Support sign function in parser (#740)

* support function sign in parser

* add test

Co-authored-by: Yee <2520865+yixinglu@users.noreply.github.com>

src/parser/parser.yy

@@ -893,6 +893,9 @@ function_call_expression
     | KW_TAGS L_PAREN opt_argument_list R_PAREN {
         $$ = new FunctionCallExpression(new std::string("tags"), $3);
     }
+    | KW_SIGN L_PAREN opt_argument_list R_PAREN {
+        $$ = new FunctionCallExpression(new std::string("sign"), $3);
+    }
     ;
 
 aggregate_expression

tests/tck/features/expression/FunctionCall.feature

+# Copyright (c) 2021 vesoft inc. All rights reserved.
+#
+# This source code is licensed under Apache 2.0 License,
+# attached with Common Clause Condition 1.0, found in the LICENSES directory.
+Feature: Function Call Expression
+
+  Background:
+    Given a graph with space named "nba"
+
+  Scenario: sign
+    When executing query:
+      """
+      YIELD sign(38) AS a, sign(-2) AS b, sign(0.421) AS c,
+            sign(-1.0) AS d, sign(0) AS e, sign(abs(-3)) AS f
+      """
+    Then the result should be, in any order:
+      | a | b  | c | d  | e | f |
+      | 1 | -1 | 1 | -1 | 0 | 1 |