The Debian packaging
has a fast forwarding history.
-The changes to upstream files are represented
+The delta queue (changes to upstream files) is represented
as a series of individual git commits,
which can worked on with rebase,
and also shared.
+=head2 DISCUSSION
+
git-debrebase is designed to work well with dgit.
git-debrebase can also be used in workflows without source packages,
-for example to work on Debian-format packages outside Debian.
+for example to work on Debian-format packages outside or alongside Debian.
-git-debrebase is not very suitable for use by Debian derivatives,
+git-debrebase
+itself is not very suitable for use by Debian derivatives,
to work on packages inherited from Debian,
because it assumes that you want to throw away any packaging
provided by your upstream.
+However, use of git-debrebase in Debian does not make anything harder for
+derivatives, and it can make some things easier.
+
+When using gitk on branches managed by git-debrebase,
+B<gitk --date-order>, B<gitk --first-parent>
+and B<gitk -- :.> (or B<gitk .>)
+produce more useful output than the default.
+
+=head1 TERMINOLOGY
+
+=over
+
+=item Pseudomerge
+
+A merge which does not actually merge the trees;
+instead, it is constructed by taking the tree
+from one of the parents
+(ignoring the contents of the other parents).
+These are used to make a rewritten history fast forward
+from a previous tip,
+so that it can be pushed and pulled normally.
+Manual construction of pseudomerges can be done with
+C<git merge -s ours>
+but is not normally needed when using git-debrebase.
+
+=item Packaging files
+
+Files in the source tree within B<debian/>,
+excluding anything in B<debian/patches/>.
+
+=item Upstream
+
+The version of the package without Debian's packaging.
+Typically provided by the actual upstream project,
+and sometimes tracked by Debian contributors in a branch C<upstream>.
+
+Upstream contains upstream files,
+but some upstreams also contain packaging files in B<debian/>.
+Any such non-upstream files found in upstream
+are thrown away by git-debrebase
+each time a new upstream version is incorporated.
+
+=item Upstream files
+
+Files in the source tree outside B<debian/>.
+These may include unmodified source from upstream,
+but also files which have been modified or created for Debian.
+
+=item Delta queue
+
+Debian's changes to upstream files:
+a series of git commits.
+
+=item Quilt patches
+
+Files in B<debian/patches/> generated for the benefit of
+dpkg-source's 3.0 (quilt) .dsc source package format.
+Not used, often deleted, and regenerated when needed
+(such as when uploading to Debian),
+by git-debrebase.
+
+=item Interchange branch; breakwater; stitched; laundered
+
+See L</BRANCHES AND BRANCH STATES - OVERVIEW>.
+
+=item Anchor; Packaging
+
+See L</BRANCH CONTENTS - DETAILED SPECIFICATION>.
+
+=item ffq-prev; debrebase-last
+
+See L</STITCHING, PSEUDO-MERGES, FFQ RECORD>.
+
+=back
=head1 DIAGRAM
------/--A!----/--B3!--%--/--> interchange view
/ / / with debian/ directory
- % % % all upstream changes applied
+ % % % entire delta queue applied
/ / / 3.0 (quilt) has debian/patches
- / / 3*
+ / / 3* "master" on Debian git servers
/ / /
2* 2* 2
/ / /
- 1 1 1 `breakwater' branch, merging baseline
+ 1 1 1 breakwater branch, merging baseline
/ / / unmodified upstream code
---@-----@--A----@--B--C plus debian/ (but no debian/patches)
- / / / no ref refers to this: we
+ / / / no ref refers to this: we
--#-----#-------#-----> upstream reconstruct its identity by
- inspecting interchange branch
+ inspecting interchange branch
Key:
1,2,3 commits touching upstream files only
-/- pseudomerge; contents are identical to
/ parent lower on diagram.
- % dgit-generated commit of debian/patches.
- `3.0 (quilt)' only; dropped by rebase tool.
+ % dgit- or git-debrebase- generated commit of debian/patches.
+ `3.0 (quilt)' only; generally dropped by git-debrebase.
