I wrote:
> Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
>> Marking textanycat as not immutable would forbid using it in
>> expression indexes, too.
> True. On the other hand, the current state of affairs allows one to
> create an index on expressions that aren't really immutable, with
> ensuing hilarity.
It strikes me that we could avoid any possible functional regression
here by having CREATE INDEX perform expression preprocessing (in
particular, function inlining) before it tests to see if the index
expression contains any non-immutable functions.
regards, tom lane