path: root/doc/todo/Resolve_native_reStructuredText_links_to_ikiwiki_pages.mdwn

NB! this page has been refactored, hopefully it is clearer now

I propose putting discussion posts somewhere in the vincity of
the secttion Individual reStructuredText Issues
Design
Goal
To be able to use rst as a first-class markup language in ikiwiki. I think
most believe this is almost impossible (ikiwiki is built around markdown).
Wikilinks
WikiLinks, first and foremost, are needed for a wiki. rST already allows
specifying absolue and relative URL links, and relative links can be used to
tie together wiki of rst documents.


Below are links to a small, working implementation for resolving
undefined rST references using ikiwiki's mechanism. This is Proposal 1
for rst WikiLinks.


Looking over at rST-using systems such as trac and MoinMoin; I think it
would be wiser to implement wikilinks by the :role: mechanism, together
with allowing a custom URL scheme to point to wiki links. This is
Proposal 2.
 This is a simple wiki page, with :wiki:`WikiLinks` and other_ links
 
 .. _other: wiki:wikilink

 We can get rid of the role part as well for WikiLinks::
 
     .. default-role:: wiki
 
 Enables `WikiLinks` but does not impact references such as ``other``
 This can be made the default for ikiwiki.



Benefits of using a :role: and a wiki: page/subpage URL scheme are
following:


rST documents taken out of the context (the wiki) will not fail as bad as
if they have lots of Proposal-1 links: They look just the same as valid
references, and you have to edit them all.
In contrast, should the :wiki: role disappear, one line is enough
to redefined it and silence all the warnings for the document:
 .. role:: wiki (title)



Implementation
Implementation of Proposal-2 wikilinks are in the branch
rst-wikilinks
    This is a simple wiki page, with :wiki:`WikiLinks` and |named| links
    
    .. |named| wiki:: Some Page

    We can get rid of the role part as well for WikiLinks::
    
        .. default-role:: wiki
    
    Enables `WikiLinks` but does not impact references such as ``named``
    This can be made the default for ikiwiki.

rst-wikilinks patch series includes changes at the end to use ikiwiki's
'htmllink' for the links (which is the only sane thing to do to work in all configurations).
This means a :wiki:Link should render just exactly like [[Link]] whether
the target exists or not.
On top of rst-wikilinks is rst-customize which adds two
power user features: Global (python) file to read in custom directives
(unsafe), and a wikifile as "header" file for all parsed .rst files (safe,
but disruptive since all .rst depend on it). Well, the customizations have
to be picked and chosen from this, but at least the global python file can
be very convenient.

Did you consider just including the global rst header text into an item
in the setup file? --[[Joey]]

Then rst_header would not be much different from the python script
rst_customize. rst_header is as safe as other files (though disruptive
as noted), so it should/could be a editable file in the Wiki. A Python
script of course can not be. There is nothing you can do in the
rst_header (that you sensibly would do, I think) that couldn't be done in
the Python script. rst_header has very limited use, but it is another
possibility, mainly for the user-editable aspect. --[[ulrik]]
(I foresaw only two things to be added to the rst_header: the default
role could be configured there (as with rst_wikirole), and if you have a
meta-role like :shortcut:, shortcuts could be defined there.)

I have some discussion on the docutils mailing list, the developers
of docutils seems to favor "Proposal 1", while I defend my ideas. They
want all users of ReST to use only the basic featureset to remain
compatible, of course. -- [[ulrik]]

Some rst-custom examples are here
Directives
Now Directives: As it is now, ikiwiki goes though (roughly):
filter, preprocess, htmlize, format as major stages of content
transformation. rST has major problems to work with any HTML that enters the
picture before it.


Formatting rST in htmlize (as is done now): Raw html can be escaped by
raw blocks:
 .. raw:: html

     \[[!inline and do stuff]]

(This can be simplified to alias the above as .. ikiwiki::)
This escape method works, if ikwiki can be persuaded to maintain the
indent when inserting html, so that it stays inside the raw block.


