Source download with custom `DLAGENTS` fails in clean chroot

In some cases, sources need to be downloaded with a custom downloader, usually curl or wget. This can be done by specifying DLAGENTS (e.g. DLAGENTS=("https::/usr/bin/wget -U "Mozilla" %u")). For this to work, the called command (wget in the example) has to be available.

However, sources are downloaded outside the chroot. This means that the command used in DLAGENTS is the one on the host system - where it has to be installed. curl sort of works since it's a dependency of pacman (and therefore in base), but wget just fails.
This issue happens with the genymotion package:

==> Retrieving sources...
  -> Found genymotion.desktop
==> ERROR: The download program wget is not installed.
    Aborting...
==> ERROR: Could not download sources.

Steps to reproduce

  1. Uninstall wget or set up system without wget installed.
  2. Build genymotion in a clean chroot.
  3. Build fails while downloading sources due to wget not being installed.

Analysis

wget is declared in makedepends, so it works when using makepkg -s as it first installs dependencies, and only afterwards downloads the sources.
The relevant code in devtools is src/makechrootpkg.in#L250. devtools does not use makepkg -s when downloading and verifying the sources.

Possible solutions

The easy workaround is to just manually install wget or the missing software on the host system. Not pretty, but works.
Of course, devtools must not install programs (wget) on the host, so using makepkg -s to automate this is not feasible.

The proper solution likely involves chroots in some form to first install the dependencies and then download the sources, like makepkg does. The script in DLAGENTS has complete access to the host system. Putting the download into the chroot means that the sources aren't automatically saved on the host system - though devtools might elect to copy the sources instead.


If you have questions or can't reproduce the issue, please let me know. Suggestions to solve this issue are always welcome.
-- Vekhir

Edited by Vekhir --