X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/6f1ebdd6922a2c96fd57c71cd2052992d13f9c22..bc4ef28f3ebc396096b7eccad04eea6febac8d38:/doc/todo/dependency_types.mdwn diff --git a/doc/todo/dependency_types.mdwn b/doc/todo/dependency_types.mdwn index 58b5ee955..479cc95cc 100644 --- a/doc/todo/dependency_types.mdwn +++ b/doc/todo/dependency_types.mdwn @@ -105,11 +105,11 @@ unnecessary page rebuilds: I propose the following. --[[Joey]] -* Add a second type of dependency, call it an "contentless dependency". +* Add a second type of dependency, call it an "presence dependency". * `add_depends` defaults to adding a regular ("full") dependency, as before. (So nothing breaks.) -* `add_depends($page, $spec, content => 0)` adds an contentless dependency. -* `refresh` only looks at added/removed pages when resolving contentless +* `add_depends($page, $spec, presence => 0)` adds an presence dependency. +* `refresh` only looks at added/removed pages when resolving presence dependencies. This seems straightforwardly doable. I'd like [[Will]]'s feedback on it, if @@ -129,28 +129,296 @@ I implemented the above in a branch. Then I found some problems: * Something simple like pagecount, that seems like it could use a - contentless dependency, can have a pagespec that uses metadata, like + presence dependency, can have a pagespec that uses metadata, like `author()` or `copyright()`. -* pagestats, orphans and brokenlinks cannot use contentless dependencies +* pagestats, orphans and brokenlinks cannot use presence dependencies because they need to update when links change. -Now I'm thinking about having a contentless dependency look at page +Now I'm thinking about having a special dependency look at page metadata, and fire if the metadata changes. And it seems links should either be included in that, or there should be a way to make a dependency that fires when a page's links change. (And what about backlinks?) It's easy to see when a page's links change, since there is `%oldlinks`. To see when metadata is changed is harder, since it's stored in the -pagestate by the meta plugin. +pagestate by the meta plugin. Also, there are many different types of +metadata, that would need to be matched with the pagespecs somehow. Quick alternative: Make add_depends look at the pagespec. Ie, if it -is a simple page name, or a glob, we know a contentless dependency +is a simple page name, or a glob, we know a presence dependency can be valid. If's more complex, convert the dependency from -contentless to full. +presence to full. -There is a lot to dislike about this method. Its parsing of the -pagespec, as currently implemented, does not let plugins add new types of -pagespecs that are contentless. Its pagespec parsing is also subject to +There is a lot to dislike about this method. Its parsing of the pagespec, +as currently implemented, does not let plugins add new types of pagespecs +that only care about presence. Its pagespec parsing is also subject to false negatives (though these should be somewhat rare, and no false positives). Still, it does work, and it makes things like simple maps and pagecounts much more efficient. + +---- + +#### Will's first pass feedback. + +If the API is going to be updated, then it would be good to make it forward compatible. +I'd like for the API to be extendible to what is useful for complex pagespecs, even if we +that is a little redundant at the moment. + +My attempt to play with this is in my git repo. [[!template id=gitbranch branch=origin/depends-spec author="[[will]]"]] +That branch is a little out of date, but if you just look at the changes in IkiWiki.pm you'll see the concept I was looking at. +I added an "add_depends_spec()" function that adds a dependency on the pagespec passed to it. If the set of matched pages +changes, then the dependent page is rebuilt. At the moment the implementation uses the same hack used by map and inline - +just add all the pages that currently exist as traditional content dependencies. + +> As I note below, a problem with this approach is that it has to try +> matching the pagespec against every page, redundantly with the work done +> by the plugin. (But there are ways to avoid that redundant matching.) +> --[[Joey]] + +Getting back to commenting on your proposal: + +Just talking about the definition of a "presence dependency" for the moment, and ignoring implementation. Is a +"presence dependency" supposed to cause an update when a page disappears? I assume so. Is a presence dependency +supposed to cause an update when a pages existence hasn't changed, but it no longer matches the pagespec. +(e.g. you use `created_before(test_page)` in a pagespec, and there was a page, `new_page`, that was created +after `test_page`. `new_page` will not match the spec. Now we'll delete and then re-create `test_page`. Now +`new_page` will match the spec, and yet `new_page` itself hasn't changed. Nor has its 'presence' - it was present +before and it is present now. Should this cause a re-build of any page that has a 'presence' dependency on the spec? + +> 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. 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. + +In the longer term I was thinking we'd have to introduce a concept of 'internal pagespec dependencies'. Note that I'm +defining 'internal' pagespec dependencies differently to the pagespec dependencies I defined above. Perhaps an example: +If you had a pagespec that was `created_before(test_page)`, then you could list all pages created before `test_page` +with a `map` directive. The map directive would add a pagespec dependency on `created_before(test_page)`. +Internally, there would be a second page-spec parsing function that discovers which pages a given pagespec +depends on. As well as the function `match_created_before()`, we'd have to add a new function `depend_created_before()`. +This new function would return a list of pages, which when any of them change, the output of `match_created_before()` +would change. In this example, it would just return `test_page`. + +These lists of dependent pages could just be concatenated for every `match_...()` function in a pagespec - you can ignore +the boolean formula aspects of the pagespec for this. If a content dependency were added on these pages, then I think +the correct rebuilds would occur. + +In all, this is a surprisingly difficult problem to solve perfectly. Consider the following case: + +PageA.mdwn: + +> [ShavesSelf] + +PageB.mdwn + +> Doesn't shave self. + +ShavedByBob.mdwn: + +> [!include pages="!link(ShavesSelf)"] + +Does ShavedByBob.mdwn include itself? + +(Yeah - in IkiWiki currently links are included by include, but the idea holds. I had a good example a while back, but I can't think of it right now.) + +sigh. + +-- [[Will]] + +> 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. More thoughts on influence lists a bit below. --[[Joey]] + +---- + +### Link dependencies + +* `add_depends($page, $spec, links => 1, presence => 1)` + adds a links + presence dependency. +* Use backlinks change code to detect changes to link dependencies too. +* So, brokenlinks can fire whenever any links in any of the + pages it's tracking change, or when pages are added or + removed. +* To determine if a pagespec is valid to be used with a links dependency, + use the same set that are valid for presence dependencies. But also + allow `backlinks()` to be used in it, since that matches pages + that the page links to, which is just what link dependencies are + triggered on. + +[[done]] +---- + +### the removal problem + +So far I have not addressed fixing the removal problem (which Will +discusses above). + +Summary of problem: A has a dependency on a pagespec such as +"bugs/* and !link(done)". B currently matches. Then B is updated, +in a way that makes A's dependency not match it (ie, it links to done). +Now A is not updated, because ikiwiki does not realize that it +depended on B before. + +This was worked around to fix [[bugs/inline_page_not_updated_on_removal]] +by inline and map adding explicit dependencies on each page that appears +on them. Then a change to B triggers the explicit dep. While this works, +it's 1) ugly 2) probably not implemented by all plugins that could +be affected by this problem (ie, linkmap) and 3) is most of the reason why +we grew the complication of `depends_simple`. + +One way to fix this is to include with each dependency, a list of pages +that currently match it. If the list changes, the dependency is triggered. + +Should be doable, but may involve more work than +currently. Consider that a dependency on "bugs/*" currently +is triggered by just checking until *one* page is found to match it. +But to store the list, *every* page would have to be tried against it. +Unless the list can somehow be intelligently updated, looking at only the +changed 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. + +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.