BUG #1922: bit string of calculated length

The following bug has been logged online:

Bug reference: 1922
Logged by: Sorin Schwimmer
Email address: sxn02(at)yahoo(dot)com
PostgreSQL version: 8.0.2
Operating system: Gentoo Linux 2005
Description: bit string of calculated length
Details:

When puting in an expression something like
'0'::BIT(20-LENGTH(something_here))
I receive an error message suggesting that integer arithmetic is not allowed
in a BIT declaration.
The following experiments should prove my point:
SELECT '0'::BIT(20-4);
SELECT '0'::BIT(10+2);

I'd like to suggest to allow for any expression that converts to positive
integer.

Thanks,
Sorin Schwimmer