Dropping Support for Python 2.6

[Gregory Szorc]

Remind me: does CentOS 6 also have access? I know I was using the IUS
repositories (https://ius.io/) to get 2.7 on both RHEL 6 and CentOS 6. I
just can't remember why I used them over SCL.

I think the fear people have with installing a python2.7 package is that it
puts things in /usr and PATH and could potentially interfere with other
parts of system operation. e.g. scripts that look for `python2.7` and
`python2.6` and use the first available could switch to 2.7 once the
package is installed. That's arguably a good thing. But if you have some
machine collecting dust, sometimes keeping things the way they are is the
safest/best outcome. So a minimally invasive, self-contained Mercurial
package could be desirable.

(For the record, I'd like to hear from users still on 2.6 so we can make an
informed decision about how to support these distros.)

On Thu, Apr 27, 2017 at 12:26 PM, Alex Gaynor <agaynor at mozilla.com> wrote:

> FWIW, RHEL 6 supports SCL (Software Collection Libraries) so it's possible
> to get a Python2.7 _from Red Hat_.
>
> Alex
>
> On Thu, Apr 27, 2017 at 3:23 PM, Gregory Szorc <gregory.szorc at gmail.com>
> wrote:
>
>> I think the time has come to make a decision about dropping support for
>> Python 2.6.
>>
>> In [1], we already decided that supporting 2.6 on Windows made no sense.
>> While I don't think we ever wrote a patch, support for 2.6 on Windows is
>> effectively gone.
>>
>> Also in that thread, Facebook said they will stop caring about Python 2.6
>> no later than 2017-04-30. Facebook runs some internal CI that helps flush
>> out upstream bugs. And once they drop 2.6 support on their end, I imagine
>> it will be more difficult for them to contribute certain things to core
>> because they require 2.7. I'd like to not inconvenience one of our largest
>> source of contributions.
>>
>> In [2], Augie seemed to indicate that he supports 4.2 or 4.3 being the
>> last release that supports Python 2.6.
>>
>> At this point in time, Python 2.6 is a constant thorn in our side to
>> support. It is hampering efforts to modernize the code. This is making the
>> Python 3 port more difficult than it could be. There are bugs and
>> workarounds for 2.6 that are just plain ugly. Furthermore, Python 2.6 isn't
>> a secure execution platform. It doesn't support modern TLS versions and
>> features. Upstream CPython support has been dead since 2013. Only long term
>> support distros like RedHat 6 continue to run and support Python 2.6.
>>
>> I'd like to formally propose making Mercurial 4.2 (the release scheduled
>> for May 1) the last release that supports Python 2.6.
>>
>> I anticipate that dropping 2.6 support will only inconvenience users on
>> certain, legacy Linux distributions and other *NIX operating systems in a
>> similar boat. Of these, I'm willing to wager that we really only care about
>> RHEL 6 and variants (like CentOS 6). If these users will be significantly
>> inconvenienced by lack of Python 2.6 support, I propose we make it easy to
>> produce a self-contained Mercurial RPM containing a bundled Python 2.7.
>> e.g. `make docker-centos6`. The Python within would be installed to e.g.
>> /usr/lib/mercurial and wouldn't interfere with system operation: only
>> shebangs in `hg` and other Mercurial-related executables would reference
>> it. If the *capability* of producing those RPMs from a source distribution
>> is not enough, we can consider hosting those RPMs on
>> www.mercurial-scm.org for direct download (read: we wouldn't operate a
>> full RPM repository with metadata, just raw files).
>>
>> [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017
>> -March/094837.html
>> [2] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017
>> -April/097074.html
>>
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>>
>>
>
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