Add tab completion for EXPLAIN (SETTINGS) in psql

Author: Justin Pryzby
Reviewed-by: Tatsuro Yamada
Discussion: https://postgr.es/m/20190927022051.GC24334@telsasoft.com
Backpatch-through: 12

Author: michaelpq

src/bin/psql/tab-complete.c

@@ -2939,9 +2939,9 @@ psql_completion(const char *text, int start, int end)
 		 * one word, so the above test is correct.
 		 */
 		if (ends_with(prev_wd, '(') || ends_with(prev_wd, ','))
-			COMPLETE_WITH("ANALYZE", "VERBOSE", "COSTS", "BUFFERS",
-						  "TIMING", "SUMMARY", "FORMAT");
-		else if (TailMatches("ANALYZE|VERBOSE|COSTS|BUFFERS|TIMING|SUMMARY"))
+			COMPLETE_WITH("ANALYZE", "VERBOSE", "COSTS", "SETTINGS",
+						  "BUFFERS", "TIMING", "SUMMARY", "FORMAT");
+		else if (TailMatches("ANALYZE|VERBOSE|COSTS|SETTINGS|BUFFERS|TIMING|SUMMARY"))
 			COMPLETE_WITH("ON", "OFF");
 		else if (TailMatches("FORMAT"))
 			COMPLETE_WITH("TEXT", "XML", "JSON", "YAML");