ikiwiki/doc/todo/syntax_highlighting.mdwn

There's been a lot of work on contrib syntax highlighting plugins. One should be
picked and added to ikiwiki core.

We want to support both converting whole source files into wiki
pages, as well as doing syntax highlighting as a preprocessor directive 
(which is either passed the text, or reads it from a file). But,
the [[ikiwiki/directive/format]] directive makes this easy enough to 
do if the plugin only supports whole source files. So, syntax plugins
do no really need their own preprocessor directive, unless it makes
things easier for the user.

## The big list of possibilities

* [[plugins/contrib/highlightcode]] uses [[!cpan Syntax::Highlight::Engine::Kate]],
  operates on whole source files only, has a few bugs (see
  [here](http://u32.net/Highlight_Code_Plugin/), and needs to be updated to
  support [[bugs/multiple_pages_with_same_name]]. (Currently a 404 :-( )
* [[!cpan IkiWiki-Plugin-syntax]] only operates as a directive.
  Interestingly, it supports multiple highlighting backends, including Kate
  and Vim.
* [[plugins/contrib/syntax]] only operates as a directive
  ([[not_on_source_code_files|automatic_use_of_syntax_plugin_on_source_code_files]]),
  and uses [[!cpan Text::VimColor]].
* [[plugins/contrib/sourcehighlight]] uses source-highlight, and operates on
  whole source files only. Needs to be updated to
  support [[bugs/multiple_pages_with_same_name]].
* [[sourcecode|todo/automatic_use_of_syntax_plugin_on_source_code_files/discussion]]
  also uses source-highlight, and operates on whole source files.
  Updated to work with the fix for [[bugs/multiple_pages_with_same_name]].  Untested with files with no extension, e.g. `Makefile`.
* [[users/jasonblevins]]'s code plugin uses source-highlight, and supports both
  while file and directive use.

* [hlsimple](http://pivot.cs.unb.ca/git/?p=ikiplugins.git;a=blob_plain;f=IkiWiki/Plugin/hlsimple.pm;hb=HEAD) is a wrapper for the the perl module [[!cpan Syntax::Highlight::Engine::Simple]].  This is pure perl, pretty simple, uses css. It ought to be pretty fast (according to the author, and just because it is not external).
On the other hand, there are not many predefined languages yet.  Defining language syntaxes is about as much 
work as source-highlight, but in perl.  I plan to package the base module for debian. Perhaps after the author 
releases the 5 or 6 language definitions he has running on his web site, it might be suitable for inclusion in ikiwiki. [[DavidBremner]]

## General problems / requirements

* Using non-perl syntax highlighting backends is slower. All things equal,
  I'd prefer either using a perl module, or a multiple-backend solution that
  can use a perl module as one option. (Or, if there's a great highlighter
  python module, we could use an external plugin..)

  Of course, some perl modules are also rather slow.. Kate, for example
  can only process about 33 lines of C code, or 14 lines of
  debian/changelog per second. That's **30 times slower than markdown**!

  By comparison, source-highlight can do about 5000 lines of C code per
  second... And launching the program 100 times on an empty file takes about
  5 seconds, which isn't bad. And, it has a C++ library, which it
  seems likely perl bindings could be written for, to eliminate 
  even that overhead.
  > [highlight](http://www.andre-simon.de) has similar features to source-highlight, and swig bindings
  > that should make it trivial in principle to call from perl.  I like highlight a bit better because 
  > it has a pass-through feature that I find very useful.  My memory is unfortunately a bit fuzzy as to how
  > well the swig bindings work. [[DavidBremner]]


* Engines that already support a wide variety of file types are of
  course preferred. If the engine doesn't support a particular type
  of file, it could fall back to doing something simple like
  adding line numbers. (IkiWiki-Plugin-syntax does this.)
* XHTML output.
* Emitting html that uses CSS to control the display is preferred,
  since it allows for easy user customization. (Engine::Simple does
  this; Kate can be configured to do it; source-highlight can be 
  made to do it via the switches `--css /dev/null --no-doc`)
* Nothing seems to support 
  [[wiki-formatted_comments|wiki-formatted_comments_with_syntax_plugin]]
  inside source files. Doing this probably means post-processing the 
  results of the highlighting engine, to find places where it's highlighted
  comments, and then running them through the ikiwiki rendering pipeline.
  This seems fairly doable with [[!cpan Syntax::Highlight::Engine::Kate]],
  at least.
* The whole-file plugins tend to have a problem that things that look like
  wikilinks in the source code get munged into links by ikiwiki, which can
  have confusing results. Similar problem with preprocessor directives.
  One approach that's also been requested for eg,
  [[plugins/contrib/mediawiki]] is to allow controlling which linkification
  types a page type can have on it.

  > The previous two points seem to be related.  One thought: instead of
  > getting the source from the `content` parameter, the plugin could
  > re-load the page source.  That would stop directives/links from
  > being processed in the source.  As noted above, comments
  > could then be parsed for directives/links later.
  >
  > Would it be worth adding a `nodirectives` option when registering
  > an htmlize hook that switches off directive and link processing before
  > generating the html for a page?

* The whole-file plugins all get confused if there is a `foo.c` and a `foo.h`.
  This is trivially fixable now by passing the keepextension option when
  registering the htmlize hooks, though. There's also a noextension option
  that should handle the
  case of source files with names that do not contain an extension (ie,
  "Makefile") -- in this case you just register the while filename
  in the htmlize hook.
* Whole-file plugins register a bunch of htmlize hooks. The wacky thing
  about it is that, when creating a new page, you can then pick "c" or
  "h" or "pl" etc from the dropdown that normally has "Markdown" etc in it.
  Is this a bug, or a feature? Even if a feature, plugins with many
  extensions make the dropdown unusable.. 

  Perhaps the thing to do here is to use the new `longname` parameter to
  the format hook, to give them all names that will group together at or
  near the end of the list. Ie: "Syntax: perl", "Syntax: C", etc.

## format directive and comments

Hmm, the [[ikiwiki/directive/format]] directive would also allow comments
inside source files to have mdwn embedded in them, without making the use
of mdwn a special case, or needing to postprocess the syntax highlighter
output to find comments.

	/* \[[!format mdwn """

	This is a comment in my C file. You can use mdwn in here.

	"""]] */

Note that this assumes that directives are expanded in source files,
which has its own set of problems.