>
>> I thought about this briefly, and got about that far.. glad you got
>> further. :-) --[[Joey]]
+
+>> Or, one [[!taglink could_also_refer|pagespec_in_DL_style]] to the language of [[!wikipedia description logics]]: their formulas actually define classes of objects through quantified relations to other classes. --Ivan Z.
>
> Another option would be go with a more functional syntax. The concept here would
> be to allow a pagespec to appear in a 'pagespec function' anywhere a page can. e.g.
>> So, equivilant example: `define(bugs, bugs/* and !*/Discussion) and define(openbugs, bugs and !link(done)) and openbugs and !link(openbugs)`
>>
+
>> Re recursion, it is avoided.. but building a pagespec that is O(N^X) where N is the
>> number of pages in the wiki is not avoided. Probably need to add DOS prevention.
>> --[[Joey]]
>>>> Yeah, guess that'd work. :-)
-> One quick further thought. All the above discussion assumes that 'dependency' is the
+> <a id="another_kind_of_links" />One quick further thought. All the above discussion assumes that 'dependency' is the
> same as 'links to', which is not really true. For example, you'd like to be able to say
> "This bug does not depend upon [ [ link to other bug ] ]" and not have a dependency.
> Without having different types of links, I don't see how this would be possible.
>
> -- [[Will]]
+>> I saw that this issue is targeted at by the work on [[structured page data#another_kind_of_links]]. --Ivan Z.
+
Okie - I've had a quick attempt at this. Initial patch attached. This one doesn't quite work.
And there is still a lot of debugging stuff in there.
> Very belated code review of last version of the patch:
>
> * `is_globlist` is no longer needed
-> * `pagespec_translate` is already memoized, so the explicit call
-> to memoize when handling a define seems unnecessary?
+
+>> Good :)
+
> * I don't understand why the pagespec match regexp is changed
> from having flags `igx` to `ixgs`. Don't see why you
> want `.` to match '\n` in it, and don't see any `.` in the regexp
> anyway?
+
+>> Because you have to define all the named pagespecs in the pagespec, you sometimes end up with very long pagespecs. I found it useful to split them over multiple lines. That didn't work at one point and I added the 's' to make it work. I may have further altered the regex since then to make the 's' redundant. Remove it and see if multi-line pagespecs still work. :)
+
+>>> Well, I can tell you that multi-line pagespecs are supported w/o
+>>> your patch .. I use them all the time. The reason I find your
+>>> use of `/s` unlikely is because without it `\s` already matches
+>>> a newline. Only if you want to treat a newline as non-whitespace
+>>> is `/s` typically necessary. --[[Joey]]
+
> * Some changes of `@_` to `%params` in `pagespec_makeperl` do not
> make sense to me. I don't see where \%params is defined and populated,
> except with `\$params{specFunc}`.
+
+>> I'm not a perl hacker. This was a mighty battle for me to get going.
+>> There is probably some battlefield carnage from my early struggles
+>> learning perl left here. Part of this is that @_ / @params already
+>> existed as a way of passing in extra parameters. I didn't want to
+>> pollute that top level namespace - just at my own parameter (a hash)
+>> which contained the data I needed.
+
+>>> I think I understand how the various `%params`
+>>> (there's not just one) work in your code now, but it's really a mess.
+>>> Explaining it in words would take pages.. It could be fixed by,
+>>> in `pagespec_makeperl` something like:
+>>>
+>>> my %specFuncs;
+>>> push @_, specFuncs => \%specFuncs;
+>>>
+>>> With that you have the hash locally available for populating
+>>> inside `pagespec_makeperl`, and when the `match_*` functions
+>>> are called the same hash data will be available inside their
+>>> `@_` or `%params`. No need to change how the functions are called
+>>> or do any of the other hacks.
+>>>
+>>> Currently, specFuncs is populated by building up code
+>>> that recursively calls `pagespec_makeperl`, and is then
+>>> evaluated when the pagespec gets evaluated. My suggested
+>>> change to `%params` will break that, but that had to change
+>>> anyway.
+>>>
+>>> It probably has a security hole, and is certianly inviting
+>>> one, since the pagespec definition is matched by a loose regexp (`.*`)
+>>> and then subject to string interpolation before being evaluated
+>>> inside perl code. I recently changed ikiwiki to never interpolate
+>>> user-supplied strings when translating pagespecs, and that
+>>> needs to happen here too. The obvious way, it seems to me,
+>>> is to not generate perl code, but just directly run perl code that
+>>> populates specFuncs.
