Re: BUG #16325: Assert failure on partitioning by int for a textvalue with a collation

> On Wed, Apr 01, 2020 at 04:08:42PM +0900, Michael Paquier wrote:
> > On Sat, Mar 28, 2020 at 01:53:03PM +0100, Dmitry Dolgov wrote:
> > Thanks for reporting! Looks like transformPartitionBoundValue needs to
> > check that the source collumn is collatable, then we get more expected
> > result:
> >
> >     =# create table part_coll partition of parted for values in ('1' collate "POSIX");
> >     ERROR:  42804: collations are not supported by type integer
>
> We have here a side effect of 7c079d74, that has given the possibility
> to pass down general expressions for partition bounds.

Yep. That's why I've placed a test for this fix close to those
introduced in this commit.

> > +        if (type_is_collatable(colType))
> > +        {
> > +            if (!OidIsValid(exprCollOid))
> > +                ereport(ERROR,
> > +                        (errcode(ERRCODE_INDETERMINATE_COLLATION),
> > +                         errmsg("could not determine which collation to use for partition expression"),
> > +                         errhint("Use the COLLATE clause to set the collation explicitly.")));
> > +        }
> > +        else
> > +        {
> > +            if (OidIsValid(exprCollOid))
> > +                ereport(ERROR,
> > +                        (errcode(ERRCODE_DATATYPE_MISMATCH),
> > +                         errmsg("collations are not supported by type %s",
> > +                                format_type_be(colType))));
> > +        }
> > +
>
> It seems to me that the first error cannot happen, and should not
> happen.  When the expression is transformed, there is a lookup at the
> collation used via transformCollateClause() -> LookupCollation() ->
> get_collation_oid() which would never return an invalid OID if the
> collation exists, throwing an error instead.  The reason why a similar
> check exists in tablecmds.c is that there can be a collation override,
> no?

Good point, I believe you're right. This means that the fix can be
reduced as in attachments.