ikiwiki/doc/todo/tracking_bugs_with_dependencies.mdwn

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.
>
> 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).
>
> 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]]

> 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]]