[R-pkg-team] Bug#1089197: dh-r: Stop generating Depends/Suggests/Recommends from the apt cache

[Philip Rinn]

[please keep me and the bug in cc]

Hi,

during the effort to reproduce Debian binary packages distributed via 
deb.debian.org (see https://reproduce.debian.net) it turned out that 
many/most/all R package couldn't be reproduced as some 
Depends/Suggests/Recommends where missing.

After digging it bit - the missing build-dependency on apt was 
unfortunately just a red herring -  it turns out, the problem is that 
check_real_version_of_package() in dh/R.pm[1] uses 'grep-aptavail' and 
thus the result depends on the state of the apt cache.
As parse_depends() (in dh/R.pm) calls check_real_version_of_package() to 
build Depends/Suggests/Recommend they depend on the status of the apt 
cache as well.

While this seems to be a quite elegant solution to the problem of 
mapping R package names to Debian package names, it turns out to be 
quite hard to reproduce the state of the apt cache for a given point in 
time.

Jochen reminded me of the solution dh-python chose [2] for that problem 
and I do think a (simplified) version of that would work for R packages 
as well.

The main idea is to have a mapping table embedded in dh-r which can be 
overrode on package level.

mapping table would basically be

<R package name> <corresponding Debian package name>
knitr r-cran-knir
ggplot2 r-cran-ggplot2
reshape2 r-cran-reshape2
...

containing a mapping for all packages in Debian unstable at the time of 
the dh-r upload.

This would of course mean that we'd need to keep that list moderately 
updated in the dh-r package.

As we can't guarantee that, we need the possibility to place a file in 
debian/ to amend/override the mapping table dh-r provides. (We could of 
course have a helper script creates that file for us.)


I'm quite sure, I miss some details here and I do entirely miss the 
context of why the current approach was chosen, but I hope, we can start 
a discussion on how to make it possible to reproduce R packages going 
forward.

Best
Philip


[1] 
https://salsa.debian.org/r-pkg-team/dh-r/-/blob/5d6dc04ba4f1f1b5db4bfaecc0e00893e46e5c72/dh/R.pm#L147-L170

[2] 
https://salsa.debian.org/python-team/tools/dh-python/-/blob/master/pydist/README.PyDist
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