+
+>>>> I don't think this is as bad as you make out, but your addition of the
+>>>> data array will break with the recursion my patch adds in pagespec_makeperl.
+>>>> To fix that I'll need to pass a reference to that array into pagespec_makeperl.
+>>>> I think I can then do the same thing to $params{specFuncs}. -- [[Will]]
+
> * Seems that the only reason `match_glob` has to check for `~` is
> because when a named spec appears in a pagespec, it is translated
> to `match_glob("~foo")`. If, instead, `pagespec_makeperl` checked
> for named specs, it could convert them into `check_named_spec("foo")`
> and avoid that ugliness.
+
+>> Yeah - I wanted to make named specs syntactically different on my first pass. You are right in that this could be made a fallback - named specs always override pagenames.
+
> * The changes to `match_link` seem either unecessary, or incomplete.
> Shouldn't it check for named specs and call
> `check_named_spec_existential`?
+
+>> An earlier version did. Then I realised it wasn't actually needed in that case - match_link() already included a loop that was like a type of existential matching. Each time through the loop it would
+>> call match_glob(). match_glob() in turn will handle the named spec. I tested this version briefly and it seemed to work. I remember looking at this again later and wondering if I had mis-understood
+>> some of the logic in match_link(), which might mean there are cases where you would need an explicit call to check_named_spec_existential() - I never checked it properly after having that thought.
+
+>>> In the common case, `match_link` does not call `match_glob`,
+>>> because the link target it is being asked to check for is a single
+>>> page name, not a glob.
+
+>>>> A named pagespec should fall into the glob case. These two pagespecs should be the same:
+
+ link(a*)
+
+>>>> and
+
+ define(aStar, a*) and link(aStar)
+
+>>>> In the first case, we want the pagespec to match any page that links to a page matching the glob.
+>>>> In the second case, we want the pagespec to match any page that links to a page matching the named spec.
+>>>> match_link() was already doing existential part. The patches to this code were simply to remove the `lc()`
+>>>> call from the named pagespec name. Can that `lc` be removed entirely? -- [[Will]]
+
> * Generally, the need to modify `match_*` functions so that they
> check for and handle named pagespecs seems suboptimal, if
> only because there might be others people may want to use named
> that is not a page name at all, and it could be weird
> if such a parameter were accidentially interpreted as a named
> pagespec. (But, that seems unlikely to happen.)
+
+>> Possibly. I'm not sure which I prefer between the current solution and that one. Each have advantages and disadvantages.
+>> It really isn't much code for the match functions to add a call to check_named_spec_existential().
+
+>>> But if a plugin adds its own match function, it has
+>>> to explicitly call that code to support named pagespecs.
+
> * I need to check if your trick to avoid infinite recursion
> works if there are two named specs that recursively
> call one-another. I suspect it does, but will test this
> myself..
->
+
+>> It worked for me. :)
+
+> * I also need to verify if memoizing the named pagespecs has
+> really guarded against very expensive pagespecs DOSing the wiki..
+
> --[[Joey]]
+>> There is one issue that I've been thinking about that I haven't raised anywhere (or checked myself), and that is how this all interacts with page dependencies.
+>> Firstly, I'm not sure anymore that the `pagespec_merge` function will continue to work in all cases.
+
+>>> The problem I can see there is that if two pagespecs
+>>> get merged and both use `~foo` but define it differently,
+>>> then the second definition might be used at a point when
+>>> it shouldn't (but I haven't verified that really happens).
+>>> That could certianly be a show-stopper. --[[Joey]]
+
+>>>> Even if that works, this is a good argument for having a syntactic difference between named pagespecs and normal pages.
+>>>> If you're joining two pagespecs with 'or', you don't want a named pagespec in the first part overriding a page name in the
+>>>> second part. Oh, and I assume 'or' has the right operator precedence that "a and b or c" is "(a and b) or c", and not "a and (b or c)" -- [[Will]]
+
+>>>>> Looks like its bracketed in the code anyway... -- [[Will]]
+
+>> Secondly, it seems that there are two types of dependency, and ikiwiki
+>> currently only handles one of them. The first type is "Rebuild this
+>> page when any of these other pages changes" - ikiwiki handles this.
