Should cast to CHAR or NUMERIC enforce default length limit?

Now that I've modified the code so that casting to a specific length
actually works --- ie you can dox :: char(7)CAST (y AS numeric(40,6))
and get the expected results --- I am starting to worry that there
may be unwanted side-effects.  The reason is that the system by default
interprets "char" as "char(1)" and "numeric" as "numeric(30,6)".
So if you just write "x::char" you will now get truncation to one
character, which did not use to happen.  Another distressing example
is
regression=# select '123456789012345678901234567890.12'::numeric;
ERROR:  overflow on numeric ABS(value) >= 10^29 for field with precision 30 scale 6
which I think is arguably a violation of the SQL standard --- it says
pretty clearly that the precision and scale of a numeric constant are
whatever is implicit in the number of digits.

I am inclined to think that in the context of a cast, we shouldn't
enforce a coercion to default length, but should only coerce if a length
is explicitly specified.  This would change the behavior of "x::char"
back to what it was.

I think this could be done by having gram.y insert -1 as the default
typmod for a "char" or "numeric" Typename.  The rest of the system
already interprets such a typmod as specifying no particular length
constraint.  Then, to preserve the rule thatcreate table foo (bar char);
creates a char(1) field, analyze.c would have to be responsible for
inserting the appropriate default length in place of -1 when processing
a column definition.

Comments?  Better ideas?
        regards, tom lane