I like the idea of [[tips/integrated_issue_tracking_with_ikiwiki]], and I do so on several wikis.  However, as far as I can tell, ikiwiki has no functionality which can represent dependencies between bugs and allow pagespecs to select based on dependencies.  For instance, I can't write a pagespec which selects all bugs with no dependencies on bugs not marked as done.  --[[JoshTriplett]]

> I started having a think about this.  I'm going to start with the idea that expanding
> the pagespec syntax is the way to attack this.  It seems that any pagespec that is going
> to represent "all bugs with no dependencies on bugs not marked as done" is going to
> need some way to represent "bugs not marked as done" as a collection of pages, and
> then represent "bugs which do not link to pages in the previous collection".
>
> One way to do this would be to introduce variables into the pagespec, along with
> universal and/or existential [[!wikipedia Quantification]].  That looks quite complex.
>
>> I thought about this briefly, and got about that far.. glad you got
>> further. :-) --[[Joey]]
> 
> 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.
> I could pass a pagespec to `link()` and that would return true if there is a link to any
> page matching the pagespec.  This makes the variables and existential quantification
> implicit.  It would allow the example requested above:
>
>> `bugs/* and !*/Discussion and !link(bugs/* and !*/Discussion and !link(done))`
>
> Unfortunately, this is also going to make the pagespec parsing more complex because
> we now need to parse nested sets of parentheses to know when the nested pagespec
> ends, and that isn't a regular language (we can't use regular expression matching for
> easy parsing).
>
>> Also, it may cause ambiguities with page names that contain parens
>> (though some such ambigutities already exist with the pagespec syntax).
>
> One simplification of that would be to introduce some pagespec [[shortcuts]].  We could
> then allow pagespec functions to take either pages, or named pagespec shortcuts.  The
> pagespec shortcuts would just be listed on a special page, like current [[shortcuts]].
> (It would probably be a good idea to require that shortcuts on that page can only refer
> to named pagespecs higher up that page than themselves.  That would stop some
> looping issues...)  These shortcuts would be used as follows: when trying to match
> a page (without globs) you look to see if the page exists.  If it does then you have a
> match.  If it doesn't, then you look to see if a similarly named pagespec shortcut
> exists.  If it does, then you check that pagespec recursively to see if you have a match.
> The ordering requirement on named pagespecs stops infinite recursion.
>
> Does that seem like a reasonable first approach?
>
> -- [[Will]]

>> Having a separate page for the shortcuts feels unwieldly.. perhaps
>> instead the shortcut could be defined earlier in the scope of the same
>> pagespec that uses it?
>> 
>> Example: `define(~bugs, bugs/* and !*/Discussion) and define(~openbugs, ~bugs and !link(done)) and ~openbugs and !link(~openbugs)`

>>> That could work.  parens are only ever nested 1 deep in that grammar so it is regular and the current parsing would be ok.

>> Note that I made the "~" explicit, not implicit, so it could be left out. In the case of ambiguity between
>> a definition and a page name, the definition would win.

>>> That was my initial thought too :), but when implementing it I decided that requiring the ~ made things easier.  I'll probably require the ~ for the first pass at least.

>> 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]]

>>> If you memoize the outcomes of the named pagespecs you can make in O(N.X), no?
>>> -- [[Will]]

>>>> Yeah, guess that'd work. :-)

> 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]]

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.

At the moment I've added a new preprocessor plugin, `definepagespec`, which is like
shortcut for pagespecs.  To reference a named pagespec, use `~` like this:

    [ [!definepagespec name="bugs" spec="bugs/* and !*/Discussion"]]
    [ [!definepagespec name="openbugs" spec="~bugs and !link(done)"]]
    [ [!definepagespec name="readybugs" spec="~openbugs and !link(~openbugs)"]]

At the moment the problem is in `match_link()` when we're trying to find a sub-page that
matches the appropriate page spec.  There is no good list of pages available to iterate over.

    foreach my $nextpage (keys %IkiWiki::pagesources)

does not give me a good list of pages.  I found the same thing when I was working on
this todo [[todo/Add_a_plugin_to_list_available_pre-processor_commands]].

> I'm not sure why iterating over `%pagesources` wouldn't work here, it's the same method
> used by anything that needs to match a pagespec against all pages..? --[[Joey]]

>> My uchecked hypothesis is that %pagesources is created after the refresh hook.
>> I've also been concerned about how globally defined pagespec shortcuts would interact with
>> the page dependancy system.  Your idea of internally defined shortcuts should fix that. -- [[Will]]

>>> You're correct, the refresh hook is run very early, before pagesources
>>> is populated. (It will be partially populated on a refresh, but will
>>> not be updated to reflect new pages.) Agree that internally defined
>>> seems the way to go. --[[Joey]]

Immediately below is a patch which seems to basically work.  Lots of debugging code is still there
and it needs a cleanup, but I thought it worth posting at this point.  (I was having problems
with old style glob lists, so i just switched them off for the moment.)

