Re: [elpa] externals/org 46da64c 4/6: org-persist.el: Fix `add-hook' priority argument

[Ihor Radchenko]

Hi Stefan,

Thanks for providing comments on this new feature!

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>  (add-hook 'kill-emacs-hook #'org-persist-gc)
>> -(add-hook 'kill-emacs-hook #'org-persist-write-all 1000)
>> +(add-hook 'kill-emacs-hook #'org-persist-write-all 100)
>
> The docstring also says:
>
>     Since nothing is \"always\" true, don't use 100 nor -100.
>
> 100 means that nothing will *ever* want to come later.  I.e. you claim
> to be the one and only function that will ever deserve to always be the
> last one on this hook, which is rather presumptuous, I think.

> AFAICT the only thing that actually matters is that it should come after
> `org-persist-gc`, so even just 0.01 would be good enough.  No need to
> get anywhere near 100 (tho it would make sense to leave room for other
> hooks that might need to come between `org-persist-gc` and
> `org-persist-write-all`).  Also, I'd recommend you add a comment
> explaining the constraints that were considered when choosing this depth
> (e.g "Make sure it comes after `org-persist-gc`").

The idea behind 100 is related to Org usage.  We save buffer-local
`org-element--cache' to files.  It needs to be done _after_ all the
possible changes in Org buffers are made.  If any hook changes an Org
buffer after `org-persist-write-all', the saved value will become
invalid.  I am not sure what can be a reasonable DEPTH value in such
case.  Can it be something like 1?  Looking through Emacs code base, I
can mostly see non-nil values as DEPTH argument.  So, maybe 90? 91?

Best,
Ihor