Re: Inconsistent error message for varchar(n)

On Sat, 13 Nov 2021 at 23:42, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Japin Li <japinli@hotmail.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

-- 
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.