The following three inlines work for me with this patch:

    Bugs:
    
    [ [!inline pages="define(~bugs, bugs/* and ! */Discussion) and ~bugs" archive="yes"]]
    
    OpenBugs:
    
    [ [!inline pages="define(~bugs, bugs/* and ! */Discussion) and define(~openbugs,~bugs and !link(done)) and ~openbugs" archive="yes"]]
    
    ReadyBugs:
    
    [ [!inline pages="define(~bugs, bugs/* and ! */Discussion) and define(~openbugs,~bugs and !link(done)) and define(~readybugs,~openbugs and !link(~openbugs)) and ~readybugs" archive="yes"]]

> Nice! Could the specfuncsref be passed in %params? I'd like to avoid
> needing to change the prototype of every pagespec function, since several
> plugins define them too. --[[Joey]]

>> Maybe - it needs more thought.  I also considered it when I was going though changing all those plugins :).
>> My concern was that `%params` can contain other user-defined parameters,
>> e.g. `link(target, otherparameter)`, and that means that the specFuncs could be clobbered by a user (or other
>> weird security hole).  I thought it better to separate it, but I didn't think about it too hard.  I might move it to
>> the first parameter rather than the second.  Ikiwiki is my first real perl hacking and I'm still discovering
>> good ways to write things in perl.
>>
>>>> `%params` contains the parameters passed to `pagespec_match`, not
>>>> user-supplied parameters. The user-supplied parameter to a function
>>>> like `match_glob()` or `match_link()` is passed in the second positional parameter. --[[Joey]]

>>>>> OK.  That seems reasonable then.  The only problem is that my PERLfu is not strong enough to make it
>>>>> work.  I really have to wonder what substance was influencing the designers of PERL...
>>>>> I can't figure out how to use the %params.  And I'm pissed off enough with PERL that I'm not going
>>>>> to try and figure it out any more.  There are two patches below now.  The first one uses an extra
>>>>> argument and works.  The second one tries to use %params and doesn't - take your pick :-). -- [[Will]]

>> What do you think is best to do about `is_globlist()`?  At the moment it requires that the 'second word', as
>> delimited by a space and ignoring parens, is 'and' or 'or'.  This doesn't hold in the above example pagespecs (so I just hard wired it to 0 to test my patch).
>> My thought was just to search for 'and' or 'or' as words anywhere in the pagespec.  Thoughts?

>>> Dunno, we could just finish deprecating it. Or change the regexp to
>>> skip over spaces in parens. (`/[^\s]+\s+([^)]+)/`) --[[Joey]]

>>>> I think I have a working regexp now.

>> Oh, one more thing.  In pagespec_translate (now pagespec_makeperl), there is a part of the regular expression for `# any other text`.
>> This contained `()`, which has no effect.  I replaced that with `\(\)`, but that is a change in the definition of pagespecs unrelated to the
>> rest of this patch. In a related change, commands were not able to contain `)` in their parameters.  I've extended that so the cannot
>> contain `(` or `)`.  -- [[Will]]

>>> `[^\s()]+` is a character class matching all characters not spaces or
>>> parens. Since the pervious terminals in the regexp consume most
>>> occurances of an open paren or close paren, it's unlikely for one to
>>> get through to that part of the regexp. For example, "foo()" will be
>>> matched by the command matcher; "(foo)" will be matched by the open
>>> paren literal terminal. "foo(" and "foo)" can get through to the
>>> end, and would be matched as a page name, if it didn't exclude parens.
>>>
>>> So why exclude them? Well, consider "foo and(bar and baz)". We don't
>>> want it to match "and(" as a page name!
>>> 
>>> Escaping the parens in the character class actually changes nothing; the
>>> changed character class still matches all characters not spaces or
>>> parens. (Try it!).
>>> 
>>> Re commands containing '(', I don't really see any reason not to
>>> allow that, unless it breaks something. --[[Joey]]

>>>> Oh, I didn't realise you didn't need to escape parens inside [].  All else I
>>>> I understood.  I have stopped commands from containing parens because
>>>> once you allow that then you might have a extra level of depth in the parsing
>>>> of define() statements. -- [[Will]]

>>> Updated patch.  Moved the specFuncsRef to the front of the arg list.  Still haven't thought through the security implications of
>>> having it in `%params`.  I've also removed all the debugging `print` statements.  And I've updated the `is_globlist()` function.
>>> I think this is ready for people other than me to have a play.  It is not well enough tested to commit just yet.
>>> -- [[Will]]

I've lost track of the indent level, so I'm going back to not indented - I think this is a working [[patch]] taking into
account all comments above (which doesn't mean it is above reproach :) ).  --[[Will]]

