Deploying registrar configs in a BC safe way

[Augie Fackler]

> On Oct 25, 2017, at 13:00, Boris Feld <boris.feld at octobus.net> wrote:
> 
> On Wed, 2017-10-25 at 09:48 -0700, Durham Goode wrote:
>> 
>> On 10/25/17 5:48 AM, Augie Fackler wrote:
>>> 
>>>> On Oct 25, 2017, at 07:51, Yuya Nishihara <yuya at tcha.org> wrote:
>>>> 
>>>> On Tue, 24 Oct 2017 18:49:50 -0700, Gregory Szorc wrote:
>>>>>> On Oct 24, 2017, at 10:25, Durham Goode <durham at fb.com>
>>>>>> wrote:
>>>>>> 
>>>>>> I've been trying to update our extensions to support the new
>>>>>> registrar class, and one thing I've noticed is that it's not
>>>>>> really possible to have code that works with old versions of
>>>>>> mercurial and new versions of mercurial at the same time,
>>>>>> without having devel warnings. I can easily stub out the
>>>>>> registration logic if the registrar module doesn't exist, but
>>>>>> I can't leave the default values on the actual config
>>>>>> accessor lines, which old mercurial versions would need.
>>>> 
>>>> I made all extension-specific configs "dynamic", and add explicit
>>>> defaults
>>>> to ui.config*() calls instead.
>>>> 
>>>> https://urldefense.proofpoint.com/v2/url?u=https-
>>>> 3A__bitbucket.org_yuja_hgext-
>>>> 2Dtextful_commits_1f284a246abb&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&
>>>> r=nuarHzhP1wi1T9iURRCj1A&m=lR7l4BfqDK6q7Iea-79Q-
>>>> h1teNA3oQLKKh7QiqDoA4M&s=2ycQgVlPv5dGVFQUeMGUTS1h8KHBikUl11j9FoGk
>>>> 7m4&e=
> 
> Using dynamicdefault when a custom default is needed seems like an
> acceptable workaround for extension supporting older codebase. The
> calls to ui.configxxx do not need to be updated.
> 
> We did the same thing in Evolve and topic. It worked well for us.
> 
> https://www.mercurial-scm.org/repo/evolve/rev/461c9d940519#l2.26

Okay. Could you add that information to the UpgradeNotes wiki page?
> 
>>>> 
>>>>>> I tried to think of some way to fix this, like by leaving the
>>>>>> defaults on the config access line, but ignoring it somehow,
>>>>>> but that sounds funky. Thoughts on how to fix this?
>>>>> 
>>>>> How about making registrar instances on extensions have
>>>>> different behavior from core? e.g.
>>>>> 
>>>>> * No devel warnings for e.g. missing default values for a few
>>>>> releases
>>>>> * Arguments to control which devel warnings are issued
>>>> 
>>>> Or,
>>>> 
>>>> * No devel warnings for the "ui.config()" default matching the
>>>> "configitem"
>>>>  default, which should be harmless
>>> 
>>> That seems like a good transitional step, I like it. What do others
>>> think?
>>> 
> 
> It seems harmless and helpful to extensions authors. As long as we
> clean it for 4.5.

That works for me. Could you write up a patch? You know that part of the code better than the rest of us.

Thanks!
Augie