+>> The second type is "rebuild this page when set of pages referred to by
+>> this pagespec changes" - ikiwiki doesn't seem to handle this. I
+>> suspect that named pagespecs would make that second type of dependency
+>> more important. I'll try to come up with a good example. -- [[Will]]
+
+>>> Hrm, I was going to build an example of this with backlinks, but it
+>>> looks like that is handled as a special case at the moment (line 458 of
+>>> render.pm). I'll see if I can breapk
+>>> things another way. Fixing this properly would allow removal of that special case. -- [[Will]]
+
+>>>> I can't quite understand the distinction you're trying to draw
+>>>> between the two types of dependencies. Backlinks are a very special
+>>>> case though and I'll be suprised if they fit well into pagespecs.
+>>>> --[[Joey]]
+
+>>>>> The issue is that the existential pagespec matching allows you to build things that have similar
+>>>>> problems to backlinks.
+>>>>> e.g. the following inline:
+
+ \[[!inline pages="define(~done, link(done)) and link(~done)" archive=yes]]
+
+>>>>> includes any page that links to a page that links to done. Now imagine I add a new link to 'done' on
+>>>>> some random page somewhere - a page which some other page links to which didn't previously get included - the set of pages accepted by the pagespec, and hence the set of
+>>>>> pages inlined, will change. But, there is no dependency anywhere on the page that I altered, so
+>>>>> ikiwiki will not rebuild the page with the inline in it. What is happening is that the page that I altered affects
+>>>>> the set of pages matched by the pagespec without itself being matched by the pagespec, and hence included in the dependency list.
+
+>>>>> To make this work well, I think you need to recognise two types of dependencies for each page (and no
+>>>>> special cases for particular types of links, eg backlinks). The first type of dependency says, "The content of
+>>>>> this page depends upon the content of these other pages". The `add_depends()` in the shortcuts
+>>>>> plugin is of this form: any time the shortcuts page is edited, any page with a shortcut on it
+>>>>> is rebuilt. The inline plugin also needs to add dependencies of this form to detect when the inlined
+>>>>> content changes. By contrast, the map plugin does not need a dependency of this form, because it
+>>>>> doesn't actually care about the content of any pages, just which pages it needs to include (which we'll handle next).
+
+>>>>> The second type of dependency says, "The content of this page depends upon the exact set of pages matched
+>>>>> by this pagespec". The first type of dependency was about the content of some pages, the second type is about
+>>>>> which pages get matched by a pagespec. This is the type of dependency tracking that the map plugin needs.
+>>>>> If the set of pages matched by map pagespec changes, then the page with the map on it needs to be rebuilt to show a different list of pages.
+>>>>> Inline needs this type of dependency as well as the previous type - This type handles a change in which pages
+>>>>> are inlined, the previous type handles a change in the content of any of those pages. Shortcut does not need this type of
+>>>>> dependency. Most of the places that use `add_depends()` seem to need this type of dependency rather than the first type.
+
+>>>>> Implementation Details: The first type of dependency can be handled very similarly to the current
+>>>>> dependency system. You just need to keep a list of pages that the content depends upon. You could
+>>>>> keep that list as a pagespec, but if you do this you might want to check that the pagespec doesn't change,
+>>>>> possibly by adding a dependency of the second type along with the dependency of the first type.
+
+>>>>> The second type of dependency is a little more tricky. For each page, we'd need a list of pagespecs that
+>>>>> the page depended on, and for each pagespec you'd want to store the list of pages that currently match it.
+>>>>> On refresh, you'd need to check each pagespec to see if the set of pages that match it has changed, and if
+>>>>> that set has changed, then rebuild the dependent page(s). Oh, and for this second type of dependency, I
+>>>>> don't think you can merge pagespecs. If I wanted to know if either "\*" or "link(done)" changes, then just checking
+>>>>> to see if the set of pages matched by "\* or link(done)" changes doesn't work.
+
+>>>>> The current system works because even though you usually want dependencies of the second type, the set of pages
+>>>>> referred to by a pagespec can only change if one of those pages itself changes. i.e. A dependency check of the
+>>>>> first type will catch a dependency change of the second type with current pagespecs.
+>>>>> This doesn't work with backlinks, and it doesn't work with existential matching. Backlinks are currently special-cased. I don't know
+>>>>> how to special-case existential matching - I suspect you're better off just getting the dependency tracking right.
+
+>>>>> I also tried to come up with other possible solutions: e.g. can we find the dependencies for a pagespec? That
+>>>>> would be the set of pages where a change on one of those pages could lead to a change in the set of pages matched by the pagespec.
+>>>>> For old-style pagespecs without backlinks, the dependency set for a pagespec is the same as the set of pages the pagespec matches.
+>>>>> Unfortunately, with existential matching, the set of pages that each
+>>>>> pagespec depends upon can quickly become "*", which is not very useful. -- [[Will]]
+
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