Last modified: 2006-02-25 00:18:02 UTC
If a page ([[A]]) includes a template ("{{B}}"), and that template includes another template ("{{C}}"), (so the content of [[Template:C]] is visible when viewing [[A]]), a change to [[Template:C]] will not be visible on [[A]] until the cache is manually purged. This is because the Template code only purges the cache for pages which have 'links' entries pointing to [[Template:C]], and [[A]] is not listed there. If, as suggested at bug 734, there was a seperate database table for inclusions, the section of Article.php that handles the purging (in updateArticle()) could be made to do the purging "recursively". In fact, actual recursion is unnecessary, we just need 2 lists: "$open" and "$closed"; pseudo-code follows (omitting boring bits like converting objects to and from strings): $open = $this->getInclusionsTo(); while(! is_empty($open) ) { $next=pop($open); if(isset(($closed[$next])) { continue; } # do each only once $closed[$next] = true; array_merge($open, $next->getInclusionsTo()); $pages_to_purge[] = $next; # actually, the array is called "$urls" currently } An alternative solution is to record a link in the database [again, preferably in an 'inclusionlinks' table] between [[A]] and [[Template:C]] when [[A]] includes {{B}} and [[Template:B]] includes {{C}}. (I tried to work out what it is that stops this happening already; but I couldn't understand the code well enough, and gave up. Is it a deliberate behaviour, or just a product of the way recursive templates are handled?) This would of course have the side-effect of [[A]] appearing on a Whatlinkshere-type list of "pages which include [[Template:C]]", but perhaps this would be a good thing, since, visually, it does.
It looks like separating the "links" table and the "transcludes" table is the cleanest solution, any other would be a kludge. Mixing the two tables might have more bugs not yet found, which might require more changes, and soon the code might become a mess. Just as we have separate "categorylinks" and "imagelinks" tables (according to bug 939 comment 3), we should have a "templatelinks" table as well. This allows {{foo}} and [[Template:foo]] to be treated differently, just like [[Category:foo]] and [[:Category:foo]] are treated separately, and [[Image:foo]] and [[:Image:foo]] are treated separately. Disclaimer: I haven't looked at the code. This is just my intuition.
This also affects Categorys as described, only there isn't an automatic way of clearing the cache of a category.
*** Bug 4440 has been marked as a duplicate of this bug. ***
The issue is fixed in CVS for 1.6 release. Recursive purging would be slow, and wouldn't work for template links created by template arguments, e.g. a: {{b|some page}} b: {{ {{{1}}} }} That's why I chose to register all templates loaded during a parse in the templatelinks table. This provides good caching behaviour at the expense of perhaps counterintuitive Special: Whatlinkshere results.
