Fix plpgsql's exec_move_row() to supply valid type OIDs to exec_assign_value()

whenever possible, as per bug report from Oleg Serov.  While at it, reorder
the operations in the RECORD case to avoid possible palloc failure while the
variable update is only partly complete.

Back-patch as far as 8.1.  Although the code of the particular function is
similar in 8.0, 8.0's support for composite fields in rows is sufficiently
broken elsewhere that it doesn't seem worth fixing this.

src/pl/plpgsql/src/pl_exec.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.218 2008/08/29 13:02:33 petere Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.219 2008/09/01 22:30:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -4513,13 +4513,27 @@ exec_move_row(PLpgSQL_execstate *estate,
 	if (rec != NULL)
 	{
 		/*
-		 * copy input first, just in case it is pointing at variable's value
+		 * Copy input first, just in case it is pointing at variable's value
 		 */
 		if (HeapTupleIsValid(tup))
 			tup = heap_copytuple(tup);
+		else if (tupdesc)
+		{
+			/* If we have a tupdesc but no data, form an all-nulls tuple */
+			char	   *nulls;
+
+			nulls = (char *) palloc(tupdesc->natts * sizeof(char));
+			memset(nulls, 'n', tupdesc->natts * sizeof(char));
+
+			tup = heap_formtuple(tupdesc, NULL, nulls);
+
+			pfree(nulls);
+		}
+
 		if (tupdesc)
 			tupdesc = CreateTupleDescCopy(tupdesc);
 
+		/* Free the old value ... */
 		if (rec->freetup)
 		{
 			heap_freetuple(rec->tup);
@@ -4531,24 +4545,12 @@ exec_move_row(PLpgSQL_execstate *estate,
 			rec->freetupdesc = false;
 		}
 
+		/* ... and install the new */
 		if (HeapTupleIsValid(tup))
 		{
 			rec->tup = tup;
 			rec->freetup = true;
 		}
-		else if (tupdesc)
-		{
-			/* If we have a tupdesc but no data, form an all-nulls tuple */
-			char	   *nulls;
-
-			nulls = (char *) palloc(tupdesc->natts * sizeof(char));
-			memset(nulls, 'n', tupdesc->natts * sizeof(char));
-
-			rec->tup = heap_formtuple(tupdesc, NULL, nulls);
-			rec->freetup = true;
-
-			pfree(nulls);
-		}
 		else
 			rec->tup = NULL;
 
@@ -4568,7 +4570,7 @@ exec_move_row(PLpgSQL_execstate *estate,
 	 * attributes of the tuple to the variables the row points to.
 	 *
 	 * NOTE: this code used to demand row->nfields ==
-	 * HeapTupleHeaderGetNatts(tup->t_data, but that's wrong.  The tuple might
+	 * HeapTupleHeaderGetNatts(tup->t_data), but that's wrong.  The tuple might
 	 * have more fields than we expected if it's from an inheritance-child
 	 * table of the current table, or it might have fewer if the table has had
 	 * columns added by ALTER TABLE. Ignore extra columns and assume NULL for
@@ -4580,6 +4582,7 @@ exec_move_row(PLpgSQL_execstate *estate,
 	 */
 	if (row != NULL)
 	{
+		int			td_natts = tupdesc ? tupdesc->natts : 0;
 		int			t_natts;
 		int			fnum;
 		int			anum;
@@ -4602,12 +4605,18 @@ exec_move_row(PLpgSQL_execstate *estate,
 
 			var = (PLpgSQL_var *) (estate->datums[row->varnos[fnum]]);
 
-			while (anum < t_natts && tupdesc->attrs[anum]->attisdropped)
+			while (anum < td_natts && tupdesc->attrs[anum]->attisdropped)
 				anum++;			/* skip dropped column in tuple */
 
-			if (anum < t_natts)
+			if (anum < td_natts)
 			{
+				if (anum < t_natts)
 					value = SPI_getbinval(tup, tupdesc, anum + 1, &isnull);
+				else
+				{
+					value = (Datum) 0;
+					isnull = true;
+				}
 				valtype = SPI_gettypeid(tupdesc, anum + 1);
 				anum++;
 			}