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| -rw-r--r-- | doc/todo/tracking_bugs_with_dependencies.mdwn | 61 |
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diff --git a/doc/todo/tracking_bugs_with_dependencies.mdwn b/doc/todo/tracking_bugs_with_dependencies.mdwn index 417d5910e..ac57965ef 100644 --- a/doc/todo/tracking_bugs_with_dependencies.mdwn +++ b/doc/todo/tracking_bugs_with_dependencies.mdwn @@ -310,6 +310,10 @@ account all comments above (which doesn't mean it is above reproach :) ). --[[W >>> it shouldn't (but I haven't verified that really happens). >>> That could certianly be a show-stopper. --[[Joey]] +>>>> Even if that works, this is a good argument for having a syntactic difference between named pagespecs and normal pages. +>>>> If you're joining two pagespecs with 'or', you don't want a named pagespec in the first part overriding a page name in the +>>>> second part. Oh, and I assume 'or' has the right operator precedence that "a and b or c" is "(a and b) or c", and not "a and (b or c)" -- [[Will]] + >> Secondly, it seems that there are two types of dependency, and ikiwiki >> currently only handles one of them. The first type is "Rebuild this >> page when any of these other pages changes" - ikiwiki handles this. @@ -328,6 +332,63 @@ account all comments above (which doesn't mean it is above reproach :) ). --[[W >>>> case though and I'll be suprised if they fit well into pagespecs. >>>> --[[Joey]] +>>>>> The issue is that the existential pagespec matching allows you to build things that have similar +>>>>> problems to backlinks. +>>>>> e.g. the following inline: + + \[[!inline pages="define(~done, link(done)) and link(~done)" archive=yes]] + +>>>>> includes any page that links to a page that links to done. Now imagine I add a new link to 'done' on +>>>>> some random page somewhere - a page which some other page links to which didn't previously get included - the set of pages accepted by the pagespec, and hence the set of +>>>>> pages inlined, will change. But, there is no dependency anywhere on the page that I altered, so +>>>>> ikiwiki will not rebuild the page with the inline in it. What is happening is that the page that I altered affects +>>>>> the set of pages matched by the pagespec without itself being matched by the pagespec, and hence included in the dependency list. + +>>>>> For another example, imagine I added a `match_word()` function. It matches any page that contains the given word. As with a backlink, +>>>>> it is now possible to change the set of pages referred to by a pagespec without changing any of the pages currently referred to by the +>>>>> pagespec. If I have an inline of all pages that include the word "abracadabra", then it would have to depend upon all pages to detect +>>>>> any new uses of that word. + +>>>>> To make this work well, I think you need to recognise two types of dependencies for each page (and no +>>>>> special cases for particular types of links, eg backlinks). The first type of dependency says, "The content of +>>>>> this page depends upon the content of these other pages". The `add_depends()` in the shortcuts +>>>>> plugin is of this form: any time the shortcuts page is edited, any page with a shortcut on it +>>>>> is rebuilt. The inline plugin also needs to add dependencies of this form to detect when the inlined +>>>>> content changes. By contrast, the map plugin does not need a dependency of this form, because it +>>>>> doesn't actually care about the content of any pages, just which pages it needs to include (which we'll handle next). + +>>>>> The second type of dependency says, "The content of this page depends upon the exact set of pages matched +>>>>> by this pagespec". The first type of dependency was about the content of some pages, the second type is about +>>>>> which pages get matched by a pagespec. This is the type of dependency tracking that the map plugin needs. +>>>>> If the set of pages matched by map pagespec changes, then the page with the map on it needs to be rebuilt to show a different list of pages. +>>>>> Inline needs this type of dependency as well as the previous type - This type handles a change in which pages +>>>>> are inlined, the previous type handles a change in the content of any of those pages. Shortcut does not need this type of +>>>>> dependency. Most of the places that use `add_depends()` seem to need this type of dependency rather than the first type. + +>>>>> Implementation Details: The first type of dependency can be handled very similarly to the current +>>>>> dependency system. You just need to keep a list of pages that the content depends upon. You could +>>>>> keep that list as a pagespec, but if you do this you might want to check that the pagespec doesn't change, +>>>>> possibly by adding a dependency of the second type along with the dependency of the first type. + +>>>>> The second type of dependency is a little more tricky. For each page, we'd need a list of pagespecs that +>>>>> the page depended on, and for each pagespec you'd want to store the list of pages that currently match it. +>>>>> On refresh, you'd need to check each pagespec to see if the set of pages that match it has changed, and if +>>>>> that set has changed, then rebuild the dependent page(s). Oh, and for this second type of dependency, I +>>>>> don't think you can merge pagespecs. If I wanted to know if either "*" or "link(done)" changes, then just checking +>>>>> to see if the set of pages matched by "* or link(done)" changes doesn't work. + +>>>>> The current system works because even though you usually want dependencies of the second type, the set of pages +>>>>> referred to by a pagespec can only change if one of those pages itself changes. i.e. A dependency check of the +>>>>> first type will catch a dependency change of the second type with current pagespecs. +>>>>> This doesn't work with backlinks, and it doesn't work with existential matching. Backlinks are currently special-cased. I don't know +>>>>> how to special-case existential matching - I suspect you're better off just getting the dependency tracking right. + +>>>>> I also tried to come up with other possible solutions: e.g. can we find the dependencies for a pagespec? That +>>>>> would be the set of pages where a change on one of those pages could lead to a change in the set of pages matched by the pagespec. +>>>>> For old-style pagespecs without backlinks, the dependency set for a pagespec is the same as the set of pages the pagespec matches. +>>>>> Unfortunately, with existential matching, the set of pages that each +>>>>> pagespec depends upon can quickly become "*", which is not very useful. -- [[Will]] + ---- diff --git a/IkiWiki.pm b/IkiWiki.pm |