Re: BUG #8399: inconsistent input of multidimensional arrays

On Tue, Aug 27, 2013 at 08:18:10AM +0000, borz_off(at)cs(dot)msu(dot)su wrote:
> PostgreSQL documentation states:
>
>
> "Multidimensional arrays must have matching extents for each dimension. A
> mismatch causes an error..."
>
>
> This is not completely true:
> postgres=# select cast('{{1,2}, {3}}' as integer[]);
> ERROR: multidimensional arrays must have array expressions with matching
> dimensions
> LINE 1: select cast('{{1,2}, {3}}' as integer[]);
> ^
> postgres=# select cast('{{1}, {2,3}}' as integer[]);
> int4
> ------------------
> {{1,NULL},{2,3}}
> (1 row)
>
>
> Trying to use an array constructor yields an expected error in both cases.
>
>
> Confirmed on 9.3rc1 and 9.0.13

This is a very interesting report. The behavior you are seeing is based
on this 2004 commit:

commit 0e13d627bebad769498696b5fd0ac821bde5140d
Author: Joe Conway <mail(at)joeconway(dot)com>
Date: Thu Aug 5 03:30:44 2004 +0000

Require that array literals produce "rectangular" arrays, i.e. all the
subarrays of a given dimension have the same number of elements/subarrays.

Also repair a longstanding undocumented (as far as I can see) ability to
explicitly set array bounds in the array literal syntax. It now can
deal properly with negative array indicies. Modify array_out so that
arrays with non-standard lower bounds (i.e. not 1) are output with
the expicit dimension syntax. This fixes a longstanding issue whereby
arrays with non-default lower bounds had them changed to default
after a dump/reload cycle.

Modify regression tests and docs to suit, and add some minimal
documentation regarding the explicit dimension syntax.

Particularly, this block of code:

if ((nelems_last[nest_level] != 1) &&
(nelems[nest_level] != nelems_last[nest_level]))
ereport(ERROR,
(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
errmsg("multidimensional arrays must have "
"array expressions with matching "
"dimensions")));

The nelems_last array is initialized to '1', so when an array comes in
that is one element, no check is made. I doubt this was intended.

What I have done is to change the initalization and test to -1, which
seems to fix the problem.

test=> select cast('{{1}, {2, 3}}' as integer[]);
ERROR: multidimensional arrays must have array expressions with matching dimensions
LINE 1: select cast('{{1}, {2, 3}}' as integer[]);

I was a little worried that this might break existing values stored in
the database, and hence dump/reload, but it seems the arrays are
extended with NULLs so it loads just fine:

CREATE TABLE test(x int[]);
INSERT INTO test SELECT cast('{{1}, {2, 3, 4, 5}}' AS integer[]);
COPY test TO stdout;
{{1,NULL,NULL,NULL},{2,3,4,5}}

Patch attached. The patch controls what strings are accepted as arrays
and will be an incompatibility for 9.4.

Joe, does this sound right?

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

+ Everyone has their own god. +