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[ikiwiki.git] / doc / bugs / conditional_preprocess_during_scan.mdwn

diff --git a/doc/bugs/conditional_preprocess_during_scan.mdwn b/doc/bugs/conditional_preprocess_during_scan.mdwn
index 896998bf8226fecee343faab3f1cdd58ac181584..1ba142331dd0804b63a25f6d3c48d171c8f5ef00 100644 (file)
--- a/doc/bugs/conditional_preprocess_during_scan.mdwn
+++ b/doc/bugs/conditional_preprocess_during_scan.mdwn
@@ -1,4 +1,4 @@
-[[!template id=gitbranch branch=GiuseppeBilotta/scanif author="Giuseppe Bilotta"]]
+[[!template id=gitbranch branch=GiuseppeBilotta/scanif author="[[GiuseppeBilotta]]"]]
 
 When a directive that should be run during scan preprocessing is inside
 an if directive, it doesn't get called because the if preprocessing does
@@ -8,3 +8,50 @@ I've written a simple [[patch]] to fix the issue, currently hosted on the
 scanif branch of my repository. The patch also passes the preview option
 back to the Ikiwiki::preprocess call, making sure that whatever is being
 reprocessed is done so in the same conditions as the original call.
+
+> One problem with this is that it has the same dependency-ordering problems
+> as inline-based or pagespec-based trails with my [[plugins/contrib/trail]]
+> plugin: `if` takes a pagespec, but pagespecs aren't guaranteed to match
+> correctly until everything has been scanned (for instance, `link()` might
+> give the wrong results because a page that added or deleted a link hasn't
+> been scanned yet). If you have a clever idea for how to fix this, I'd love
+> to hear it - being able to specify a [[plugins/contrib/trail]] in terms
+> of a sorted pagespec would be useful. --[[smcv]]
+
+>> I have a solution to the dependency-ordering problem in a different
+>> branch of my repository, with a post_scan hook mechanism which I use to
+>> be able to sort outer inline pages according to the last modification
+>> date of their nested inline pages. The way I implemented it currently,
+>> though, doesn't use the existing hooks mechanism of ikiwiki (because
+>> it's something which I believe to be more efficiently done the way I
+>> implemented it) so I don't know how likely it is to be included
+>> upstream.
+
+>> For what it's worth, I think that my post_scan hook mechanism would work
+>> rather fine with your trail plugin.
+
+>>> We discussed this on IRC, and I think it's actually more complicated
+>>> than that: the branch to sort by newest inlined entry wants a
+>>> "pagespecs now work" hook, whereas for trail I want a "sorting now
+>>> works" hook:
+>>>
+>>> * scan
+>>> * pagespecs now work (post-scan)
+>>>   * Giuseppe's version of inline can decide what each inline
+>>>     contains, and thus decide where they go in `inline(mtime)`
+>>>     order
+>>> * pagespecs and sorting now work (pre-render)
+>>>   * my trail plugin can decide what each trail contains, and
+>>>     also sort them in the right order (which might be
+>>>     `inline(mtime)`, so might be undefined until pagespecs work)
+>>> * render
+>>>
+>>> --[[smcv]]
+
+>> However, the case of the if
+>> directive is considerably more complicated, because the conditional
+>> can introduce a much stronger feedback effect in the pre/post scanning
+>> dependency. In fact, it's probably possible to build a couple of pages
+>> with vicious conditional dependency circles that would break/unbreak
+>> depending on which pass we are in. And I believe this is an intrinsic
+>> limitation of the system, which cannot be solved at all.