We would like to: represent the input tarballs as a commit each (which
all get merged together as if by git merge -s subtree), and for quilt
packages, each patch as a commit. But w want to avoid (as much as
possible) reimplementing the package extraction algorithm in
dpkg-source does not currently provide interfaces that look like they
are intended for what dgit wants to do. And dgit wants to work with
old versions of dpkg, so I have implemented the following algorithm
rather than wait for such interfaces added (even supposing that a sane
interface could be designed, which is doubtful):
* dgit will untar each input tarball.
This will be done by scanning the .dsc for things whose names look
like (compressed) tarballs, and using the interfaces provided by
Dpkg::Compression to get at the tarball.
Each input tarball unpack will be done separately, and will be
followed by git add and git write-tree, to obtain a git tree object
corresponding to the tarball contents.
That tree object will be made into a commit object with no parents.
(The package changelog will be searched for the earliest version
with the right upstream version component, and the information found
there used for the commit object's metadata.)
* For `3.0 (quilt), dgit will run
dpkg-source -x --skip-patches
git plumbing will be used to make the result into a tree and a
commit. The commit will have as parents all the tarballs previously
mentioned. The main orig tarball will be the leftmost parent and
the debian tarball the rightmost parent. The metadata will come
from the .dsc and/or the final changelog entry.
dgit will then dpkg-source --before-build and record the resulting
Then, dgit will switch back to the patches-unapplied version and use
`gbp pq import' (in the private working area) to turn the
patches-unapplied tree into a patches-applied one.
Finally dgit will check that the gbp pq generated patches-applied
version has the same git tree object as the one generated by
* For source formats other than `3.0 (quilt)', dgit will do simply
Again, it will make that into a tree and a commit.
* For source formats with only single file entry in the .dsc, the
(one) tarball is not imported separately (since its tree object
would be the same as the extracted object), and the commit of the
dpkg-source -x output has no parents.
* As currently, there will be a final no-change-to-the-tree
pseudomerge commit which stitches the package into the relevant dgit
suite branch. (By `pseudomerge' we mean something that looks as if
it was made with git merge -s ours.)
* As currently, dgit will take steps so that none of the git trees
discussed above contain a .pc directory.
This has the following properties:
* Each input tarball is represented by a different commit; in usual
cases these commits will be the same for every upload of the same
* For `3.0 (quilt)' each patch's changes to the upstream files appears
as a single git commit (as is the effect of the debian tarball);
also, there is a commit object whose tree is just the debian/
directory, which might well be the same as certain debian-only git
* For `1.0' non-native, the effect of the diff is represented as a
commit. So eg `git blame' will show synthetic commits corresponding
to the correct parts of the input source package.
* It is possible to `git cherry-pick' etc. commits representing `3.0
(quilt)' patches. It is even possible fish out the patch stack as
git branch and rebase it elsewhere etc., since the patch stack is
represented as a contiguous series of commits which make only the
relevant upstream changes.
* Every orig tarball in the source package is decompressed twice, but
disk space for only one extra copy of its unpacked contents is
needed. (The converse would be possible in principle but would be
very hard to arrange with the current interfaces provided by the
* No back doors into the innards of dpkg-source (nor changes to
dpkg-dev) are required.
* dgit does grow a dependency on git-buildpackage.
* Knowledge of the source format embedded in dgit is is restricted to
some relatively straightforward processing of filenames found in
* dgit now depends on dpkg-source -x --skip-patches followed by
dpkg-source --before-build being the same as dpkg-source -x
(for `3.0 (quilt)').