.slimify-excludes break groff functionality

[paddy-hack]

The slim variants (at least buster-slim) break groff by excluding all files below /usr/share/groff/ in /etc/dpkg/dpkg.cfg.d/docker. A bit of digging led me to .slimify-excludes as the source for this.

I ran into the breakage when trying to convert manual pages for a project to HTML. All the groff macros are installed below /usr/share/groff/. Not installing them via the path-exclude completely breaks groff functionality. Even something like groff -man < inputfile works 😮

FTR, for a long time I also believed the content of this directory was not needed 🤦‍♂️

[tianon]

Hah, nice catch! I guess someone should probably update https://wiki.ubuntu.com/ReducingDiskFootprint#Drop_unnecessary_files too (which is where we got it from).

Are there things in /usr/share/groff that we should exclude? Perhaps a more specific subdirectory (or collection of subdirectories)?

[tianon]

Looking at https://packages.debian.org/buster/amd64/groff-base/filelist and https://packages.debian.org/buster/amd64/groff/filelist, I see a lot of things under font -- there's probably some of that that's related to why yours failed, but possibly some of it that's "extra" ?

We exclude things like locales, so some amount of breakage is somewhat intended with this image, but I guess it probably depends a lot on how common it is to have "groff" installed.

On my desktop system here, I've only got groff-base (accounting for ~1.8MB), and even in buildpack-deps:buster (which is a "batteries included" style of image, so quite large), there's nothing in /usr/share/groff, so perhaps it's safe to just not exclude.

[paddy-hack]

Eh, that Ubuntu wiki hasn't been modified since 2012-10-11.

The specific error I ran into was

$ cat sample.1 | groff
groff: can't find 'DESC' file
groff: fatal error: invalid device 'ps'

The groff command needs those /usr/share/groff/*/font/dev*/DESC files to be of any use. Depending on the input groff gets, it will need all other font files for a given device and if macros are given on the command line it needs a matching /usr/share/groff/*/tmac/*.tmac as well as any other *.tmac files that are referenced from it.

In short, excluding /usr/share/groff/* breaks the groff-base and groffpackages like completely if these are installed later by an unsuspecting user.

A quick apt-file search /usr/share/groff on my Devuan beowulf (nominally Debian buster) also shows noweb and tix-dev as putting one or two files there. I've just rebuilt my Devuan Docker images with the path-exclude removed. The images do not have a /usr/share/groff directory to begin with so there will not be any bloat of the base packages.

I'd remove the path-exclude as it only serves to knowingly break groff for no benefit to the Debian Docker images.