From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Gierth <andrew@tao11.riddles.org.uk>
cc: pgsql-bugs@postgresql.org
Subject: Re: BUG #14487: malformed empty array from array_fill
In-reply-to: <874m1d1q1b.fsf@news-spur.riddles.org.uk>
References: <20170105152156.10135.64195@wrigleys.postgresql.org>
 <874m1d1q1b.fsf@news-spur.riddles.org.uk>
Comments: In-reply-to Andrew Gierth <andrew@tao11.riddles.org.uk>
	message dated "Thu, 05 Jan 2017 15:33:19 +0000"
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Date: Thu, 05 Jan 2017 10:55:13 -0500
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Andrew Gierth <andrew@tao11.riddles.org.uk> writes:
> "andrew" == andrew  <andrew@tao11.riddles.org.uk> writes:
>  andrew> array_fill returns a malformed empty array when given a size of
>  andrew> zero:

> Also, why does array_fill reject the case of an empty array of
> dimensions?  It seems obvious that it should return an empty array
> result in such cases.

Yeah.  The code seems to have been intending to allow that:

	ndims = ARR_DIMS(dims)[0];

	if (ndims < 0)				/* we do allow zero-dimension arrays */

but it doesn't work right, precisely because that case comes out
as being zero-dimensional not one dimension of length 0.

Ideally I think we would reject zeroes in the lengths array as being an
error, but it's probably too late for that, because likely people are
using array[0] to get an empty result array since '{}' doesn't work.

It also strikes me that this restriction is quite pointless:

	if (ARR_LBOUND(dims)[0] != 1)
		ereport(ERROR,
				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
				 errmsg("wrong range of array subscripts"),
				 errdetail("Lower bound of dimension array must be one.")));

I think it's reasonable to disallow multi-dimensional input arrays here,
but I don't see why it matters what the LB is.

			regards, tom lane


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