doc/todo/transient_pages.mdwn



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]].
It could also be used for an [[todo/alias_directive]].
--[[smcv]]

[[!template id=gitbranch branch=smcv/ready/transient author="[[smcv]]"]]
[[!template id=gitbranch branch=smcv/ready/transient-recentchanges author="[[smcv]]"]]
[[!template id=gitbranch branch=smcv/ready/transient-tag author="[[smcv]]"]]
[[!tag patch]]
I think this branch is now enough to be useful. It adds the following:
If the transient plugin is loaded, $srcdir/.ikiwiki/transient is added
as an underlay. I'm not sure whether this should be a plugin or core, so
I erred on the side of more plugins; I think it's "on the edge of the core",
like goto.
Pages in the transient underlay are automatically
deleted if a page of the same name is created in the srcdir (or an underlay
closer to the srcdir in stacking order).
With the additional ready/transient-tag branch,
tag enables transient, and if tag_autocreate_commit is set to 0
(default 1), autocreated tags are written to the transient underlay.
There is a regression test.
With the additional transient-autoindex branch,
autoindex uses autofiles. It also enables transient, and if
autoindex_commit is set to 0 (default 1), autoindexes are written to
the transient underlay. There is a regression test. However, this branch
is blocked by working out what the desired behaviour is, on
[[todo/autoindex_should_use_add__95__autofile]].

I wonder why this needs to be configurable? I suppose that gets back to
whether it makes sense to check these files in or not. The benefits of
checking them in:

You can edit them from the VCS, don't have to go into the web
interface. Of course, files from the underlays have a similar issue,
but does it make sense to make that wart larger?
You can know you can build the same site with nothing missing
even if you don't there enable autoindex or whatever. (Edge case.)


I'm not sure that that's a huge wart; you can always "edit by
overwriting". If you're running a local clone of the wiki on your laptop
or whatever, you have the underlays already, and can copy from there.
Tag and autoindex pages have rather simple source code anyway. --s


The benefit of using transient pages seems to just be avoiding commit
clutter? For files that are never committed, transient pages are a clear
win, but I wonder if adding configuration clutter just to avoid some
commit clutter is really worth it.


According to the last section of
[[todo/auto-create_tag_pages_according_to_a_template]], [[chrysn]] and
Eric both feel rather strongly that it should be possible to
not commit any tags; in [[plugins/autoindex/discussion]],
lollipopman and [[JoeRayhawk]] both requested the same for autoindex.
I made it configurable because, as you point out,
there are also reasons why it makes sense to check these
automatically-created files in. I'm neutral on this, personally.
If this is a point of contention, would you accept a branch that
just adds transient and uses it for [[plugins/recentchanges]],
which aren't checked in and never have been? I've split the
branch up in the hope that some of it can get merged.

I will be happy to merge transient-recentchanges when it's ready.
I see no obstacle to merging transient-tag either, and am not
really against using it for autoindex or aggregate either
once they get completed.
I just wanted to think through why configurability is needed.
--[[Joey]]

One potentially relevant point is that configuration clutter only
affects the site admin whereas commit clutter is part of the whole
wiki's history. --[[smcv]]


Anyway, the configurability
appears subtly broken; the default is only 1 if a new setup file is
generated. (Correction: It was not even the default then --[[Joey]])
With an existing setup file, the 'default' values in
getsetup don't take effect, so it will default to undef, which
is treated the same as 0. --[[Joey]]


Fixed in the branches, hopefully. (How disruptive would it be to have
defaults take effect whenever the setup file doesn't set a value, btw?
It seems pretty astonishing to have them work as they do at the moment.) --s


Well, note that default is not actually a documented field in
getsetup hooks at all! (It is used in IkiWiki.pm's own getsetup(), and
the concept may have leaked out into one or two plugins (comments,
transient)).
Running getsetup at plugin load time is something I have considered
doing. It would simplify some checkconfig hooks that just set hardcoded
defaults. Although since dying is part of the getsetup hook's API, it
could be problimaric.
--[[Joey]]


autoindex ignores pages in the transient underlay when deciding whether
to generate an index.
With the additional ready/transient-recentchanges branch, new recent
changes go in the transient underlay; I tested this manually.
Not done yet (in that branch, at least):


remove can't remove transient pages: this turns out to be harder than
I'd hoped, because I don't want to introduce a vulnerability in the
non-regular-file detection, so I'd rather defer that.

Hmm, I'd at least want that to be dealt with before this was used
by default for autoindex or tag. --[[Joey]]


I'll try to work out which of the checks are required for security
and which are just nice-to-have, but I'd appreciate any pointers
you could give. Note that my branch wasn't meant to enable either
by default, and now hopefully doesn't. --[[smcv]]


Transient tags that don't match any pages aren't deleted: I'm not sure
that that's a good idea anyway, though. Similarly, transient autoindexes
of directories that become empty aren't deleted.

Doesn't seem necessary, or really desirable to do that. --[[Joey]]


Good, that was my inclination too. --s


In my untested/transient branch, new aggregated files go in the
transient underlay too (they'll naturally migrate over time). I haven't
tested this yet, it's just a proof-of-concept.


I can confirm that the behavior of autoindex, at least, is excellent.
Haven't tried tag. Joey, can you merge transient and autoindex? --JoeRayhawk


Here are some other things I'd like to think about first: --[[Joey]]


There's a FIXME in autoindex.

Right, the extra logic for preventing autoindex pages from being
re-created. This is taking a while, so I'm going to leave out the
autoindex part for the moment. The FIXME is only relevant
because I tried to solve
[[todo/autoindex should use add__95__autofile]] first, but
strictly speaking, that's an orthogonal change. --s


Suggest making recentchanges unlink the transient page
first, and only unlink from the old location if it wasn't
in the transient location. Ok, it only saves 1 syscall :)

Is an unlink() really that expensive? But, OK, fixed in the
ready/transient-recentchanges branch. --s


It's not, but it's easy. :) --[[Joey]]


Similarly it's a bit worrying for performance that it
needs to pull in and use Cwd on every ikiwiki startup now.
I really don't see the need; wikistatedir should
mostly be absolute, and ikiwiki should not chdir in ways
that break it anyway.

The reason to make it absolute is that relative underlays
are interpreted as relative to the base underlay directory,
not the cwd, by add_underlay.
The updated ready/transient-only branch only loads Cwd if
the path is relative; an extra commit on branch
smcv/transient-relative goes behind add_underlay's
back to allow use of a cwd-relative underlay. Which direction
would you prefer?
I note in passing that [[plugins/autoindex]] and IkiWiki::Render
both need to use Cwd and File::Find on every refresh, so
there's only any point in avoiding Cwd for runs that don't
actually refresh, like simple uses of the CGI. --s


Oh, right, I'd forgotten about the horrificness of File::Find
that required a chdir for security. Ugh. Can we just avoid
it for those simple cases then? (demand-calculate wikistatedir)
--[[Joey]]


Unsure about the use of default_pageext in the change
hook. Is everything in the transientdir really going
to use that pageext? Would it be better to look up the
complete source filename?

I've updated ready/transient to do a more thorough GC by
using File::Find on the transient directory. This does
require File::Find and Cwd, but only when pages change,
and refresh loads both of those in that situation anyway.
At the moment everything in the transientdir will either
have the default_pageext or be internal, although I
did wonder whether to make [[plugins/contrib/album]]
viewer pages optionally be html, for better performance
when there's a very large number of photos. --s


Oh, ugh, more File::Find... Couldn't it just assume that the
transient page has the same extension as its replacement?
--[[Joey]]


An earlier version
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]]