+> Very belated code review of last version of the patch:
+>
+> * `is_globlist` is no longer needed
+
+>> 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]]
+
+>>>>> You're right -- I did not think the recursive case through.
+>>>>> --[[Joey]]
+
+> * 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]]
+
+>>>>> I think we could get rid of it. `bestlink` will lc it itself
+>>>>> if the uppercase version does not exist; `match_glob` matches
+>>>>> insensitively.
+>>>>> --[[Joey]]
+
+> * 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
+> pagespecs with. It would be possible to move this check
+> to `pagespec_makeperl`, by having it check if the parameter
+> passed to a pagespec function looked like a named pagespec.
+> The only issue is that some pagespec functions take a parameter
+> 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.
+
+>>>> Yes, and it can do that in just three lines of code. But if we automatically check for named pagespecs all the time we
+>>>> potentially break any matching function that doesn't accept pages, or wants to use multiple arguments.
+
+>>>>> 3 lines of code, plus the functions called become part of the API,
+>>>>> don't forget about that..
+>>>>>
+>>>>> Yes, I think that is the tradeoff, the question is whether to export
+>>>>> the additional complexity needed for that flexability.
+>>>>>
+>>>>> I'd be suprised if multiple argument pagespecs become necessary..
+>>>>> with the exception of this patch there has been no need for them yet.
+>>>>>
+>>>>> There are lots of pagespecs that take data other than pages,
+>>>>> indeed, that's really the common case. So far, none of them
+>>>>> seem likely to take data that starts with a `~`. Perhaps
+>>>>> the thing to do would be to check if `~foo` is a known,
+>>>>> named pagespec, and if not, just pass it through unchanged.
+>>>>> Then there's little room for ambiguity, and this also allows
+>>>>> pagespecs like `glob(~foo*)` to match the literal page `~foo`.
+>>>>> (It will make pagespec_merge even harder tho.. see below.)
+>>>>> --[[Joey]]
+
+>>>>>> I've already used multi-argument pagespec match functions in
+>>>>>> my data plugin. It is used for having different types of links. If
+>>>>>> you want to have multiple types of links, then the match function
+>>>>>> for them needs to take both the link name and the link type.
+>>>>>> I'm trying to think of a way we could have both - automatically
+>>>>>> handle the existential case unless the function indicates somehow
+>>>>>> that it'll do it itself. Any ideas? -- [[Will]]
+
+> * 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]]
+
+>>>> I think this can happen in the new closure based code. I don't think this could happen in the old code. -- [[Will]]
+
+>>>> 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]]
+
+>>>> Perhaps the thing to do is to have a `clear_defines()`
+>>>> function, then merging `A` and `B` yields `(A) or (clear_defines() and (B))`
+>>>> That would deal with both the cases where `A` and `B` differently
+>>>> define `~foo` as well as with the case where `A` defines `~foo` while
+>>>> `B` uses it to refer to a literal page.
+>>>> --[[Joey]]
+
+>>>>> I don't think this will work with the new patch, and I don't think it was needed with the old one.
+>>>>> Under the old patch, pagespec_makeperl() generated a string of unevaluated, self-contained, perl
+>>>>> code. When a new named pagespec was defined, a recursive call was made to get the perl code
+>>>>> for the pagespec, and then that code was used to add something like `$params{specFuncs}->{name} = sub {recursive code} and `
+>>>>> to the result of the calling function. This means that at pagespec testing time, when this code is executed, the
+>>>>> specFuncs hash is built up as the pagespec is checked. In the case of the 'or' used above, later redefinitions of
+>>>>> a named pagespec would have redefined the specFunc at the right time. It should have just worked. However...
+
+>>>>> Since my original patch, you started using closures for security reasons (and I can see the case for that). Unfortunately this
+>>>>> means that the generated perl code is no longer self-contained - it needs to be evaluated in the same closure it was generated
+>>>>> so that it has access to the data array. To make this work with the recursive call I had two options: a) make the data array a
+>>>>> reference that I pass around through the pagespec_makeperl() functions and have available when the code is finally evaluated
+>>>>> in pagespec_translate(), or b) make sure that each pagespec is evaluated in its correct closure and a perl function is returned, not a
+>>>>> string containing unevaluated perl code.
+
+>>>>> I went with option b). I did it in such a way that the hash of specfuncs is built up at translation time, not at execution time. This
+>>>>> means that with the new code you can call specfuncs that get defined out of order:
+
+ ~test and define(~test, blah)
+
+>>>>> but it also means that using a simple 'or' to join two pagespecs wont work. If you do something like this:
+
+ ~test and define(~test, foo) and define(~test, baz)
+
+>>>>> then the last definition (baz) takes precedence.
+>>>>> In the process of writing this I think I've come up with a way to change this back the way it was, still using closures. -- [[Will]]
+
+>>> My [[remove-pagespec-merge|should_optimise_pagespecs]] branch has now
+>>> solved all this by deleting the offending function :-) --[[smcv]]
+
+>> 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.
+
+>>>>>> Note that inline and map currently achieve the second type of dependency by
+>>>>>> explicitly calling `add_depends` for each page the displayed.
+>>>>>> If any of those pages are removed, the regular pagespec would not
+>>>>>> match them -- since they're gone. However, the explicit dependency
+>>>>>> on them does cause them to match. It's an ugly corner I'd like to
+>>>>>> get rid of. --[[Joey]]
+
+>>>>> 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.
+
+>>>>>> An example of the current system not tracking enough data is
+>>>>>> where A inlines B which inlines C. A change to C will cause B to
+>>>>>> rebuild, but A will not "notice" that B has implicitly changed.
+>>>>>> That example suggests it might be fixable without explicitly storing
+>>>>>> data, by causing a rebuild of B to be treated as a change to B.
+>>>>>> --[[Joey]]
+
+>>>>> 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]]
+
+Patch updated to use closures rather than inline generated code for named pagespecs. Also includes some new use of ErrorReason where appropriate. -- [[Will]]
+
+> * Perl really doesn't need forward declarations, honest!
+
+>> It complained (warning, not error) when I didn't use the forward declaration. :(
+
+> * I have doubts about memoizing the anonymous sub created by
+> `pagespec_translate`.
+
+>> This is there explicitly to make sure that runtime is polynomial and not exponential.
+
+> * Think where you wrote `+{}` you can just write `{}`
+
+>> Possibly :) -- [[Will]]
+