=head1 NAME

dgit - tips for maintaining official Debian backports

=head1 INTRODUCTION

This document describes elements of a workflow for using B<dgit> to
maintain an official Debian backport.  We do not assume that whoever
uploads the package to Debian unstable is using B<dgit>.

=head1 GENERAL TIPS

The first time a package is backported
for any particular Debian release,
you will have to pass the --new option to dgit.

=head1 TERMINOLOGY

Let the I<master> branch contain the packaging history uploaded to
Debian unstable, and the I<bookworm-bpo> branch be where you prepare
your uploads to the B<bookworm-backports> suite.

A B<merging> backports workflow means that each time an upload
migrates to Debian testing and you want to prepare an upload to
B<bookworm-backports>, you do something like this:

=over 4

    % git checkout bookworm-bpo
    % git merge master
    % dch --bpo
    % # any other changes needed for backporting
    % git commit -a
    % # try a build

=back

A B<rebasing> backports workflow means that you throw away the history
of the I<bookworm-bpo> branch each time a new version migrates to Debian
testing, something equivalent to this:

=over 4

    % git checkout -B bookworm-bpo master
    % dch --bpo
    % # any other changes needed for backporting
    % git commit -a
    % # try a build

=back

If you use a merging backports workflow, your changelog contains
entries for each previous upload to B<bookworm-backports>; in a rebasing
workflow, it contains only the latest.

=head1 CHOOSING BETWEEN THE TWO WORKFLOWS

If backporting involves making no (additional) changes to the upstream
source, whether you use a merging or rebasing backports workflow is a
matter of personal preference.  There are good arguments in favour of
both workflows fitting the semantics of the B<*-backports> suites.

One thing that can break the tie is that if you want to upload with
B<git-debpush>, then, at present, you must use a merging workflow.
Though, note that your first upload to backports must always be done with
B<dgit>, because it is not a source-only upload.

If you have to make changes to the upstream source to make the package
work on machines running Debian stable, it is advisable to choose a
rebasing workflow.  This ensures that dgit can automatically update
the debian/patches directory without any manual intervention.

=head1 TIPS FOR A MERGING WORKFLOW

=head2 Use dgit's branches

If you do not yourself upload the package to Debian unstable, it is
usually easiest to use dgit's branches, and ignore the configured
Vcs-Git repository.

You would use

=over 4

    % dgit clone foo bookworm

=back

for a new backport of package 'foo' to B<bookworm-backports>, and then

=over 4

    % dgit fetch bookworm
    % git merge dgit/dgit/bookworm

=back

when new versions migrate to Debian testing.

If you follow this suggestion then there is nothing pushed to salsa, so you
will always need to use B<dgit> to upload, not B<git-debpush>.

=head1 TIPS FOR A REBASING WORKFLOW

=head2 Use dgit's branches

If you do not yourself upload the package to Debian unstable, it is
usually easiest to use dgit's branches, and ignore the configured
Vcs-Git repository.  For each new version from Debian testing, you
would

=over 4

    % dgit fetch bookworm
    % git checkout -B bookworm-bpo dgit/dgit/bookworm
    % # use git-cherry-pick(1) to (re)apply any needed backporting fixes

=back

=head2 Overwriting

B<dgit push> tries hard to prevent you from accidentally overwriting
uploads that it thinks aren't represented in the git history you are
trying to upload.  This is mainly to prevent accidentally overwriting
NMUs.

With a rebasing backports workflow, dgit will think that every upload
of a new version from Debian testing might be accidentally overwriting
uploads.  You will need to explicitly indicate the upload to
B<bookworm-backports> you wish to overwrite.

Suppose that the last upload to B<bookworm-backports> was versioned
I<1.2.2-1~bpo10+1> and you have now prepared I<1.2.3-1~bpo10+1> for
upload.  When you B<dgit push>, you will need to pass
I<--trust-changelog=1.2.2-1~bpo10+1>.

Alternatively, you can perform the pseudomerge that I<--trust-changelog>
would have done yourself:

=over 4

    % dgit fetch bookworm-backports
    % git merge -s ours dgit/dgit/bookworm-backports
    % dgit push-source

=back

=head1 SEE ALSO

dgit(1), dgit(7), https://backports.debian.org/

=head1 AUTHOR

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