Re: ltree::text not immutable?

I wrote:
>> More generally, it seems like we ought to have a test in the type_sanity
>> regression script that checks that type I/O functions aren't volatile,
>> ...

> Actually, the right thing to do if we want to enforce this is for
> CREATE TYPE to check the marking. We'd still need a type_sanity
> test to check erroneous declarations of built-in types, but a complaint
> in CREATE TYPE would cover all the contrib modules as well as third-party
> code.

> I wouldn't propose back-patching such an error check, but it seems
> reasonable to add it for 9.5. Any objections?

On the way to fixing this, I was unpleasantly surprised to discover that
we have one I/O function in contrib that *actually is* volatile, and not
just thoughtlessly marked that way. That's chkpass_in(), which is
volatile because it goes to the trouble of using random() to produce a
new password salt value on every call.

Not entirely sure what to do about this. It seems like for the purposes
of contrib/chkpass, it's a good thing that chkpass_in() won't reuse the
same salt. Weak as a 12-bit salt might be nowadays, it's still better
than no salt. Nonetheless, this behavior is breaking assumptions made
in places like array_in and record_in.

For the moment I'm tempted to mark chkpass_in as stable (with a comment
explaining that it isn't really) just so we can put in the error check
in CREATE TYPE. But I wonder if anyone has a better idea.

regards, tom lane