Support comma after last argument for function declarations (#3910)

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

tests/jerry/es.next/arrow-function.js

@@ -138,10 +138,8 @@ must_throw ("var x => x;");
 must_throw ("(()) => 0");
 must_throw ("((x)) => 0");
 must_throw ("(((x))) => 0");
-must_throw ("(x,) => 0");
 must_throw ("(x==6) => 0");
 must_throw ("(x y) => 0");
-must_throw ("(x,y,) => 0");
 must_throw ("x\n => 0");
 must_throw ("this => 0");
 must_throw ("(true) => 0");

tests/jerry/es.next/function-decl.js

@@ -0,0 +1,48 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+function check_syntax_error (code)
+{
+  try {
+    eval (code)
+    assert (false)
+  } catch (e) {
+    assert (e instanceof SyntaxError)
+  }
+}
+
+check_syntax_error ("function f(,) {}")
+check_syntax_error ("function f(...a,) {}")
+check_syntax_error ("function f(a = 1 + 1,,) {}")
+check_syntax_error ("function f(a,,b) {}")
+check_syntax_error ("function f(,a) {}")
+
+function f1(a,) {}
+assert(f1.length === 1)
+
+function f2(a = 1,) {}
+assert(f2.length === 1)
+
+function f3(a = 1, b = 1 + 1, c,) {}
+assert(f3.length === 3)
+
+var f4 = async(a,) => {}
+assert(f4.length === 1)
+
+var f5 = async(a = 1,) => {}
+assert(f5.length === 1)
+
+assert(((a = 1, b = 1 + 1, c,) => {}).length === 3)
+
+assert(((a = 1, b, c = 1 + 1,) => {}).length === 3)