----

    diff --git a/IkiWiki.pm b/IkiWiki.pm
    index 4e4da11..8b3cdfe 100644
    --- a/IkiWiki.pm
    +++ b/IkiWiki.pm
    @@ -1550,7 +1550,16 @@ sub globlist_to_pagespec ($) {
     
     sub is_globlist ($) {
     	my $s=shift;
    -	return ( $s =~ /[^\s]+\s+([^\s]+)/ && $1 ne "and" && $1 ne "or" );
    +	return ! ($s =~ /
    +			(^\s*
    +				[^\s(]+		# single item
    +					(\(			# possibly with parens after it
    +						([^)]*	# with stuff inside those parens
    +						(\([^)]*\))*)*	# maybe even nested parens
    +					\))?\s*$
    +			) |
    +				(\s and \s) | (\s or \s)	# or we find 'and' or 'or' somewhere
    +			/xs);
     }
     
     sub safequote ($) {
    @@ -1631,7 +1640,7 @@ sub pagespec_merge ($$) {
     	return "($a) or ($b)";
     }
     
    -sub pagespec_translate ($) {
    +sub pagespec_makeperl ($) {
     	my $spec=shift;
     
     	# Support for old-style GlobLists.
    @@ -1650,12 +1659,14 @@ sub pagespec_translate ($) {
     		|
     			\)		# )
     		|
    -			\w+\([^\)]*\)	# command(params)
    +			define\(\s*~\w+\s*,((\([^()]*\)) | ([^()]+))+\)	# define(~specName, spec) - spec can contain parens 1 deep
    +		|
    +			\w+\([^()]*\)	# command(params) - params cannot contain parens
     		|
     			[^\s()]+	# any other text
     		)
     		\s*		# ignore whitespace
    -	}igx) {
    +	}igxs) {
     		my $word=$1;
     		if (lc $word eq 'and') {
     			$code.=' &&';
    @@ -1666,16 +1677,23 @@ sub pagespec_translate ($) {
     		elsif ($word eq "(" || $word eq ")" || $word eq "!") {
     			$code.=' '.$word;
     		}
    -		elsif ($word =~ /^(\w+)\((.*)\)$/) {
    +		elsif ($word =~ /^define\(\s*~(\w+)\s*,(.*)\)$/s) {
    +			$code .= " (\$params{specFuncs}->{$1}=";	# (exists \$params{specFuncs}) && 
    +			$code .= "memoize(";
    +			$code .= &pagespec_makeperl($2);
    +			$code .= ")";
    +			$code .= ") ";
    +		}
    +		elsif ($word =~ /^(\w+)\((.*)\)$/s) {
     			if (exists $IkiWiki::PageSpec::{"match_$1"}) {
    -				$code.="IkiWiki::PageSpec::match_$1(\$page, ".safequote($2).", \@_)";
    +				$code.="IkiWiki::PageSpec::match_$1(\$page, ".safequote($2).", \%params)";
     			}
     			else {
     				$code.=' 0';
     			}
     		}
     		else {
    -			$code.=" IkiWiki::PageSpec::match_glob(\$page, ".safequote($word).", \@_)";
    +			$code.=" IkiWiki::PageSpec::match_glob(\$page, ".safequote($word).", \%params)";
     		}
     	}
     
    @@ -1683,8 +1701,18 @@ sub pagespec_translate ($) {
     		$code=0;
     	}
     
    +	return 'sub { my $page=shift; my %params = @_; '.$code.' }';
    +}
    +
    +sub pagespec_translate ($) {
    +	my $spec=shift;
    +
    +	my $code = pagespec_makeperl($spec);
    +
    +	# print STDERR "Spec '$spec' generated code '$code'\n";
    +
     	no warnings;
    -	return eval 'sub { my $page=shift; '.$code.' }';
    +	return eval $code;
     }
     
     sub pagespec_match ($$;@) {
    @@ -1699,7 +1727,7 @@ sub pagespec_match ($$;@) {
     
     	my $sub=pagespec_translate($spec);
     	return IkiWiki::FailReason->new("syntax error in pagespec \"$spec\"") if $@;
    -	return $sub->($page, @params);
    +	return $sub->($page, @params, specFuncs => {});
     }
     
     sub pagespec_valid ($) {
    @@ -1748,11 +1776,78 @@ sub new {
     
     package IkiWiki::PageSpec;
     
