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]]