ikiwiki/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