    +sub check_named_spec($$;@) {
    +	my $page=shift;
    +	my $specName=shift;
    +	my %params=@_;
    +	
    +	error("Unable to find specFuncs in params to check_named_spec()!") unless exists $params{specFuncs};
    +
    +	my $specFuncsRef=$params{specFuncs};
    +	
    +	return IkiWiki::FailReason->new("Named page spec '$specName' is not valid")
    +		unless (substr($specName, 0, 1) eq '~');
    +	
    +	$specName = substr($specName, 1);
    +
    +	if (exists $specFuncsRef->{$specName}) {
    +		# remove the named spec from the spec refs
    +		# when we recurse to avoid infinite recursion
    +		my $sub = $specFuncsRef->{$specName};
    +		delete $specFuncsRef->{$specName};
    +		my $result = $sub->($page, %params);
    +		$specFuncsRef->{$specName} = $sub;
    +		return $result;
    +	} else {
    +		return IkiWiki::FailReason->new("Page spec '$specName' does not exist");
    +	}
    +}
    +
    +sub check_named_spec_existential($$$;@) {
    +	my $page=shift;
    +	my $specName=shift;
    +	my $funcref=shift;
    +	my %params=@_;
    +	
    +	error("Unable to find specFuncs in params to check_named_spec_existential()!") unless exists $params{specFuncs};
    +	my $specFuncsRef=$params{specFuncs};
    +	
    +	return IkiWiki::FailReason->new("Named page spec '$specName' is not valid")
    +		unless (substr($specName, 0, 1) eq '~');
    +	$specName = substr($specName, 1);
    +	
    +	if (exists $specFuncsRef->{$specName}) {
    +		# remove the named spec from the spec refs
    +		# when we recurse to avoid infinite recursion
    +		my $sub = $specFuncsRef->{$specName};
    +		delete $specFuncsRef->{$specName};
    +		
    +		foreach my $nextpage (keys %IkiWiki::pagesources) {
    +			if ($sub->($nextpage, %params)) {
    +				my $tempResult = $funcref->($page, $nextpage, %params);
    +				if ($tempResult) {
    +					$specFuncsRef->{$specName} = $sub;
    +					return $tempResult;
    +				}
    +			}
    +		}
    +		
    +		$specFuncsRef->{$specName} = $sub;
    +		return IkiWiki::FailReason->new("No page in spec '$specName' was successfully matched");
    +	} else {
    +		return IkiWiki::FailReason->new("Named page spec '$specName' does not exist");
    +	}
    +}
    +
     sub match_glob ($$;@) {
     	my $page=shift;
     	my $glob=shift;
     	my %params=@_;
     	
    +	if (substr($glob, 0, 1) eq '~') {
    +		return check_named_spec($page, $glob, %params);
    +	}
    +
     	my $from=exists $params{location} ? $params{location} : '';
     	
     	# relative matching
    @@ -1782,11 +1877,12 @@ sub match_internal ($$;@) {
     
     sub match_link ($$;@) {
     	my $page=shift;
    -	my $link=lc(shift);
    +	my $fulllink=shift;
     	my %params=@_;
    +	my $link=lc($fulllink);
     
     	my $from=exists $params{location} ? $params{location} : '';
    -
    +	
     	# relative matching
     	if ($link =~ m!^\.! && defined $from) {
     		$from=~s#/?[^/]+$##;
    @@ -1804,19 +1900,32 @@ sub match_link ($$;@) {
     		}
     		else {
     			return IkiWiki::SuccessReason->new("$page links to page $p matching $link")
    -				if match_glob($p, $link, %params);
    +				if match_glob($p, $fulllink, %params);
     		}
     	}
     	return IkiWiki::FailReason->new("$page does not link to $link");
     }
     
     sub match_backlink ($$;@) {
    -	return match_link($_[1], $_[0], @_);
    +	my $page=shift;
    +	my $backlink=shift;
    +	my @params=@_;
    +
    +	if (substr($backlink, 0, 1) eq '~') {
    +		return check_named_spec_existential($page, $backlink, \&match_backlink, @params);
    +	}
    +
    +	return match_link($backlink, $page, @params);
     }
     
     sub match_created_before ($$;@) {
     	my $page=shift;
     	my $testpage=shift;
    +	my @params=@_;
    +
    +	if (substr($testpage, 0, 1) eq '~') {
    +		return check_named_spec_existential($page, $testpage, \&match_created_before, @params);
    +	}
     
     	if (exists $IkiWiki::pagectime{$testpage}) {
     		if ($IkiWiki::pagectime{$page} < $IkiWiki::pagectime{$testpage}) {
    @@ -1834,6 +1943,11 @@ sub match_created_before ($$;@) {
     sub match_created_after ($$;@) {
     	my $page=shift;
     	my $testpage=shift;
    +	my @params=@_;
    +
    +	if (substr($testpage, 0, 1) eq '~') {
    +		return check_named_spec_existential($page, $testpage, \&match_created_after, @params);
    +	}
     
     	if (exists $IkiWiki::pagectime{$testpage}) {
     		if ($IkiWiki::pagectime{$page} > $IkiWiki::pagectime{$testpage}) {