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=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.

If you prefer linear histories, see dgit-maint-rebase(7).

=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, 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

=head1 GIT CONFIGURATION

Add the following to your ~/.gitconfig to teach git-archive(1) how to
compress orig tarballs:

=over 4

    [tar "tar.xz"]
        command = xz -c
    [tar "tar.gz"]
        command = gzip -c

=back

=head1 INITIAL DEBIANISATION

=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 detachs 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<alioth.debian.org> in addition to B<dgit-repos>, you can
do something like this:

=over 4

    % git remote add -f origin git.debian.org:/git/collab-maint/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.  Generate one with git-archive(1):

=over 4

    % git archive -o ../foo_1.2.2.orig.tar.xz 1.2.2

=back

If you are using the version 1.0 source package format, replace 'xz'
with 'gz'.

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

=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 = upsteram
    debian-branch = master
    upstream-tag = %(version)s

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

=back

Then we can import the upstream version:

=over 4

    % git add debian/gbp.conf && git commit -m "create gbp.conf"
    % gbp import-orig ../foo_1.2.2.orig.tar.xz

=back

You are now ready to proceed as above, making commits to both the
upstream source and the I<debian/> directory.

If you want to maintain a copy of your repository on
B<alioth.debian.org>, you should push both the origin and the upstream
branches:

=over 4

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

=back

=head1 SOURCE PACKAGE CONFIGURATION

=head2 debian/source/options

We set some source package options such that dgit can transparently
handle the "dropping" and "refreshing" of changes to the upstream
source:

=over 4

    single-debian-patch
    auto-commit

=back

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

=head2 Sample text for README.source

It is a good idea to explain how a user can obtain a break down of the
changes to the upstream source:

=over 4

The Debian packaging of foo is maintained using dgit.  For the sake of
an efficient workflow, Debian modifications to the upstream source are
squashed into a single patch, rather than a series of quilt patches.
To obtain a patch queue for package version 1.2.3-1:

=over 4

    # apt-get install dgit
    % dgit clone foo
    % cd foo
    % git log --oneline 1.2.3..debian/1.2.3-1 -- . ':!debian'

=back

See dgit(1), dgit(7) and dgit-maint-merge(7) for more information.

=back

=head1 BUILDING AND UPLOADING

Use B<dgit build>, B<dgit sbuild>, B<dgit build-source>, and B<dgit
push> 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.

As an 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 When upstream tags releases in git

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 remote update
    % git diff --stat 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 archive ../foo_1.2.3.orig.tar.xz 1.2.3
    % git merge 1.2.3
    % dch -v1.2.3-1 New upstream release.
    % git add debian/changelog && git commit -m changelog

=back

and you are ready to try a build.

Again, if you are using the version 1.0 source package format, replace
'xz' with 'gz'.

=head2 When upstream releases only tarballs

Either

=over 4

    % gbp import-orig ../foo_1.2.2.orig.tar.xz

=back

or if you have a working watch file

=over 4

    % gbp import-orig --uscan

=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, pass B<--squash> to git-merge(1).

=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<--overwrite>.

=head1 SEE ALSO

dgit(1), dgit(7)

=head1 AUTHOR

This tutorial was written and is maintained by Sean Whitton <spwhitton@spwhitton.name>.