ikiwiki/doc/todo/transient_in-memory_pages.mdwn

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On [[todo/auto-create_tag_pages_according_to_a_template]], [[chrysn]]
suggests:
> Instead of creating a file that gets checked in into the RCS, the
> source files could be left out and the output files be written as
> long as there is no physical source file (think of a virtual underlay).
> Something similar would be required to implement alias directive,
> which couldn't be easily done by writing to the RCS as the page's
> contents can change depending on which other pages claim it as an alias.
`add_autofile` could be adapted to do this, or a similar API could be
added.
This would also be useful for autoindex, as suggested on
[[plugins/autoindex/discussion]]. I'd also like to use it for
[[plugins/contrib/album]].
One refinement I'd suggest is that if the transient page is edited,
its transient contents are evaluated and used as the initial
content for the edit box; after that, it'd become a static page. --[[smcv]]
--------------------------
[[!template id=gitbranch branch=smcv/transient author="[[smcv]]"]]
[[!tag patch]]
I had a look at implementing this. It turns out to be harder than I thought
to have purely in-memory pages (several plugins want to be able to access the
source file as a file), but I did get this proof-of-concept branch
to write tag and autoindex pages into an underlay.
This loses the ability to delete the auto-created pages (although they don't
clutter up git this way, at least), and a lot of the code in autoindex is
probably now redundant, so this is probably not quite ready for merge, but
I'd welcome opinions.
Usage: set `tag_underlay` and/or `autoindex_underlay` to an absolute path,
which you must create beforehand. I suggest *srcdir* + `/.ikiwiki/transient`.
Refinements that could be made if this approach seems reasonable:
* make these options boolean, and have the path always be `.ikiwiki/transient`
* improve the `remove` plugin so it also deletes from this special underlay
>> Perhaps it should be something more generic, so that other plugins could use it (such as "album" mentioned above).
>> The `.ikiwiki/transient` would suit this, but instead of saying "tag_underlay" or "autoindex_underlay" have "use_transient_underlay" or something like that?
>> Or to make it more flexible, have just one option "transient_underlay" which is set to an absolute path, and if it is set, then one is using a transient-underlay.
>> --[[KathrynAndersen]]
>>> What I had in mind was more like `tag_autocreate_transient => 1` or
>>> `autoindex_transient => 1`; you might conceivably want tags to be
>>> checked in but autoindices to be transient, and it's fine for each
>>> plugin to make its own decision. Going from that to one boolean
>>> (or just always-transient if people don't think that's too
>>> astonishing) would be trivial, though.
>>>
>>> I don't think relocating the transient underlay really makes sense,
>>> except for prototyping: you only want one, and `.ikiwiki` is as good
>>> a place as any (ikiwiki already needs to be able to write there).
>>>
>>> For [[plugins/contrib/album]] I think I'd just make the photo viewer
>>> pages always-transient - you can always make a transient page
>>> permanent by editing it, after all.
>>>
>>> Do you think this approach has enough potential that I should
>>> continue to hack on it? Any thoughts on the implementation? --[[smcv]]
>>>> Ah, now I understand what you're getting at. Yes, it makes sense to put transient pages under `.ikiwiki`.
>>>> I haven't looked at the code, but I'd be interested in seeing whether it's generic enough to be used by other plugins (such as `album`) without too much fuss.
>>>> The idea of a transient underlay gives us a desirable feature for free: that if someone edits the transient page, it is made permanent and added to the repository.
>>>>
>>>> I think the tricky thing with removing these transient underlay pages is the question of how to prevent whatever auto-generated the pages in the first place from generating them again - or, conversely, how to force whatever auto-generated those pages to regenerate them if you've changed your mind.
>>>> I think you'd need something similar to `will_render` so that transient pages would be automatically removed if whatever auto-generated them is no longer around.
>>>> -- [[KathrynAndersen]]