Re: Inconsistent error message for varchar(n)

On Sun, Nov 14, 2021 at 10:33:19AM +0800, Japin Li wrote:
>
> On Sat, 13 Nov 2021 at 23:42, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > 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.
> >
>
> Oh! I didn't consider this situation. Since the max size of varchar cannot
> exceed 10485760, however, I cannot find this in documentation [1]. Is there
> something I missed? Should we mention this in the documentation?
>
> [1] https://www.postgresql.org/docs/devel/datatype-character.html

Sorry for my long delay in reviewing this issue. You are correct this
should be documented --- patch attached.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

Indecision is a decision. Inaction is an action. Mark Batterson