Bug#538620: libdrm: FTBFS with new source format 3.0 (quilt): cruft in .diff.gz

[Brice Goglin <Brice.Goglin@ens-lyon.org>]

hertzog@debian.org wrote:
> Package: libdrm
> Version: 2.4.11-1
> Severity: wishlist
> Usertags: 3.0-quilt-by-default
>
> To prepare a possible switch to the new source package format "3.0
> (quilt)" [1], I converted all source packages and rebuilt the packages
> afterwards to see what breaks, and libdrm does break. To reproduce the
> problem you can do this:
> $ apt-get source libdrm
> $ mkdir -p libdrm-2.4.11/debian/source
> $ echo "3.0 (quilt)" >libdrm-2.4.11/debian/source/format
> $ dpkg-source -b libdrm-2.4.11
> $ dpkg-source -x libdrm_2.4.11-1.dsc
> $ cd libdrm-2.4.11 && debuild -us -uc
>
> In this process, if the .diff.gz contains changes to upstream files,
> dpkg-source will have created a corresponding patch in
> debian/patches/debian-changes-2.4.11-1 and will have registered that
> patch in a quilt series (debian/patches/series, it is created if needed).
> All the patches listed in the "series" file are applied directly during
> the extraction (dpkg-source -x). quilt itself is used if available (and
> will thus lead to the creation of the .pc directory), otherwise
> dpkg-source applies the patches by itself. For more information about the
> new source package format see the manual page dpkg-source(1).
>
> In the case of libdrm, it contains changes in .diff.gz
> that is either not wanted or that should be in a separate quilt
> patch instead of there.
>
> For libdrm: it remove Changelog in .diff.gz, before it leads to empty
> files, now it's removed (and the build fails later)
>   

I can reproduce the problem but I don't understand what's going on.
Could you clarify?
thanks,
Brice