Re: [FR] Make notion of "modification time" configurable during publishing

[Ihor Radchenko <yantar92@posteo.net>]

Suhail Singh <suhailsingh247@gmail.com> writes:

> Ihor Radchenko writes:
>
>> But do you actually use one but not other in practice?
>
> As in, could users have a preference for one vs the other in practice?
> Yes, since the choice isn't without consequence, it's conceivable
> (generally speaking) that some would prefer one over the other. FWIW, in
> my specific case, I use CommitDate, but I am not convinced it's "the
> right thing" in all situations.
>
> Not having conducted a survey, I also cannot comment on the frequency
> with which users have a desired preference for one vs the other. I am
> also not aware of general rules where users would necessarily prefer one
> over the other, but it's possible they may exist. My point was to simply
> point out that there is more than one interpretation of
> "vc-modification-time".

I see your point. Although, from the point of view of Org development,
we do not want to add features nobody practically use. Such features add
burden upon maintainers and do not practically benefit users. So, I am
inclined to reuse the existing approach and only add more granularity if
users ask for it.

>> It will only work for files without includes and force us to use
>> exactly the same hash algorithm.
>
> I don't follow. I was stating that the concept of a "file hash" could be
> obtained in more than way. I.e., in addition to it being calculated "by
> hand" it would also be possible to query an oracle (the VCS in this
> case) for it. This is distinct and orthogonal from the decision of how a
> "file with includes" is handled.

Sure. But the way "file hash" is calculated should be consistent. The
way Emacs calculates hash is different from git. So, supporting Emacs
and git ways means more code (not a good thing unless necessary). We
should thus prefer Emacs API to calculate hash.

> If I understand you correctly, the logic you have in mind, would be
> something like this:
>
> - during publish, compare the file hash of the file being published as
>   well as all included files
> - if the values for all are the same as in the cache, don't publish (if
>   user has signalled such intent via the equivalent of
>   org-publish-use-timestamps-flag)
> - if the value of any one is different, re-publish and update cache with
>   the updated file hashes
>
> It doesn't matter how the specific file hash is obtained, as long as the
> mechanism is being used consistently and the file hash of the included
> files are also being consulted in an appropriate way.

Yup, you are correct.

Now, to practice - let's start from updating ox-publish to use text hash
to decide about re-publishing. I will put it into my todo list, but
patches are more than welcome (my todo list is rather long). The
function to start looking into is `org-publish-cache-file-needs-publishing'.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
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