PostGIS 3.2.0: ST_StartPoint with empty geometries

[ezimanyi]

While performing the regression tests for MobilityDB with the latest version PostGIS 3.2.0 we found out that maybe the function LWGEOM_startpoint_linestring should test whether the argument is empty. Although the function correctly outputs a NULL value for empty geometries, it throws an error message as follows

test=# select ST_StartPoint(geometry 'linestring empty');
NOTICE:  lwgeom_api.c [138] called with n=0 and npoints=0
 st_startpoint
---------------

(1 row)

It may be useful to test whether the input geometry is empty before calling lwgeom_from_gserialized as suggested below.

Datum LWGEOM_startpoint_linestring(PG_FUNCTION_ARGS)
{
  GSERIALIZED *geom = PG_GETARG_GSERIALIZED_P(0);
  /* BEGIN NEW TEST */
  if (gserialized_is_empty(geom))
  {
    PG_RETURN_NULL();
  }
  /* END NEW TEST */
  
  GSERIALIZED *ret;
  LWGEOM *lwgeom = lwgeom_from_gserialized(geom);
  LWGEOM *lwpoint = NULL;
  POINT4D pt;

  if (lwgeom_startpoint(lwgeom, &pt) == LW_FAILURE)
  {
    PG_RETURN_NULL();
  }
  [...]
}

[robe]

This looks like a debug message left in, not an error one. I confirm I see it too.

[Paul Ramsey <pramsey@…>]

In a05bf507/git:

Test for empty before reading start point. Closes #5036

[Paul Ramsey <pramsey@…>]

In 49ee0d4/git:

Test for empty before reading start point. Closes #5036

[Paul Ramsey <pramsey@…>]

In 49ee0d4/git:

Test for empty before reading start point. Closes #5036