* Maintainer's HEAD was here while they were editing,
before they said they were done, at which point their
- tools generated [% and] -/- commit[s] to convert to
- the fast-forwarding interchange branch. (Maybe the
- tooling is simply `dgit push'.)
+ tools made -/- (and maybe %) to convert to
+ the fast-forwarding interchange branch.
! NMUer's HEAD was here when they said `dgit push'.
Rebase branch launderer turns each ! into an
equivalent *.
-=head1 BRANCHES AND BRANCH STATES
+=head1 BRANCHES AND BRANCH STATES - OVERVIEW
git-debrebase has one primary branch,
the B<interchange branch>.
This branch is found on Debian contributor's workstations
(typically, a maintainer would call it B<master>),
in the Debian dgit git server as the suite branch (B<dgit/dgit/sid>)
-and on other git servers which support Debian owrk
+and on other git servers which support Debian work
(eg B<master> on salsa).
The interchange branch is fast-forwarding
for the same package,
stored as different local and remote git branches.
However, divergence should be avoided where possible -
-see L</STITCHING, PSEUDO-MERGES, FFQ RECORD>.
+see L</OTHER MERGES>.
A suitable interchange branch can be used directly with dgit.
In this case each dgit archive suite branch is a separate
interchange branch.
-Within the ancenstry of the interchange branch,
-there is another importnt, implicit branch, the
+Within the ancestry of the interchange branch,
+there is another important, implicit branch, the
B<breakwater>.
The breakwater contains unmodified upstream source,
but with Debian's packaging superimposed
-(replacing any C<debian/> directory that may be in upstream).
-The breakwater does not contain any representation
-of Debian's changes to upstream files.
-The breakwater starts at an B<anchor>,
+(replacing any C<debian/> directory that may be in
+the upstream commits).
+The breakwater does not contain any representation of
+the delta queue (not even debian/patches).
+The part of the breakwater processed by git-debrebase
+is the part since the most reecent B<anchor>,
which is usually a special merge generated by git-debrebase.
When working, locally,
the user's branch can be in a rebasing state,
known as B<unstitched>.
-When a branch is unstitched,
-its previous tip is recorded so that it can later be
+While a branch is unstitched,
+it is not in interchange format.
+The previous interchange branch tip
+is recorded,
+so that the previous history
+and the user's work
+can later be
stitched into the fast-forwarding interchange form.
An unstitched branch may be in
B<laundered>
state,
which means it has a more particular special form
-convenient for manipulating the changes to upstream files.
+convenient for manipulating the delta queue.
-=head1 BRANCH CONTENTS
+=head1 BRANCH CONTENTS - DETAILED SPECIFICATION
It is most convenient to describe the
-B<laundered>
-state first.
+B<breakwater>
+branch first.
+A breakwater is B<fast-forwarding>,
+but is not usually named by a ref.
It contains B<in this order> (ancestors first):
=over
An B<anchor> commit,
which is usually a special two-parent merge:
-The first parent is a previous breakwater branch,
-whose upstream files are irrelevant,
-and whose packaging files are identical to the anchor's.
-The second parent is an upstream source commit;
-whose packaging files (if any) are irrelevant,
-and whose upstream files are identical to the anchor's.
+
+The first parent
+contains the most recent version, at that point,
+of the Debian packaging (in debian/);
+it also often contains upstream files,
+but they are to be ignored.
+Often the first parent is a previous breakwater tip.
+
+The second parent
+is an upstream source commit.
+It may sometimes contain a debian/ subdirectory,
+but if so that is to be ignored.
+The second parent's upstream files
+are identical to the anchor's.
Anchor merges always contain
C<[git-debrebase anchor: ...]>
as a line in the commit message.
+
Alternatively,
an anchor may be a single-parent commit which introduces
the C<debian/> directory and makes no other changes:
Zero or more single-parent commits
containing only packaging changes.
-(And no changes to B<debian/patches/>.)
+(And no quilt patch changes.)
+
+=back
-=item Delta from upstream
+The
+B<laundered>
+branch state is B<rebasing>.
+A laundered branch is based on a breakwater
+but also contains, additionally,
+B<after> the breakwater,
+a representation of the delta queue:
+
+=over
+
+=item Delta queue commits
Zero or more single-parent commits
contaioning only changes to upstream files.
