[PATCH 2 of 2 V2 mainline] format: introduce 'format.generaldelta=accept'

[Gregory Szorc]

On Tue, Nov 10, 2015 at 9:38 AM, Pierre-Yves David <
pierre-yves.david at ens-lyon.org> wrote:

>
>
> On 11/09/2015 01:24 PM, Matt Mackall wrote:
>
>> On Sun, 2015-11-08 at 12:00 -0500, Pierre-Yves David wrote:
>>
>>> # HG changeset patch
>>> # User Pierre-Yves David <pierre-yves.david at fb.com>
>>> # Date 1446479952 0
>>> #      Mon Nov 02 15:59:12 2015 +0000
>>> # Node ID 3feb562d4e83fcbb7c59fa79b5749aae45de9fb1
>>> # Parent  69c64edb25dd96a23564db5b23b8b432b343ec88
>>> # EXP-Topic generaldelta
>>> # Available At http://hg.netv6.net/marmoute-wip/mercurial/
>>> #              hg pull http://hg.netv6.net/marmoute-wip/mercurial/ -r
>>> 3feb562d4e83
>>> format: introduce 'format.generaldelta=accept'
>>>
>>
>>
>>   def gdconfig(ui):
>>>       """helper function to retrieve general delta setting
>>>
>>> -    The need for such function is triggered by a soon to come third
>>> possible
>>> -    value to the config option."""
>>> +    return (usegd, lazydelta) tuple
>>> +
>>> +    usegd: create new repository as general delta,
>>> +    lazydelta: do not redelta incoming bundle."""
>>> +    # the r'' is a trick to have checkconfig ignore the type
>>> mismatch
>>>       # experimental config: format.generaldelta
>>> -    return ui.configbool('format', 'generaldelta', False)
>>> +    if ui.config(r'format', 'generaldelta', '') == 'accept':
>>> +        return True, True
>>> +    # experimental config: format.generaldelta
>>> +    usegd = ui.configbool('format', 'generaldelta', False)
>>> +    return usegd, False
>>>
>>
>> Also, I don't think the logic here is nearly complex enough to warrant
>> a multi-value return. Let's just have two (nearly trivial) functions
>> defined next to each other.
>>
>
> Without this 1 config, 3 value approach, I;m not sure how to garantee
> proper transition to a new default without breaking people who explicitly
> opted in the existing option.
>
> Currently there is three possibilitie
>
> A) people who did not set the config
> B) people who set the config to True
> C) people who set the confid to False (huho, really?)
>
> The goal here is to get (A) from "no general delta" to (B) "general delta
> lazy base". In parallel, (B) says "general delta, no lazy base".
>
> If we move to one config, three values (no, accept, yes) we can change (A)
> without affecting (B) nor (C). If we move to two binary config, we get want
> we want for (A) but we regresse (B). They explicit config will match the
> new default, but they won't have anything set override the new lazybase
> one. Leading to delta not being recomputed (unlike before).
>
>
> So we either:
> 1) go for the 1 config 3 value options
> 2) say screw this, it was experimental (for 3 years…) we have no BC
> 3) find a way I missed
>
>
How about "throwing away" format.generaldelta and reinventing it as 2 new,
non-experimental config options. We can have an explicit setting of
format.generaldelta infer whatever makes sense. format.generaldelta is
marked as experimental after all. And, that config option is ambiguously
named if there exists a separate general delta option: "general delta what?"
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