Preliminary support, anyway.
If a dependency only includes DEPEND_EXISTS, then only changes that
involved adding or deleting a page can trigger it.
This is complicated by internal pages, since the code did not previously
differentiate between add, delete, and change of internal pages.
Now it tracks change separately from add+delete, so DEPEND_EXISTS pagespecs
that actually match internal pages (which will probably be quite rare in
practice) should work.
Dependency types are represented by bits in the values of the %depends
and %depends_simple hashes.
Change the dependslist array saved to the index to a depends hash.
depends_simple is also converted from an array to a hash.
Note that the depends field used to be a string, and we still
have compat code to handle upgrades from that, as well as from the arrays.
I didn't use ikiwiki-transition because I don't want ikiwiki to break if
users forget to run it; also we're going to recommend a full rebuild on
upgrade to this version to get the improved dependency handling. So
this compat code can be removed or moved to ikiwiki-transition later.
Here I was bitten by perl's aliasing of foreach variables
to the loop array contents, and match_link accidentially changed
the contents of %links.
In Jon's testcase, a tag added an absolute link, which was
made relative by the above bug, and then the link was added
again in preprocess, and turned into a duplicate.
As soon as a change happens, we know we will need to rescan all
dependencies from the start, so bail out of the current scan partway to
avoid doing redundant work.
Only problem with this is that ikiwiki sometimes ends up printing out
dependencies that, while correct, are not obvious. Before:
building B, which depends on A
building C, which depends on A
building D, which depends on A
After:
building B, which depends on A
building C, which depends on B
building D, which depends on C