Formatting rST in filter (idea)


rST does not have to see any HTML (raw not needed)


rST directives can alias ikiwiki syntax:
..ikiwiki:: inline pages= ...


Using rST directives as ikiwiki directives can be complicated;
but rST directives allow a direct line (after :: on first line),
an option list, and a content block.





You've done a lot of work already, but ...
The filter approach seems much simpler than the other approaches
for users to understand, since they can just use identical ikiwiki
markup on rst pages as they would use anywhere else. This is very desirable
if the wiki allows rst in addition to mdwn, since then users don't have
to learn two completly different ways of doing wikilinks and directives.
I also wonder if even those familiar with rst would find entirely natural
the ways you've found to shoehorn in wikilinks, named wikilinks, and ikiwiki
directives?
Htmlize in filter avoids these problems. It also leaves open the possibility
that ikiwiki could become smarter about the rendering chain later, and learn
to use a better order for rst (ie, htmlize first). If that later happened,
the htmlize in filter hack could go away. --[[Joey]]


(BTW, the [[plugins/txt]] plugin already does html formatting
in filter, for similar reasons.) --[[Joey]]



Thank you for the comments! Forget the work, it's not so much.
I'd rank the :wiki: link addition pretty high, and the other changes way
behind that:
The :wiki:Wiki Link syntax is very appropriate as rst syntax
since it fits well with other uses of roles (notice that :RFC:822
inserts a link to RFC822 etc, and that the default role is a title role
(title of some work); thus very appropriate for medium-specific links like
wiki links. So I'd rank :wiki: links a worthwhile addition regardless of
outcome here, since it's a very rst-like alternative for those who wish to
use more rst-like syntax (and documents degrades better outside the wiki as
noted).

Unsure about the degredation argument. It will work some of
the time, but ikiwiki's [[ikiwiki/subpage/linkingrules]]
are sufficiently different from normal html relative link
rules that it often won't work. --[[Joey]]

With degradation I mean that if you take a file out of the wiki; the
links degrade to stylized text. If using default role, they degrade to
:title: which renders italicized text (which I find is exactly
appropriate). There is no way for them to degrade into links, except of
course if you reimplement the :wiki: role. You can also respecify
either the default role (the wikilink syntax) or the :wiki: role (the
:wiki:wikilink syntax) to any other markup, for example None.
--[[ulrik]]


The named link syntax (just like the :wiki: role) are inspired from
trac and a good fit, but only if the wiki is committed to
using only rst, which I don't think is the case.
The rst-customize changes are very useful for custom directive
installations (like the sourcecode directive, or shortcut roles I show
in the examples page), but there might be a way for the user to inject
docutils addons that I'm missing (one very ugly way would be to stick
them in sitecustomize.py which affects all Python programs).
With the presented changes, I already have a working RestructuredText
wiki, but I'm admitting that using .. raw:: html around all directives is
very ugly (I use few directives: inline, toggle, meta, tag, map)
On filter/htmlize: Well rst is clearly antisocial: It can't see HTML,
and ikiwiki directives are wrappend in paragraph tags. (For wikilinks
this is probably no problem). So the suggestion about .. ikiwiki: is
partly because it looks good in rst syntax, but also since it would emit
a div to wrap around the element instead of a paragraph.
I don't know if you mean that rst could be reordered to do htmlize before
other phases? rst must be before any preprocess hook to avoid seeing any
HTML.

One of my long term goals is to refactor all the code in ikiwiki
that manually runs the various stages of the render pipeline,
into one centralized place. Once that's done, that place can get
smart about what order to run the stages, and use a different
order for rst. --[[Joey]]

If I'm thinking right, processing to HTML already in filter means any
processing in scan can be reused directly (or skipped if it's legal to
emit 'add_link' in filter.)
-- [[ulrik]]





Seems it could be, yes. --[[Joey]]

It is not clear how we can work around reST wrapping directives with
paragraph tags. Also, some escaping of xml characters & <> might
happen, but I can't imagine right now what breakage can come from that.
-- [[ulrik]]




Implementation
Preserving indents in the preprocessor are in branch pproc-indent
(These simple patches come with a warning: Those are the first lines of
Perl I've ever written!)

This seems like a good idea, since it solves issues for eg, indented
directives in mdwn as well. But, looking at the diff, I see a clear bug:


                          return "[[!$command <span class=\"error\">".





                          $result = "[[!$command <span class=\"error\">".



That makes it go on and parse an infinitely nested directive chain, instead
of immediatly throwing an error.
Also, it seems that the "indent" matching in the regexps may be too broad,
wouldn't it also match whitespace before a directive that was not at the beginning
of a line, and treat it as an indent? With some bad luck, that could cause mdwn
to put the indented output in a pre block. --[[Joey]]

You are probably right about the bug. I'm not quite sure what the nested
directives examples looks like, but I must have overlooked how the
recursion counter works; I thought simply changing if to elif the next
few lines would solve that. I'm sorry for that!
We don't have to change the $handle function at all, if it is possible
to do the indent substitution all in one line instead of passing it to
handle, I don't know if it is possible to turn:
 $content =~ s{$regex}{$handle->($1, $2, $3, $4, $5)}eg;

into
 $content =~ s{$regex}{s/^/$1/gm{$handle->($2, $3, $4, $5)}}eg;

Well, no idea how that would be expressed, but I mean, replace the indent
directly in $handle's return value.

Yes, in effect just indent($1, handle->($2,$,4)) --[[Joey]]

The indent-catching regex is wrong in the way you mention, it has been
nagigng my mind a bit as well; I think matching start of line + spaces
and tabs is the only thing we want.
-- [[ulrik]]

Well, seems you want to match the indent at the start of the line containing
the directive, even if the directive does not start the line. That would
be quite hard to make a regexp do, though. --[[Joey]]

I wasted a long time getting the simpler indent($1, handle->($2,$,4)) to
work (remember, I don't know perl at all). Somehow $1 does not arrive, I
made a simple testcase that worked, and I conclude something inside $handle
results in the value of $1 not arriving as it should!
Anyway, instead a very simple incremental patch is in pproc-indent
where the indentation regex is (^[ \t]+|) instead, which seems to work
very well (and the regex is multiline now as well). I'm happy to rebase the
changes if you want or you can just squash the four patches 1+3 => 1+1
-- [[ulrik]]


Discussion
I guess you (or someone) has been through this before and knows why it
simply won't work. But I hoped there was something original in the above;
and I know there are wiki installations where rST works. --ulrik
Individual reStructuredText Issues


We resolve rST links without definition, we don't help resolving defined
relative links, so we don't support specifying link name and target
separately.

Resolved by |replacement| links with the wiki:: directive.



A first implementation: Resolving unmatched links
I have a working minimal implementation letting the rst renderer resolve
undefined native rST links to ikiwiki pages. I have posted it as one patch at:
Preview commit: http://github.com/engla/ikiwiki/commit/486fd79e520da1d462f00f40e7a90ab07e9c6fdf

Repository: git://github.com/engla/ikiwiki.git
Design issues of the patch:
The page is rST-parsed once in 'scan' and once in 'htmlize' (the first to generate backlinks). Can the parse output be safely reused?

The page content fed to htmlize may be different than that fed to scan,
as directives can change the content. If you cached the input and output
at scan time, you could reuse the cached data at htmlize time for inputs
that are the same -- but that could be a very big cache! --[[Joey]]



I would propose using a simple heuristic: If you see [[ anywhere on the
page, don't cache it. It would be an effective cache for pure-rst wikis
(without any ikiwiki directives or wikilinks).
However, I think that if the cache does not work for a big load, it should
not work at all; small loads are small so they don't matter. --ulrik