Re: Inconsistent error message for varchar(n)

Japin Li <japinli(at)hotmail(dot)com> writes:
> postgres=# CREATE TABLE tbl (s varchar(2147483647));
> ERROR: length for type varchar cannot exceed 10485760
> LINE 1: CREATE TABLE tbl (s varchar(2147483647));
> ^

> postgres=# CREATE TABLE tbl (s varchar(2147483648));
> ERROR: syntax error at or near "2147483648"
> LINE 1: CREATE TABLE tbl (s varchar(2147483648));
> ^

I'm having a very hard time getting excited about that. We could maybe
switch the grammar production to use generic expr_list syntax for the
typmod, like GenericType does. But that would just result in this:

regression=# CREATE TABLE tbl (s "varchar"(2147483648));
ERROR: value "2147483648" is out of range for type integer
LINE 1: CREATE TABLE tbl (s "varchar"(2147483648));
^

which doesn't seem any less confusing for a novice who doesn't know
that typmods are constrained to be integers.

There might be something to be said for switching all the hard-wired
type productions to use opt_type_modifiers and pushing the knowledge
that's in, eg, opt_float out to per-type typmodin routines. But any
benefit would be in reduction of the grammar size, and I'm dubious
that it'd be worth the trouble. I suspect that overall, the resulting
error messages would be slightly worse not better --- note for example
the poorer placement of the error cursor above. A related example is

regression=# CREATE TABLE tbl (s varchar(2,3));
ERROR: syntax error at or near ","
LINE 1: CREATE TABLE tbl (s varchar(2,3));
^
regression=# CREATE TABLE tbl (s "varchar"(2,3));
ERROR: invalid type modifier
LINE 1: CREATE TABLE tbl (s "varchar"(2,3));
^

That's explained by the comment in anychar_typmodin:

* we're not too tense about good error message here because grammar
* shouldn't allow wrong number of modifiers for CHAR

and we could surely improve that message, but anychar_typmodin can't give
a really on-point error cursor.

regards, tom lane