Bug in comparison of empty jsonb arrays to scalars

diff --git a/src/backend/utils/adt/jsonb_util.c b/src/backend/utils/adt/jsonb_util.c
index ddc34ce..43934bf 100644
--- a/src/backend/utils/adt/jsonb_util.c
+++ b/src/backend/utils/adt/jsonb_util.c
@@ -232,7 +232,7 @@ compareJsonbContainers(JsonbContainer *a, JsonbContainer *b)
 						 */
 						if (va.val.array.rawScalar != vb.val.array.rawScalar)
 							res = (va.val.array.rawScalar) ? -1 : 1;
-						if (va.val.array.nElems != vb.val.array.nElems)
+						else if (va.val.array.nElems != vb.val.array.nElems)
 							res = (va.val.array.nElems > vb.val.array.nElems) ? 1 : -1;
 						break;
 					case jbvObject:
diff --git a/src/bin/pg_upgrade/check.c b/src/bin/pg_upgrade/check.c
index 42bf499..81c1616 100644
--- a/src/bin/pg_upgrade/check.c
+++ b/src/bin/pg_upgrade/check.c
@@ -115,6 +115,11 @@ check_and_dump_old_cluster(bool live_check)
 	if (GET_MAJOR_VERSION(old_cluster.major_version) <= 804)
 		new_9_0_populate_pg_largeobject_metadata(&old_cluster, true);
 
+	/* Pre-PG 10.0 had bug in jsonb comparison operator  */
+	if (GET_MAJOR_VERSION(old_cluster.major_version) <= 906 &&
+		GET_MAJOR_VERSION(old_cluster.major_version) >= 904)
+		old_9_6_invalidate_jsonb_btree_indexes(&old_cluster, true);
+
 	/*
 	 * While not a check option, we do this now because this is the only time
 	 * the old server is running.
@@ -166,11 +171,26 @@ report_clusters_compatible(void)
 void
 issue_warnings(void)
 {
-	/* Create dummy large object permissions for old < PG 9.0? */
-	if (GET_MAJOR_VERSION(old_cluster.major_version) <= 804)
+	bool need_new_9_0_populate_pg_largeobject_metadata =
+			GET_MAJOR_VERSION(old_cluster.major_version) <= 804;
+
+	bool need_old_9_6_invalidate_jsonb_btree_indexes =
+			GET_MAJOR_VERSION(old_cluster.major_version) <= 906 &&
+			GET_MAJOR_VERSION(old_cluster.major_version) >= 904;
+
+	if (need_new_9_0_populate_pg_largeobject_metadata ||
+		need_old_9_6_invalidate_jsonb_btree_indexes)
 	{
 		start_postmaster(&new_cluster, true);
-		new_9_0_populate_pg_largeobject_metadata(&new_cluster, false);
+
+		/* Create dummy large object permissions for old < PG 9.0? */
+		if (need_new_9_0_populate_pg_largeobject_metadata)
+			new_9_0_populate_pg_largeobject_metadata(&new_cluster, false);
+
+		/* invalidate jsonb btree indexes for old < PG 10.0  */
+		if (need_old_9_6_invalidate_jsonb_btree_indexes)
+			old_9_6_invalidate_jsonb_btree_indexes(&new_cluster, false);
+
 		stop_postmaster(false);
 	}
 }
diff --git a/src/bin/pg_upgrade/pg_upgrade.h b/src/bin/pg_upgrade/pg_upgrade.h
index 19dca83..07e0ca6 100644
--- a/src/bin/pg_upgrade/pg_upgrade.h
+++ b/src/bin/pg_upgrade/pg_upgrade.h
@@ -442,6 +442,8 @@ void		pg_putenv(const char *var, const char *val);
 void new_9_0_populate_pg_largeobject_metadata(ClusterInfo *cluster,
 										 bool check_mode);
 void		old_9_3_check_for_line_data_type_usage(ClusterInfo *cluster);
+void old_9_6_invalidate_jsonb_btree_indexes(ClusterInfo *cluster,
+											bool check_mode);
 
 /* parallel.c */
 void parallel_exec_prog(const char *log_file, const char *opt_log_file,
diff --git a/src/bin/pg_upgrade/version.c b/src/bin/pg_upgrade/version.c
index 3c7c5fa..b1a3b89 100644
--- a/src/bin/pg_upgrade/version.c
+++ b/src/bin/pg_upgrade/version.c
@@ -10,6 +10,7 @@
 #include "postgres_fe.h"
 
 #include "pg_upgrade.h"
+#include "catalog/pg_type.h"
 #include "fe_utils/string_utils.h"
 
