[DRE-maint] Bug#860747: dh_ruby: please inject versioned dependency on ruby metapackage

[Aaron M. Ucko]

Package: gem2deb
Version: 0.33.1
Severity: normal

Please have compiled Ruby extensions depend on compatible versions of
the ruby metapackage; for instance, an extension built only for 2.3
would depend on ruby (>= 2.3), ruby (<< 2.4), and an extension built
for both 2.3 and 2.4 would depend on ruby (>= 2.3), ruby (<< 2.5).
(Python packaging settled on an analogous approach some time ago.)
Ideally, this dependency would go to a dedicated ${ruby:Depends}
substvar, but adding it to ${misc:Depends} would allow for much faster
adoption.

As it stands, we can get situations like #860512, in which the m68k
build of telegram-desktop failed because ruby 2.3 wound up paired with
a ruby-fast-xs installation that only covered 2.2.  (The 0.8.0-3+b2
m68k binNMU was intended to add 2.3 support, but accidentally picked
up old metapackages.)  With an explicit versioned dependency in place,
generic automated tools would have caught this problem.

Thanks!

-- 
Aaron M. Ucko, KB1CJC (amu at alum.mit.edu, ucko at debian.org)
http://www.mit.edu/~amu/ | http://stuff.mit.edu/cgi/finger/?amu@monk.mit.edu