and commit that:

=over 4

    % git add debian/gbp.conf && git commit -m "create gbp.conf"

=back

Note that we couldn't create I<debian/gbp.conf> before now for the
same technical reasons which require our first commit to introduce
I<debian/> without patching the upstream source.  That's why we had to
pass a lot of options to our first call to gbp-import-orig(1).

=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.

If you have an existing git history that you have pushed to an
ordinary git server like B<salsa.debian.org>, we start with that.  If
you don't already have it locally, you'll need to clone it, and obtain
the corresponding orig.tar from the archive:

=over 4

    % git clone salsa.debian.org:debian/foo
    % cd foo
    % dgit setup-new-tree
    % origtargz

=back

If you don't have any existing git history, or you have history only
on the special B<dgit-repos> server, we start with B<dgit clone>:

=over 4

    % dgit clone foo
    % cd foo

=back

Then we make new upstream tags available:

=over 4

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

=back

We now use a B<git debrebase convert-from-*> command to convert your
existing history to the git-debrebase(5) data model.  Which command
you should use depends on some facts about your repository:

=over 4

=item (A) There is no delta queue.

If there do not exist any Debian patches, use

=over 4

    % git debrebase convert-from-gbp

=back

=item (B) There is a delta queue, and patches are unapplied.

This is the standard git-buildpackage(1) workflow: there are Debian
patches, but the upstream source is committed to git without those
patches applied.  Use

=over 4

    % git debrebase convert-from-gbp

=back

If you were not previously using dgit to upload your package (i.e. you
were not using the workflow described in dgit-maint-gbp(7)), and you
happen to have run B<dgit fetch sid> in this clone of the repository,
you will need to pass I<--fdiverged> to this command.

=item (C) There is a delta queue, and patches are applied.

Use

=over 4

    % git debrebase convert-from-dgit-view

=back

=back

Finally, you 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>.

=head1 GIT CONFIGURATION

git-debrebase(1) 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 fetch --tags upstream

=back

If you want to package an untagged upstream commit (because upstream
does not tag releases or because you want to package an upstream
development snapshot), see "Using untagged upstream commits" above.

=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 ../foo_1.2.3.orig.tar.xz

=back

or if you have a working watch file

=over 4

    % gbp import-orig --uscan

=back

=head2 Importing the release

=over 4

    % git debrebase new-upstream 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

Also, diff with I<--name-status> and I<--diff-filter=ADR> to see
just the list of added or removed files, which is useful to determine
whether there are any new or deleted files that 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 DEBIAN PACKAGING

Just make commits on master that change the contents of I<debian/>.

=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 -i

=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-source> (or B<dgit push-built>) 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 editing session 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
just prior to an upload, use B<dgit sbuild>, B<dgit pbuilder> or B<dgit
cowbuilder>.  Routine source-only uploads can be made by just typing

=over 4

    % git debpush

=back

The first time pass I<--quilt=linear>.  This is especially important if you
have converted the package from another workflow.  See git-debpush(1).

If you need to upload to NEW, you will need to use B<dgit push-built>.
Remember to pass I<--new> if the package is new in the target suite, and to
git push to B<salsa.debian.org> afterwards.

In some cases where you used B<git debrebase convert-from-gbp> since the last
upload, and you are uploading with dgit, it is not possible for dgit to make
your history fast-forwarding from the history on B<dgit-repos>.  In such cases
you will have to pass I<--trust-changelog> to dgit.  git-debrebase will
normally tell you if this will be needed.  (git-debpush handles this
transparently.)

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 quick
    % git debpush

=back

Note that this will introduce a new pseudomerge.

=head1 HANDLING DFSG-NON-FREE MATERIAL

=head2 Illegal material

Here we explain how to handle material that is merely DFSG-non-free.
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 DFSG-non-free: When upstream tags releases in git

Our approach is to maintain a DFSG-clean upstream branch, and create
tags on this branch for each release that we want to import.  We then
import those tags per "Importing the release", above.  In the case of
a new package, we base our initial Debianisation on our first
DFSG-clean tag.

For the first upstream release that requires DFSG filtering:

=over 4

    % git checkout -b upstream-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

=back

Now either proceed with "Importing the release" on the 1.2.3+dfsg tag,
or in the case of a new package,

=over 4

    % git branch --unset-upstream
    % git reset --hard 1.2.3+dfsg

=back

and proceed with "INITIAL DEBIANISATION".

