[buildd-tools-devel] Bug#766939: wanna-build: Wanna-build considers alternatives, but buildds don't, causing futile builds

[Wookey]

Package: wanna-build
Severity: normal

Sometimes packages go round and round on the builds, trying to be
built repeatedly, because wanna-build thinks that the build-deps are
availbale, but when sbuild tries the build it finds them
unsatisfiable.

This appears to happen when Build-Depends has alternatives. It seems
that wanna-build considers it OK if any of the alternatives are
available, even though buildds only take the first option.

My current example is openmeeg. This build-deps on 
libtiff4-dev | libtiff-dev

and has tried to build 33 times in the last 8 days, 
https://buildd.debian.org/status/logs.php?pkg=openmeeg&ver=2.0.0.dfsg-5.1&arch=arm64

always failing with:

Install openmeeg build dependencies (apt-based resolver)
--------------------------------------------------------
...
The following packages have unmet dependencies:
 sbuild-build-depends-openmeeg-dummy : Depends: libtiff4-dev but it is not installable
E: Unable to correct problems, you have held broken packages.
apt-get failed.
-------------------

Surely wanna-build should be setting this to BD-uninstallable, not needs-build?

I've seen the same problem with packages build-depping on emacs23 |
emacsen (emacs23 has never been available on arm64).
https://buildd.debian.org/status/fetch.php?pkg=doxymacs&arch=arm64&ver=1.8.0-6&stamp=1412954802


The following packages have unmet dependencies:
 sbuild-build-depends-doxymacs-dummy : Depends: emacs23 but it is not installable
E: Unable to correct problems, you have held broken packages.
apt-get failed.

The build-deps are: emacs23 | emacsen

Is this a wanna-build bug?