X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/0ebb44955aaf454974b9e92f23539bd0e83aee59..bc4ef28f3ebc396096b7eccad04eea6febac8d38:/doc/todo/dependency_types.mdwn diff --git a/doc/todo/dependency_types.mdwn b/doc/todo/dependency_types.mdwn index 74d58a9e5..479cc95cc 100644 --- a/doc/todo/dependency_types.mdwn +++ b/doc/todo/dependency_types.mdwn @@ -188,7 +188,8 @@ before and it is present now. Should this cause a re-build of any page that has > Yes, a presence dep will trigger when a page is added, or removed. > Your example is valid.. but it's also not handled right by normal, -> (content) dependencies, for the same reasons. --[[Joey]] +> (content) dependencies, for the same reasons. Still, I think I've +> addressed it with the pagespec influence stuff below. --[[Joey]] I think that is another version of the problem you encountered with meta-data. @@ -229,16 +230,7 @@ sigh. > I have also been thinking about some sort of analysis pass over pagespecs > to determine what metadata, pages, etc they depend on. It is indeed -> tricky to do. Even if it's just limited to returning a list of pages -> as you suggest. -> -> Consider: For a `*` glob, it has to return a list of all pages -> in the wiki. Which is expensive. And what if the pagespec is -> something like `* and backlink(index)`? Without analyising the -> boolean relationship between terms, the returned list -> will have many more items in it than it should. Or do we not make -> globs return their matches? (If so we have to deal with those -> with one of the other methods disucssed.) --[[Joey]] +> tricky to do. More thoughts on influence lists a bit below. --[[Joey]] ---- @@ -289,13 +281,144 @@ changed pages. ---- -What if there were a function that added a dependency, and at the same time -returned a list of pages matching the pagespec? Plugins that use this would -be exactly the ones, like inline and map, for which this is a problem, and -which already do a match pass over all pages. +Found a further complication in presence dependencies. Map now uses +presence dependencies when adding its explicit dependencies on pages. But +this defeats the purpose of the explicit dependencies! Because, now, +when B is changed to not match a pagespec, the A's presence dep does +not fire. -Adding explicit dependencies during this pass would thus be nearly free. -Not 100% free since it would add explicit deps for things that are not -shown on an inline that limits its display to the first sorted N items. -I suppose we could reach 100% free by making the function also handle -sorting and limiting, though that could be overkill. +I didn't think things through when switching it to use presence +dependencies there. But, if I change it to use full dependencies, then all +the work that was done to allow map to use presence dependencies for its +main pagespec is for naught. The map will once again have to update +whenever *any* content of the page changes. + +This points toward the conclusion that explicit dependencies, however they +are added, are not the right solution at all. Some other approach, such as +maintaining the list of pages that match a dependency, and noticing when it +changes, is needed. + +---- + +### pagespec influence lists + +I'm using this term for the concept of a list of pages whose modification +can indirectly influence what pages a pagespec matches. + +#### Examples + +* The pagespec "created_before(foo)" has an influence list that contains foo. + The removal or (re)creation of foo changes what pages match it. + +* The pagespec "foo" has an empty influence list. This is because a + modification/creation/removal of foo directly changes what the pagespec + matches. + +* The pagespec "*" has an empty influence list, for the same reason. + Avoiding including every page in the wiki into its influence list is + very important! + +* The pagespec "title(foo)" has an influence list that contains every page + that currently matches it. A change to any matching page can change its + title. Why is that considered an indirect influence? Well, the pagespec + might be used in a presence dependency, and so its title changing + would not directly affect the dependency. + +* The pagespec "backlink(index)" has an influence list + that contains index (because a change to index changes the backlinks). + +* The pagespec "link(done)" has an influence list that + contains every page that it matches. A change to any matching page can + remove a link and make it not match any more, and so the list is needed + due to the removal problem. + +#### Low-level Calculation + +One way to calculate a pagespec's influence would be to +expand the SuccessReason and FailReason objects used and returned +by `pagespec_match`. Make the objects be created with an +influence list included, and when the objects are ANDed or ORed +together, combine the influence lists. + +That would have the benefit of allowing just using the existing `match_*` +functions, with minor changes to a few of them to gather influence info. + +But does it work? Let's try some examples: + +Consider "bugs/* and link(done) and backlink(index)". + +Its influence list contains index, and it contains all pages that the whole +pagespec matches. It should, ideally, not contain all pages that link +to done. There are a lot of such pages, and only a subset influence this +pagespec. + +When matching this pagespec against a page, the `link` will put the page +on the list. The `backlink` will put index on the list, and they will be +anded together and combined. If we combine the influences from each +successful match, we get the right result. + +Now consider "bugs/* and link(done) and !backlink(index)". + +It influence list is the same as the previous one, even though a term has +been negated. Because a change to index still influences it, though in a +different way. + +If negation of a SuccessReason preserves the influence list, the right +influence list will be calculated. + +Consider "bugs/* and (link(done) or backlink(index))" +and "bugs/* and (backlink(index) or link(done))' + +Its clear that the influence lists for these are identical. And they +contain index, plus all matching pages. + +When matching the first against page P, the `link` will put P on the list. +The OR needs to be a non-short-circuiting type. (In perl, `or`, not `||` -- +so, `pagespec_translate` will need to be changed to not use `||`.) +Given that, the `backlink` will always be evalulated, and will put index +onto the influence list. If we combine the influences from each +successful match, we get the right result. + +> This is implemented, seems to work ok. --[[Joey]] + +#### High-level Calculation and Storage + +Calculating the full influence list for a pagespec requires trying to match +it against every page in the wiki. + +I'd like to avoid doing such expensive matching redundantly. So add a +`pagespec_match_all`, which returns a list of all pages in the whole +wiki that match the pagespec, and also adds the pagespec as a dependency, +and while it's at it, calculates and stores the influence list. + +It could have an optional sort parameter, and limit parameter, to control +how many items to return and the sort order. So when inline wants to +display the 10 newest, only the influence lists for those ten are added. + +If `pagespec_match_depends` can be used by all plugins, then great, +influences are automatically calculated, no extra work needs to be done. + +If not, and some plugins still need to use `pagespec_match_list` or +`pagespec_match`, and `add_depends`, then I guess that `add_depends` can do +a slightly more expensive influence calculation. + +Bonus: If `add_depends` is doing an influence calculation, then I can remove +the nasty hack it currently uses to decide if a given pagespec is safe to use +with an existence or links dependency. + +Where to store the influence list? Well, it appears that we can just add +(content) dependencies for each item on the list, to the page's +regular list of simple dependencies. So, the data stored ends up looking +just like what is stored today by the explicit dependency hacks. Except, +it's calculated more smartly, and is added automatically. + +> I've implemented influence calculation in `add_depends`. As expected, +> it means rather a lot more work, and makes some things much slower. +> Optimisation via `pagespec_match_depends` next.. --[[Joey]] + +#### Influence types + +Note that influences can also have types, same as dependency types. +For example, "backlink(foo)" has an influence of foo, of type links. +"created_before(foo)" also is influenced by foo, but it's a presence +type. Etc.