Build Debian packages out-of-tree

Debians dpkg-buildpackage has the annoying feature, that the build artifacts are placed in the parent directory. Bug 657491 requested that feature in 2012, but there still is no such option. While working on speeding up the build process I investigated, how that could be fixed or at least be worked around.

Building a package by default involves the following programs calling each other:

  • debuild
    • dpkg-buildpackage
      • dpkg-source --build $dir../$pkg_$ver.dsc
      • make -f debian/rules
        • dpkg-deb --build $dir $deb
      • dpkg-genbuildinfo../$pkg_$ver_$arch.buildinfo
      • dpkg-genchanges../$pkg_$ver_$arch.changes

Several of them already have an option to overwrite the directory and/or an be invoked from paths outside the normal build directory:

  • dpkg-source places the files in the current working directory by default, but you can give it an absolute path.
  • dpkg-deb can use an absolute path for its output file. It is invoked by dh_builddeb, which has the option --destdir=Verzeichnis.
  • dpkg-genbuildinfo has the -u$dir option.
  • dpkg-genchanges has the -u$dir option.

So for a first try for an out-of-tree build we can do it like this:

#/bin/sh
set -e -u

src="$PWD"
out="$HOME/my-repo"

# Manually build source with absolute path
dpkg-source --before-build .
(cd "$out" && dpkg-source --build "$src")

# For the rest use dpkg-buildpackage
DH_OPTIONS="--destdir=$out" \
dpkg-buildpackage \
  --buildinfo-option=-u"$out" \
  --changes-option=-u"$out" \
  -b --no-sign

# More work like
dpkg-source --aftere-build .
(cd "$out" && debsign *.changes)  # FIXME

This mostly works but fails for two reasons at the moment:

  1. The path for the .chagnes file is hard-coded in dpkg-buildpackage and cannot be changed.

  2. Using DH_OPTIONS also is not a good idea as the option --destdir is not unique for dh_builddeb: It is also used by dh_auto_install so files get installed in the wrong location.

TBC…

Written on May 3, 2020