=back
-The
+The merely
B<unstitched>
-(unlaundered)
-branch state is the same,
+(ie, unstitched but unlaundered)
+branch state is also B<rebasing>.
+It has the same contents as the laundered state,
except that it may contain,
additionally,
-in B<in any order>:
+in B<in any order but after the breakwater>:
=over
and/or
to packaging,
possibly mixed within a single commit.
-(But no changes to B<debian/patches/>.)
+(But not quilt patch changes.)
-=item Patch addition for `3.0 (quilt)'
+=item Quilt patch addition for `3.0 (quilt)'
Commit(s) which add patches to B<debian/patches/>,
and add those patches to the end of B<series>.
-These are only necessary or useful when working with
+
+These are only necessary when working with
packages in C<.dsc 3.0 (quilt)> format.
+For git-debrebase they are purely an output;
+they are deleted when branches are laundered.
+git-debrebase takes care to make a proper patch
+series out of the delta queue,
+so that any resulting source packages are nice.
=back
-The
+Finally, an
B<interchange>
-branch state is the same, but may additionally contain
+branch is B<fast forwarding>.
+It has the same contents as an
+unlaundered branch state,
+but may (and usually will) additionally contain
(in some order,
possibly intermixed with the extra commits
which may be found on an unstitched unlaundered branch):
previous history.
The contributing parent is itself in interchange format.
Normally the overwritten parent is
-a previous tip of the interchange branch,
+a previous tip of an interchange branch,
but this is not necessary as the overwritten
parent is not examined.
-=item dgit dsc import
-
-Debian .dsc source package import(s) made by dgit.
-Each such import must be a two-parent pseudomerge
-whose contributing parent is in the special
-dgit format (not described further here).
-The overwritten parent must be
+If the two parents have identical trees,
+the one with the later commit date
+(or, if the commit dates are the same,
+the first parent)
+is treated as
+the contributing parent.
+
+=item dgit dsc import pseudomerge
+
+Debian .dsc source package import(s)
+made by dgit
+(during dgit fetch of a package most recently
+uploaded to Debian without dgit,
+or during dgit import-dsc).
+
+git-debrebase requires that
+each such import is in the fast-forwarding
+format produced by dgit:
+a two-parent pseudomerge,
+whose contributing parent is in the
+non-fast-forwarding
+dgit dsc import format (not described further here),
+and whose overwritten parent is
the previous interchange tip
-(and will be generated that way by normal use of dgit).
+(eg, the previous tip of the dgit suite branch).
=back
=head1 STITCHING, PSEUDO-MERGES, FFQ RECORD
Whenever the branch C<refs/B> is unstitched,
-the previous tip is recorded in the git ref C<refs/ffq-prev/heads/B>.
+the previous head is recorded in the git ref C<refs/ffq-prev/B>.
Unstiched branches are not fast forward from the published
-interchange branches. [1]
+interchange branches [1].
So before a branch can be pushed,
the right pseudomerge must be reestablished.
This is the stitch operation,
which consumes the ffq-prev ref.
-When the user has an unstituched branch,
+When the user has an unstitched branch,
they may rewrite it freely,
from the breakwater tip onwards.
Such a git rebase is the default operation for git-debrebase.
to sharing any other rebasing git branch.
[1] Strictly, for a package
-which has never had Debian changes to upstream files,
+which has never had a Debian delta queue,
the interchange and breakwater branches may be identical,
in which case the unstitched branch is fast forward
from the interchange branch and no pseudomerge is needed.
+When ffq-prev is not present,
+C<refs/debrebase-last/B> records some ancestor of refs/B,
+(usually, the result of last stitch).
+This can be used to quickly determine whether refs/B
+is being maintained in git-debrebase form.
+
=head1 OTHER MERGES
Note that the representation described here does not permit
For this reason the tools will try to help the user
avoid divergence of the interchange branch.
+See dgit-maint-rebase(7)
+for a discussion of what kinds of behaviours
+should be be avoided
+because
+they might generate such merges.
