Build a debugging version of Perl

[waterkip]

Create a debugging version of Perl with gdb installed so one can take an
exact copy of the image with all the symbol tables etc etc.

[zakame]

Thanks @waterkip! A debug build certainly has its uses, though just not sure if we'd want a new variant for this published on the Docker Hub, as IIRC other language images don't publish debug variants either; @tianon what do you think?

If ever, we'd also want to update the README here and https://github.com/docker-library/docs/tree/master/perl.

[tianon]

Conceptually I think this is OK, but I have a couple practical concerns with this. The first is that there are already quite a few tags on https://hub.docker.com/_/perl, and this will effectively double the number. For a real-world example of how awful this can get, see https://hub.docker.com/_/php or https://hub.docker.com/_/openjdk.

My second concern is the build time/load since we're build all these releases from source and this will effectively double that (which isn't nearly as big of a concern as the optics/usability for users, but still something to consider).

[zakame]

@tianon perhaps we could retain debug Dockerfiles here only in this repo and just point to it from the docs as something people can "opt in" and build locally?

It could also be a step towards providing dev/RC releases as well; they could go with debug by default.

[waterkip]

@zakame I was thinking a bit along the same line.

If docker hub allows subname spaces, you could also opt for another option. Gitlab's registry allows namespaces as such: project:tag, project/subnamespace:tag, project/subnamespace/subsubnamespace:tag

We could then implement all the debug builds into their own namespace, perl/debug. Less clutter from a user perspective. Or maybe call it perl/devel if you also want development releases.

[tianon]

Both of those options sound really reasonable to me -- do y'all already have control of the perl namespace on Docker Hub? (that seems like a great place for these if so; if not, the best I can offer is contacting Docker's Support and asking real nice 😅)

[zakame]

@tianon tried creating perl org but it is a reserved name in Docker Hub 😅

[tianon]

I think it's taken, but there don't appear to be any repos, so I think it's just a squatter and Docker support might either take pity on you, get in touch with the owner on your behalf, or connect you with the owner so you can discuss (they've done things like that previously but I haven't done so nor talked to anyone who's done so recently so I don't know if that's still a thing they're willing to discuss or entertain).

[mohawk2]

@tianon Sounds like the time for you to ask them real nice? ;-)

(it seems this PR now clashes, that would need resolving)