For subsequent releases (whether or not they require additional
filtering):

=over 4

    % git checkout upstream-dfsg
    % git merge 1.2.4
    % git rm further-evil.bin # if needed
    % git commit -m "upstream version 1.2.4 DFSG-cleaned" # if needed
    % git tag -s 1.2.4+dfsg
    % git checkout master
    % # proceed with "Importing the release" on 1.2.4+dfsg tag

=back

Our upstream-dfsg 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.  Assuming that you have already set up an origin
remote per the above,

=over 4

    % git push --follow-tags -u origin master upstream-dfsg

=back

=head2 DFSG-non-free: 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.

Note that you should not try to resolve the divergent branches by
editing files in I<debian/patches>.  Changes there would either cause
trouble, or be overwritten by git-debrebase(1).

=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 can be used to 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<--trust-changelog>.

=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 simple convention you can use to minimise the number of pseudomerges
is to B<git debrebase conclude> only right before you upload or push
to B<salsa.debian.org>.

It is possible, though much less convenient, to reduce the number of
pseudomerges yet further.  We debrebase only (i) when importing a new
release, and (ii) right before uploading.  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 push and pull to and from B<salsa.debian.org> during this.  Just
before uploading, you debrebase, once, to tidy everything up.

=head2 The debian/patches directory

In this workflow, I<debian/patches> is purely an output of
git-debrebase(1).  You should not make changes there.  They will
either cause trouble, or be ignored and overwritten by
git-debrebase(1).

I<debian/patches> will often be out-of-date because git-debrebase(1)
will only regenerate it when it needs to.  So you should not rely on
the information in that directory.  When preparing patches to forward
upstream, you should use git-format-patch(1) on git commits, rather
than sending files from I<debian/patches>.

=head2 Upstream branches

In this workflow, we specify upstream tags rather than any branches.

Except when (i) upstream releases only tarballs, (ii) we require DFSG
filtering, or (iii) you also happen to be involved in upstream
development, we do not maintain any local branch corresponding to
upstream, except temporary branches used to prepare patches for
forwarding, and the like.

The idea here is that from Debian's point of view, upstream releases
are immutable points in history.  We want to make sure that we are
basing our Debian package on a properly identified upstream version,
rather than some arbitrary commit on some branch.  Tags are more
useful for this.

Upstream's branches remain available as the git remote tracking
branches for your upstream remote, e.g. I<remotes/upstream/master>.

=head2 The first ever dgit push

If this is the first ever dgit push of the package to this suite, consider
passing I<--deliberately-not-fast-forward> instead of I<--trust-changelog>.
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 Inspecting the history

The git history made by git-debrebase can seem complicated.
Here are some suggestions for helpful invocations of gitk and git.
They can be adapted for other tools like tig(1), git-log(1), magit, etc.

History of package in Debian, disregarding history from upstream:

=over

    % gitk --first-parent

In a laundered branch, the delta queue is at the top.

=back

History of the packaging, excluding the delta queue:

    % gitk :/debian :!/debian/patches

Just the delta queue (i.e. Debian's changes to upstream):

    % gitk --first-parent -- :/ :!/debian

Full history including old versions of the delta queue:

=over

    % gitk --date-order

The "Declare fast forward" commits you see have an older history
(usually, an older delta queue) as one parent,
and a newer history as the other.
--date-order makes gitk show the delta queues in the right order.

=back

Complete diff since the last upload:

=over

    % git diff dgit/dgit/sid..HEAD -- :/ :!/debian/patches

This includes changes to upstream files.

=back

Interdiff of delta queue since last upload, if you really want it:

    % git debrebase make-patches
    % git diff dgit/dgit/sid..HEAD -- debian/patches

And of course there is:

    % git debrebase status

=head2 Alternative ways to start a debrebase

Above we started an interactive debrebase by invoking git-debrebase(1)
like this:

=over 4

    % git debrebase -i

=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
    % 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 too early,
including before the most recent pseudomerge.
git-rebase without a base argument will often
start the rebase too early,
and should be avoided.
Run git-debrebase instead.
See also "ILLEGAL OPERATIONS" in git-debrebase(5).

=head1 SEE ALSO

dgit(1), dgit(7), git-debrebase(1), git-debrebase(5), gitrevisions(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.