+
Automatic resolution of divergent interchange branches
(or laundering of merges on the interchange branch)
is thought to be possible,
in principle tolerable,
but each of the parents would have to be, in turn,
a breakwater,
-and difficult qeustions arise if they don't have the same anchor.
+and difficult questions arise if they don't have the same anchor.
We use the commit message annotation to
distinguish the special anchor merges from other general merges,
so we can at least detect unsupported merges.
-=head1 TERMINOLOGY
+=head1 LEGAL OPERATIONS
+
+The following basic operations follows from this model
+(refer to the diagram above):
=over
-=item Pseudomerge
+=item Append linear commits
-A merge which does not actually merge the trees;
-instead, it takes its tree by construction from one parent.
-These are used to make a rewritten history fast forward
-from a previous tip,
-so that it can be pushed and pulled normally.
-Manual construction of pseudomerges can be done with
-C<git merge -s ours>
-but is not normally needed when using git-debrebase.
+No matter the branch state,
+it is always fine to simply git commit
+(or cherry-pick etc.)
+commits containing upstream file changes, packaging changes,
+or both.
-=item Packaging files
+(This may make the branch unlaundered.)
-Files in the source tree within B<debian/>.
-(Does not include anything which may exist in B<debian/patches/>.)
+=item Launder branch
-=item Upstream
+Record the previous head in ffq-prev,
+if we were stitched before
+(and delete debrebase-last).
-The version of the package without Debian's packaging.
-Typically provided by the actual upstream project,
-and often tracked by Debian contributors in a branch C<upstream>.
+Reorganise the current branch so that the packaging
+changes come first,
+followed by the delta queue,
+turning C<-@-A-1-2-B3> into C<...@-A-B-1-2-3>.
-=item Upstream files
+Drop pseudomerges and any quilt patch additions.
-Files in the source tree outside B<debian/>.
-These may include unmodified source from upstream,
-but also files which have been modified or created for Debian.
+=item Interactive rebase
+
+With a laundered branch,
+one can do an interactive git rebase of the delta queue.
+
+=item New upstream rebase
+
+Start rebasing onto a new upstream version,
+turning C<...#..@-A-B-1-2-3> into C<(...#..@-A-B-, ...#'-)@'-1-2>.
+
+This has to be a wrapper around git-rebase,
+which prepares @' and then tries to rebase 1 2 onto @'.
+If the user asks for an interactive rebase,
+@' doesn't appear in the commit list, since
+@' is the newbase of the rebase (see git-rebase(1)).
+
+Note that the construction of @' cannot fail
+because @' simply copies debian/ from B and and everything else from #'.
+(Rebasing A and B is undesirable.
+We want the debian/ files to be non-rebasing
+so that git log shows the packaging history.)
+
+=item Stitch
+
+Make a pseudomerge,
+whose contributing parent to is the unstitched branch
+and
+whose overwritten parent is ffq-prev,
+consuming ffq-prev in the process
+(and writing debrebase-last instead).
+Ideally the contributing parent would be a laundered branch,
+or perhaps a laundered branch with a quilt patch addition commit.
+
+=item Commit quilt patches
+
+To generate a tree which can be represented as a
+3.0 (quilt) .dsc source packages,
+the delta queue must be reified inside the git tree
+in B<debian/patches/>.
+These patch files can be stripped out and/or regenerated as needed.
+
+=back
+
+=head1 ILLEGAL OPERATIONS
+
+Some git operations are not permitted in this data model.
+Performing them will break git-debrebase.
+
+=over
+
+=item General merges
+
+See L</OTHER MERGES>, above.
+
+=item git-rebase starting too soon, or without base argument
+
+git-rebase must not be invoked in such a way that
+the chosen base is before the anchor,
+or before the last pseudomerge.
+This is because git-rebase mangles merges.
+git rebase --preserve-merges is also dangerous.
+
+git-rebase without a base argument will often start too early.
+
+For these reasons,
+it is better to use git-debrebase and
+let it choose the base
+for your rebase.
+If you do realise you have make this mistake,
+it is best to use the reflog to recover to a suitable
+good previous state.
+
+=item Editing debian/patches
+
+debian/patches is an output from git-debrebase,
+not an input.
