to_date() marked stable?

I was wondering why we mark to_date() as stable and not immutable? It
seems to have been set to stable in 2006 with this patch:

http://archives.postgresql.org/pgsql-committers/2006-11/msg00264.php

Also, mark to_date() and to_char(interval) as stable; although these
appear not to depend on any GUC variables as of CVS HEAD, that seems a
property unlikely to survive future improvements. It seems best to mark
all the formatting functions stable and be done with it.

Are there people using to_date in indexes or partition functions where
changing it to immutable would be useful? The code seems complete
enough now that we should consider an optimization here.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +