X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/d8607f5e73990e7802e03eef2065ebac102fbd2f..a09c79ccf1b9523c4b82db8846435c81f7404d44:/doc/todo/dependency_types.mdwn diff --git a/doc/todo/dependency_types.mdwn b/doc/todo/dependency_types.mdwn index 7e940543c..7714f2891 100644 --- a/doc/todo/dependency_types.mdwn +++ b/doc/todo/dependency_types.mdwn @@ -156,6 +156,90 @@ 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 [[!template id=gitbranch branch=origin/depends-spec author="[[will]]"]] +That branch is a little out of date, but if you just look at the changes in IkiWiki.pm you'll see the concept I was looking at.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. --[[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. 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]] + ---- ### Link dependencies @@ -198,9 +282,41 @@ 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 seems to involve a more work than +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. +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. + +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. + +---- + +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 presense +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.