+If you edit patches git-debrebase will complain
+and refuse to work.
+If you add patches your work is likely to be discarded.
+
+Instead of editing patches,
+use git-debrebase to edit the corresponding commits.
+
+=back
+
+=head1 COMMIT MESSAGE ANNOTATIONS
+
+git-debrebase makes annotations
+in the messages of commits it generates.
+
+The general form is
+
+ [git-debrebase[ COMMIT-TYPE [ ARGS...]]: PROSE, MORE PROSE]
+
+git-debrebase treats anything after the colon as a comment,
+paying no attention to PROSE.
+
+The full set of annotations is:
+ [git-debrebase: split mixed commit, debian part]
+ [git-debrebase: split mixed commit, upstream-part]
+ [git-debrebase: convert dgit import, debian changes]
+ [git-debrebase anchor: convert dgit import, upstream changes]
+
+ [git-debrebase upstream-combine . PIECE[ PIECE...]: new upstream]
+ [git-debrebase anchor: new upstream NEW-UPSTREAM-VERSION, merge]
+ [git-debrebase: new upstream NEW-UPSTREAM-VERSION, changelog]
+ [git-debrebase: export and commit patches]
+
+ [git-debrebase convert-from-gbp: drop patches]
+ [git-debrebase anchor: declare upstream]
+ [git-debrebase pseudomerge: stitch]
+
+ [git-debrebase convert-to-gbp: commit patches]
+
+Only anchor merges have the C<[git-debrebase anchor: ...]> tag.
+Single-parent anchors are not generated by git-debrebase,
+and when made manually should not
+contain any C<[git-debrebase ...]> annotation.
+
+The C<split mixed commit> and C<convert dgit import>
+tags are added to the pre-existing commit message,
+when git-debrebase rewrites the commit.
+
+=head1 APPENDIX - DGIT IMPORT HANDLING
+
+The dgit .dsc import format is not documented or specified
+(so some of the following terms are not defined anywhere).
+The dgit import format it is defined by the implementation in dgit,
+of which git-debrebase has special knowledge.
+
+Consider a non-dgit NMU followed by a dgit NMU:
+
+ interchange --/--B3!--%--//----D*-->
+ / /
+ % 4
+ / 3
+ / 2
+ / 1
+ 2 &_
+ / /| \
+ 1 0 00 =XBC%
+ /
+ /
+ --@--A breakwater
+ /
+ --#--------> upstream
+
+
+ Supplementary key:
+
+ =XBC% dgit tarball import of .debian.tar.gz containing
+ Debian packaging including changes B C and quilt patches
+ 0 dgit tarball import of upstream tarball
+ 00 dgit tarball import of supplementary upstream piece
+ &_ dgit import nearly-breakwater-anchor
+ // dgit fetch / import-dsc pseudomerge to make fast forward
+
+ &' git-debrebase converted import (upstream files only)
+ C' git-debrebase converted packaging change import
+
+ * ** before and after HEAD
+
+We want to transform this into:
+
+=over
+
+=item I. No new upstream version
+
+ (0 + 00 eq #)
+ --/--B3!--%--//-----D*-------------/-->
+ / / /
+ % 4 4**
+ / 3 3
+ / 2 2
+ / 1 1
+ 2 &_ /
+ / /| \ /
+ 1 0 00 =XBC% /
+ / /
+ / /
+ --@--A-----B---------------------C'---D
+ /
+ --#----------------------------------------->
+
+=item II. New upstream
+
+ (0 + 00 neq #)
+
+ --/--B3!--%--//-----D*-------------/-->
+ / / /
+ % 4 4**
+ / 3 3
+ / 2 2
+ / 1 1
+ 2 &_ /
+ / /| \ /
+ 1 0 00 =XBC% /
+ / /
+ / /
+ --@--A-----B-----------------@---C'---D
+ / /
+ --#--------------------- - - / - - --------->
+ /
+ &'
+ /|
+ 0 00
=back
=head1 SEE ALSO
-dgit(1), dgit(7), dgit-maint-*(7)
+git-debrebase(1),
+dgit-maint-rebase(7),
+dgit(1)
~ianmdlvl / dgit.git / blobdiff