doc/todo/nested_preprocessor_directives.mdwn



Ikiwiki's preprocessor parser cannot deal with arbitrary nested preprocesor
directives. It's possible to nest a directive with single quoted values
inside a triple-quoted value of a directive, but that's all.
It's not possible to unambiguously parse nested quotes, so to support
nesting, a new syntax would be needed. Maybe something xml-like?

You can, however, unambiguously parse nested square brackets, and I think
that would solve the problem, as long as you never allow the contents of a
directive to contain a partial directive, which seems reasonable to me.
For example, I think you can unambiguously parse the following:
\[[!if test="enabled(template) and templates/foo" then="""
[[!template id=foo content="""Flying Purple People Eater"""]]
"""]]

--[[JoshTriplett]]


Yes it's definitely possible to do something like that. I'm not 100%
sure if it can be done in perl regexp or needs a real recursive descent
parser though.
In the meantime, this is an interesting approach:
https://github.com/timo/ikiwiki/commit/a73837a8f26147e42a0bb2dde38b4890b27822b3
[[!directive text=<<FOO
...
FOO]]
Since that's implemented, I will probably just merge it,
once I satisfy myself it doesn't blow up in any edge cases.
(It also adds triple single quotes as a third, distinct type of quotes,
which feels a bit redundant given the here docs.) --[[Joey]]
Hmm, that patch changes a m///sgx to a m///msgx. Meaning
that any '^' or '$' inside the regexp will change behavior from matching
the start/end of string to matching the start/end of individual lines
within the string. And there is one legacy '$' which must then
change behavior; the "delimiter to next param".
So, I'm not sure what behavior that will cause, but I suspect it will
be a bug. Unless the `\s+|$' already stops matching at a newline within
the string like it's whitespace. That needs more alalysis.
Also, the patch seems incomplete, only patching the first regexp
but not the other two in the same function, which also are quoting-aware. --[[Joey]]