=head1 NAME

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

=head1 INTRODUCTION

This document describes elements of a workflow for maintaining a
non-native Debian package using B<dgit>.  The workflow makes the
following opinionated assumptions:

=over 4

=item

Git histories should be the non-linear histories produced by
git-merge(1), preserving all information about divergent development
that was later brought together.

=item

Maintaining convenient and powerful git workflows takes priority over
the usefulness of the raw Debian source package.  The Debian archive
is thought of as an output format.

For example, we don't spend time curating a series of quilt patches.
However,
in straightforward cases,
the information such a series would contain is readily
available from B<dgit-repos>.

=item

It is more important to have the Debian package's git history be a
descendent of upstream's git history than to use exactly the orig.tar
that upstream makes available for download.

=back

This workflow is less suitable for some packages.
When the Debian delta contains multiple pieces which interact,
or which you aren't going to be able to upstream soon,
it might be preferable to
maintain the delta as a rebasing patch series.
For such a workflow see for example
dgit-maint-debrebase(7) and dgit-maint-gbp(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.  If you want 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.  Just make commits on the
master branch, adding things in the I<debian/> directory.  If you need
to patch the upstream source, just make commits that change files
outside of the I<debian/> directory.  It is best to separate commits
that touch I<debian/> from commits that touch upstream source, so that
the latter can be cherry-picked by upstream.

Note that there is no need to 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 when
forwarding patches (see FORWARDING PATCHES UPSTREAM, below).

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 Verifying upstream's tarball releases

=over 4

It can be a good idea to compare upstream's released tarballs with the
release tags, at least for the first upload of the package.  If they
are different, you might need to add some additional steps to your
I<debian/rules>, such as running autotools.

A convenient way to perform this check is to import the tarball as
described in the following section, using a different value for
'upstream-tag', and then use git-diff(1) to compare the imported
tarball to the release tag.  If they are the same, you can use
upstream's tarball instead of running git-deborig(1).

=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

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 = upstream/%(version)s

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

    [import-orig]
    merge-mode = merge
    merge = False

=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 --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 both the
upstream source and the I<debian/> directory.

=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

Now dump any existing patch queue:

=over 4

    % git rm -rf debian/patches
    % git commit -m "drop existing quilt patch queue"

=back

Then make new upstream tags available:

=over 4

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

=back

=for dgit-test dpkg-source-ignores begin

Now you simply need to ensure that your git HEAD is dgit-compatible,
i.e., it is exactly what you would get if you ran
B<dpkg-buildpackage -i'(?:^|/)\.git(?:/|$)' -I.git -S>
and then unpacked the resultant source package.

=for dgit-test dpkg-source-ignores end

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<--trust-changelog>.  If this is the first
ever dgit push of the package, 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.)

=head1 SOURCE PACKAGE AND GIT CONFIGURATION

=head2 dgit configuration

We must tell dgit not to try to maintain
a linear queue of patches to the upstream source:

=over 4

    git config dgit.default.quilt-mode single

=back

This command should be executed in each git clone of this package, including
your co-maintainer's.  Don't set it more globally, because it is not a good
default for working on Debian source packages in general.

=head2 debian/source/options

We set a source package option to help dpkg handle
changes to the upstream
source:

=over 4

    auto-commit

=back

You don't need to create this file if you are using the version 1.0
source package format.

=head1 BUILDING AND UPLOADING

Use B<dgit build>, B<dgit sbuild>, B<dgit pbuilder>, B<dgit
cowbuilder>, B<dgit push-source>, and B<dgit push-built> as detailed in
dgit(1).  If any command fails, dgit will provide a carefully-worded
error message explaining what you should do.  If it's not clear, file
a bug against dgit.  Remember to pass I<--new> for the first upload.

If you want to upload with git-debpush(1), for the first upload you
should pass the B<--quilt=single> quilt mode option (see
git-debpush(1)).

As another alternative to B<dgit build> and friends, you can use a
tool like gitpkg(1).  This works because like dgit, gitpkg(1) enforces
that HEAD has exactly the contents of the source package.  gitpkg(1)
is highly configurable, and one dgit user reports using it to produce
and test multiple source packages, from different branches
corresponding to each of the current Debian suites.

If you want to skip dgit's checks while iterating on a problem with
the package build (for example, you don't want to commit your changes
to git), you can just run dpkg-buildpackage(1) or debuild(1) instead.

=head1 NEW UPSTREAM RELEASES

=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

In the following, replace I<1.2.3> with I<upstream/1.2.3>.

=head2 Reviewing & merging the release

It's a good idea to preview the merge of the new upstream release.
First, just check for any new or deleted files that may need
accounting for in your copyright file:

=over 4

    % git diff --name-status --diff-filter=ADR master..1.2.3 -- . ':!debian'

=back

You can then review the full merge diff:

=over 4

    % git merge-tree `git merge-base master 1.2.3` master 1.2.3 | $PAGER

=back

Once you're satisfied with what will be merged, update your package:

=over 4

    % git merge 1.2.3
    % dch -v1.2.3-1 New upstream release.
    % git add debian/changelog && git commit -m changelog

=back

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 HANDLING DFSG-NON-FREE MATERIAL

=head2 When upstream tags releases in git

We create a DFSG-clean tag to merge 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

Before merging the new 1.2.3+dfsg tag to master, you should first
determine whether it would be legally dangerous for the non-free
material to be publicly accessible in the git history on
B<dgit-repos>.

If it would be dangerous, there is a big problem;
in this case please consult your archive administrators
(for Debian this is the dgit administrator dgit-owner@debian.org
and the ftpmasters ftpmaster@ftp-master.debian.org).

=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 FORWARDING PATCHES UPSTREAM

The basic steps are:

=over 4

=item 1.

Create a new branch based off upstream's master branch.

=item 2.

git-cherry-pick(1) commits from your master branch onto your new
branch.

=item 3.

Push the branch somewhere and ask upstream to merge it, or use
git-format-patch(1) or git-request-pull(1).

=back

For example (and it is only an example):

=over 4

    % # fork foo.git on GitHub
    % git remote add -f fork git@github.com:spwhitton/foo.git
    % git checkout -b fix-error upstream/master
    % git config branch.fix-error.pushRemote fork
    % git cherry-pick master^2
    % git push
    % # submit pull request on GitHub

=back

Note that when you merge an upstream release containing your forwarded
patches, git and dgit will transparently handle "dropping" the patches
that have been forwarded, "retaining" the ones that haven't.

=head1 INCORPORATING NMUS

=over 4

    % dgit pull

=back

Alternatively, you can apply the NMU diff to your repository.  The
next push will then require I<--trust-changelog>.

=head1 SEE ALSO

dgit(1), dgit(7), 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.