Re: strpos behavior change around empty substring in PG12

Thanks for the quick turnaround!

Tom Lane <tgl@sss.pgh.pa.us> schrieb am Mo., 28. Okt. 2019, 16:57:

> Robert Haas <robertmhaas@gmail.com> writes:
> > On Mon, Oct 28, 2019 at 11:02 AM Shay Rojansky <roji@roji.org> wrote:
> >> Before PG12, select strpos('test', '') returns 1 (empty substring found
> at first position of the string), whereas starting with PG12 it returns 0
> (empty substring not found).
>
> > It looks to me like this got broken here:
>
> > commit 9556aa01c69a26ca726d8dda8e395acc7c1e30fc
> > Author: Heikki Linnakangas <heikki.linnakangas@iki.fi>
> > Date:   Fri Jan 25 16:25:05 2019 +0200
> >     Use single-byte Boyer-Moore-Horspool search even with multibyte
> encodings.
>
> > Not sure what happened exactly.
>
> I think the problem is lack of clarity about the edge cases.
> The patch added this short-circuit right at the top of text_position():
>
> +   if (VARSIZE_ANY_EXHDR(t1) < 1 || VARSIZE_ANY_EXHDR(t2) < 1)
> +       return 0;
>
> and as this example shows, that's the Wrong Thing.  Fortunately,
> it also seems easily fixed.
>
>                         regards, tom lane
>