Cython 3.0.0

[Julian Gilbey <julian@d-and-j.net>]

Dear all,

I am intending to package a new dependency of textdistance called
rapizfuzz (along with its dependencies jarowinkler and rapizfuzz-capi,
and including rapizfuzz-cpp and jarowinkler-cpp within the packages).
It's relatively low priority though (and I haven't filed ITPs yet).
But it needs cython 3.0.0alpha7 or later to be able to compile.

There is talk of moving cython 3.0.0 into beta in the not-too-distant
future: https://github.com/cython/cython/issues/4022  It does have
some breaking changes in comparison to cython 0.29.x.

I wonder what our strategy should be?  Here are three reasonable
approaches:

(1) Keep the existing cython package (source: cython, binaries:
cython3, cython-doc, cython3-dbg) and have a new package for the 3.*
releases.

Advantages:
* won't break lots of existing packages

Disadvantages:
* no obvious name for new package
* will end up with an old cython package over time that cannot be
  easily dropped
* will lead to confusion - what is the cython3 package, is it the new
  or old version of cython?

(2) Create a new cython0.29 package (source: cython0.29, binaries:
cython3-0.29, cython0.29-doc, cython3-0.29-dbg for example) to house
the "old" version, and the cython package becomes cython 3.0.0

Advantages:
* clear naming scheme
* those packages which "just work" with the new version of cython will
  not need to do anything to migrate
* allows the cython0.29 package to be dropped in time without needing
  lots of renaming once no packages still rely on it

Disadvantages:
* there are two packages to maintain instead of just one (cython0.29
  and cython)
* those packages which don't work with 3.0.0 will either need patching
  or their dependency will need to be changed to cython3-0.29

(3) Let the cython package become cython 3.0.0 once it is released.

Advantages:
* only one package to maintain
* keep at the cutting edge of cython development

Disadvantages
* may break lots of packages, requiring a lot of effort to patch them


I don't know how many packages in Debian would be broken by the move
to 3.0.0; that may be something worth exploring.  It may well be that
approach (2) makes most sense for the short term.

I imagine that this is unlikely to hit before the bookworm freeze, but
I wanted to flag it up now.

Best wishes,

   Julian