inconsistent between the one-and two-argument forms. Thoughts?
--[[smcv]]
+
+> I've applied the branch as-is, so this bug is [[done]].
+> `prune` is not an exported API so changing it would be ok..
+> I think required 2-argument would be better, but have not checked
+> all the call sites to see if the `$file` is available split out
+> as that would need. --[[Joey]]
+
+[[!template id=gitbranch branch=smcv/ready/prune author="[[Simon McVittie|smcv]]"]]
+
+>> Try this, then? I had to make some changes to `attachment`
+>> to make the split versions available. I suggest reviewing
+>> patch-by-patch.
+
+>>> Branch updated; I'd missed a use of prune in ikiwiki.in itself.
+>>> Unfortunately, this means it does still need to support the
+>>> "undefined top directory" case: there isn't an obvious top
+>>> directory for wrappers. --[[smcv]]
+
+>> I also tried to fix a related bug which I found while testing it:
+>> the special case for renaming held attachments didn't seem to work.
+>> (`smcv/wip/rename-held`.) Unfortunately, it seems that with that
+>> change, the held attachment is committed to the `srcdir` when you
+>> rename it, which doesn't seem to be the intention either? --[[smcv]]