Allow zero-dimensional (ie, empty) arrays in contrib/ltree operations.

The main motivation for changing this is bug #4921, in which it's pointed out
that it's no longer safe to apply ltree operations to the result of
ARRAY(SELECT ...) if the sub-select might return no rows.  Before 8.3,
the ARRAY() construct would return NULL, which might or might not be helpful
but at least it wouldn't result in an error.  Now it returns an empty array
which results in a failure for no good reason, since the ltree operations
are all perfectly capable of dealing with zero-element arrays.

As far as I can find, these ltree functions are the only places where zero
array dimensionality is rejected unnecessarily.

Back-patch to 8.3 to prevent behavioral regression of queries that worked
in older releases.

contrib/ltree/_ltree_gist.c

 /*
- * $PostgreSQL: pgsql/contrib/ltree/_ltree_gist.c,v 1.26 2009/06/11 14:48:51 momjian Exp $
+ * $PostgreSQL: pgsql/contrib/ltree/_ltree_gist.c,v 1.27 2010/02/24 18:02:24 tgl Exp $
  *
  *
  * GiST support for ltree[]
@@ -88,7 +88,7 @@ _ltree_compress(PG_FUNCTION_ARGS)
 		int			num = ArrayGetNItems(ARR_NDIM(val), ARR_DIMS(val));
 		ltree	   *item = (ltree *) ARR_DATA_PTR(val);
 
-		if (ARR_NDIM(val) != 1)
+		if (ARR_NDIM(val) > 1)
 			ereport(ERROR,
 					(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
 					 errmsg("array must be one-dimensional")));
@@ -534,7 +534,7 @@ _arrq_cons(ltree_gist *key, ArrayType *_query)
 	lquery	   *query = (lquery *) ARR_DATA_PTR(_query);
 	int			num = ArrayGetNItems(ARR_NDIM(_query), ARR_DIMS(_query));
 
-	if (ARR_NDIM(_query) != 1)
+	if (ARR_NDIM(_query) > 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
 				 errmsg("array must be one-dimensional")));

contrib/ltree/_ltree_op.c

 /*
- * $PostgreSQL: pgsql/contrib/ltree/_ltree_op.c,v 1.13 2009/06/11 14:48:51 momjian Exp $
+ * $PostgreSQL: pgsql/contrib/ltree/_ltree_op.c,v 1.14 2010/02/24 18:02:24 tgl Exp $
  *
  *
  * op function for ltree[]
@@ -48,7 +48,7 @@ array_iterator(ArrayType *la, PGCALL2 callback, void *param, ltree **found)
 	int			num = ArrayGetNItems(ARR_NDIM(la), ARR_DIMS(la));
 	ltree	   *item = (ltree *) ARR_DATA_PTR(la);
 
-	if (ARR_NDIM(la) != 1)
+	if (ARR_NDIM(la) > 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
 				 errmsg("array must be one-dimensional")));
@@ -148,7 +148,7 @@ _lt_q_regex(PG_FUNCTION_ARGS)
 	bool		res = false;
 	int			num = ArrayGetNItems(ARR_NDIM(_query), ARR_DIMS(_query));
 
-	if (ARR_NDIM(_query) != 1)
+	if (ARR_NDIM(_query) > 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
 				 errmsg("array must be one-dimensional")));
@@ -306,7 +306,7 @@ _lca(PG_FUNCTION_ARGS)
 	ltree	  **a,
 			   *res;
 
-	if (ARR_NDIM(la) != 1)
+	if (ARR_NDIM(la) > 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
 				 errmsg("array must be one-dimensional")));

contrib/ltree/lquery_op.c

 /*
  * op function for ltree and lquery
  * Teodor Sigaev <teodor@stack.net>
- * $PostgreSQL: pgsql/contrib/ltree/lquery_op.c,v 1.14 2009/06/11 14:48:51 momjian Exp $
+ * $PostgreSQL: pgsql/contrib/ltree/lquery_op.c,v 1.15 2010/02/24 18:02:24 tgl Exp $
  */
 #include "postgres.h"
 
@@ -344,7 +344,7 @@ lt_q_regex(PG_FUNCTION_ARGS)
 	bool		res = false;
 	int			num = ArrayGetNItems(ARR_NDIM(_query), ARR_DIMS(_query));
 
-	if (ARR_NDIM(_query) != 1)
+	if (ARR_NDIM(_query) > 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
 				 errmsg("array must be one-dimensional")));

contrib/ltree/ltree_gist.c

 /*
  * GiST support for ltree
  * Teodor Sigaev <teodor@stack.net>
- * $PostgreSQL: pgsql/contrib/ltree/ltree_gist.c,v 1.25 2009/06/11 14:48:51 momjian Exp $
+ * $PostgreSQL: pgsql/contrib/ltree/ltree_gist.c,v 1.26 2010/02/24 18:02:24 tgl Exp $
  */
 #include "postgres.h"
 
@@ -602,7 +602,7 @@ arrq_cons(ltree_gist *key, ArrayType *_query)
 	lquery	   *query = (lquery *) ARR_DATA_PTR(_query);
 	int			num = ArrayGetNItems(ARR_NDIM(_query), ARR_DIMS(_query));
 
-	if (ARR_NDIM(_query) != 1)
+	if (ARR_NDIM(_query) > 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
 				 errmsg("array must be one-dimensional")));