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/410bbaf141036164f92009599ae12790b1530886
(the link has since been fixed twice)
\[[!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.
Update: seems it does, I'm fairly satisfied that is not a bug.
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]]
Yes, I'm terribly sorry. I actually did edit the other two regexps, but
I apparently missed copying it over as well. Should have been doing this
in a git repo all along. Look at the new commit I put atop it that has
the rest as well:
(redacted: is now part of the commit linked to from above)
Also: I'm not sure any more, why I added the m modifier. It was very
late at night and I was getting a bit desperate (turned out, the next
morning, I put my extra regexes after the "unquoted value" one. heh.)
So, feel free to fix that. --Timo
I've fixed the patch by rebasing, fixed the link above. I'm still not
sure if the m modifier for the regex is still needed (apparently I
didn't put it in the other regexes. Not completely sure about the
implications.) Am now trying to wrap my head around a test case to
test the new formats for a bit. --Timo