generate.pl: Support building for multiple Debian releases

[zakame]

This adds generating Dockerfiles for each Perl version on multiple
Debian releases, such as for the current 5.30.x to support both Debian
10 (buster) and 9 (stretch). We also change the directory structure to
better indicate which Debian release it provides for.

Fixes #66 (after generating new Dockerfiles)

[Tekki]

Looks good, builds all the buster and stretch folders if I set 5.30 to

debian_releases:
  - buster
  - stretch

Shouldn't the default release in line 146 be set to 'buster'?

[zakame]

Shouldn't the default release in line 146 be set to 'buster'?

Good catch, thanks! This will also need updating the configs for older unsupported Perls to specify stretch explicitly (save for those already on jessie.)

[Tekki]

One more thing: If I delete all 5.030* folders and run the script then no '5.030.000-main' (without Debian release name) is built. What will the perl:5.30 tag on Dockerhub contain, stretch or buster?

[zakame]

perl:5.30 will default to buster. I'll post a PR on https://github.com/docker-library/official-images/blob/master/library/perl after regenerating Dockerfiles and adjust the tags.

[zakame]

Sorry for the delay, I'm seeing a failure on building perl:5.28-buster:

#   Failed test 'Trapped error when attempting to write to knobbled GDBM_File'
#   at t/fatal.t line 37.
#          got: '1'
#     expected: undef

#   Failed test 'expected error message from GDBM_File'
#   at t/fatal.t line 46.
#                   ''
#     doesn't match '(?^: at .*\bfatal\.t line \d+\.\n\z)'
# Looks like you failed 2 tests of 8.
../ext/GDBM_File/t/fatal.t ......................................... 
Dubious, test returned 2 (wstat 512, 0x200)
Failed 2/8 subtests 

Have yet to recheck perl:5.26-buster, but this seems like https://rt.perl.org/Public/Bug/Display.html?id=133295. Might need a Devel::PatchPerl update/PR for this to patch in Perl/perl5@0d9e812

[zakame]

https://metacpan.org/pod/Devel::PatchPerl#CAVEAT

Devel::PatchPerl is intended only to facilitate the building of perls, not to facilitate the testing of perls. This means that it will not patch failing tests in the perl testsuite.

So for this case, likely just need to copy in Perl/perl5@0d9e812 manually under the 5.2{6,8} directories.

[zakame]

I was hoping to get #68 done first, but local testing of all the new Dockerfiles for 5.26 through 5.30 seem OK for me now. I'll merge this and make a PR for Hub publication soon.

Thanks everyone!