 
@@ -185,3 +186,116 @@ old_9_3_check_for_line_data_type_usage(ClusterInfo *cluster)
 	else
 		check_ok();
 }
+
+/*
+ * old_9_6_invalidate_jsonb_btree_indexes()
+ *	9.4-9.6 -> 10.0
+ *	Btree index ordering for jsonb had been fixed in 10.0
+ */
+void
+old_9_6_invalidate_jsonb_btree_indexes(ClusterInfo *cluster, bool check_mode)
+{
+	int			dbnum;
+	FILE	   *script = NULL;
+	bool		found = false;
+	char		output_path[MAXPGPATH];
+
+	prep_status("Checking for jsonb btree indexes existence");
+
+	snprintf(output_path, sizeof(output_path), "reindex_jsonb_btree.sql");
+
+	for (dbnum = 0; dbnum < cluster->dbarr.ndbs; dbnum++)
+	{
+		PGresult   *res;
+		bool		db_used = false;
+		int			ntups;
+		int			rowno;
+		int			i_nspname,
+					i_relname;
+		DbInfo	   *active_db = &cluster->dbarr.dbs[dbnum];
+		PGconn	   *conn = connectToServer(cluster, active_db->db_name);
+
+		/* find jsonb btree indexes */
+		res = executeQueryOrDie(conn,
+								"SELECT DISTINCT n.nspname, c.relname "
+								"FROM	pg_catalog.pg_class c, "
+								"		pg_catalog.pg_index i, "
+								"		pg_catalog.pg_am am, "
+								"		pg_catalog.pg_namespace n, "
+								"		pg_catalog.pg_attribute a "
+								"WHERE	i.indexrelid = c.oid AND "
+								"		c.relam = am.oid AND "
+								"		c.relnamespace = n.oid AND "
+								"		a.attrelid = c.oid AND "
+								"		a.atttypid = " CppAsString2(JSONBOID) " AND "
+								"		am.amname = 'btree'");
+
+		ntups = PQntuples(res);
+		i_nspname = PQfnumber(res, "nspname");
+		i_relname = PQfnumber(res, "relname");
+
+		for (rowno = 0; rowno < ntups; rowno++)
+		{
+			found = true;
+			if (!check_mode)
+			{
+				if (script == NULL && (script = fopen_priv(output_path, "w")) == NULL)
+					pg_fatal("could not open file \"%s\": %s\n", output_path, strerror(errno));
+				if (!db_used)
+				{
+					fprintf(script, "\\connect %s\n",
+							quote_identifier(active_db->db_name));
+					db_used = true;
+				}
+				fprintf(script, "REINDEX INDEX %s.%s;\n",
+						quote_identifier(PQgetvalue(res, rowno, i_nspname)),
+						quote_identifier(PQgetvalue(res, rowno, i_relname)));
+			}
+		}
+
+		PQclear(res);
+
+		if (!check_mode && found)
+			/* mark jsonb btree indexes as invalid */
+			PQclear(executeQueryOrDie(conn,
+									  "UPDATE pg_catalog.pg_index i "
+									  "SET	indisvalid = false "
+									  "FROM	pg_catalog.pg_class c, "
+									  "		pg_catalog.pg_am am, "
+									  "		pg_catalog.pg_namespace n, "
+									  "		pg_catalog.pg_attribute a "
+									  "WHERE	i.indexrelid = c.oid AND "
+									  "		c.relam = am.oid AND "
+									  "		c.relnamespace = n.oid AND "
+									  "		a.attrelid = c.oid AND "
+									  "		a.atttypid = " CppAsString2(JSONBOID) " AND "
+									  "		am.amname = 'btree'"));
+
+		PQfinish(conn);
+	}
+
+	if (script)
+		fclose(script);
+
+	if (found)
+	{
+		report_status(PG_WARNING, "warning");
+		if (check_mode)
+			pg_log(PG_WARNING, "\n"
+				   "Your installation contains jsonb btree indexes.  These indexes have\n"
+				   "different comparison rules between your old and new clusters, so they\n"
+				   "must be reindexed with the REINDEX command.  After upgrading, you will\n"
+				   "be given REINDEX instructions.\n\n");
+		else
+			pg_log(PG_WARNING, "\n"
+				   "Your installation contains jsonb btree indexes.  These indexes have\n"
+				   "different comparison rules between your old and new clusters, so they\n"
+				   "must be reindexed with the REINDEX command.  The file:\n"
+				   "    %s\n"
+				   "when executed by psql by the database superuser will recreate all invalid\n"
+				   "indexes; until then, none of these indexes will be used.\n\n",
+				   output_path);
+	}
+	else
+		check_ok();
+}
diff --git a/src/test/regress/expected/jsonb.out b/src/test/regress/expected/jsonb.out
index e2cb08a..203088d 100644
--- a/src/test/regress/expected/jsonb.out
+++ b/src/test/regress/expected/jsonb.out
@@ -2256,6 +2256,13 @@ SELECT count(*) FROM testjsonb WHERE j = '{"pos":98, "line":371, "node":"CBA", "
      1
 (1 row)
 
+-- bug in comparison of [] and scalars
+SELECT '[]'::jsonb > 'null'::jsonb;
+ ?column? 
+----------
+ t
+(1 row)
+
 --gin path opclass
 DROP INDEX jidx;
 CREATE INDEX jidx ON testjsonb USING gin (j jsonb_path_ops);
diff --git a/src/test/regress/sql/jsonb.sql b/src/test/regress/sql/jsonb.sql
index 6b4c796..2d37c4f 100644
--- a/src/test/regress/sql/jsonb.sql
+++ b/src/test/regress/sql/jsonb.sql
@@ -580,6 +580,9 @@ SET enable_seqscan = off;
 SELECT count(*) FROM testjsonb WHERE j > '{"p":1}';
 SELECT count(*) FROM testjsonb WHERE j = '{"pos":98, "line":371, "node":"CBA", "indexed":true}';
 
+-- bug in comparison of [] and scalars
+SELECT '[]'::jsonb > 'null'::jsonb;
+
 --gin path opclass
 DROP INDEX jidx;
 CREATE INDEX jidx ON testjsonb USING gin (j jsonb_path_ops);