feat: support trailing comma after the last argument (robertkrimen#520)

Add support for trailing comma after the last argument of a method call.

parser/expression.go

@@ -384,21 +384,19 @@ func (p *parser) parseArgumentList() (argumentList []ast.Expression, idx0, idx1
  p.comments.Unset()
  }
  idx0 = p.expect(token.LEFT_PARENTHESIS)
- if p.token != token.RIGHT_PARENTHESIS {
- for {
- exp := p.parseAssignmentExpression()
- if p.mode&StoreComments != 0 {
- p.comments.SetExpression(exp)
- }
- argumentList = append(argumentList, exp)
- if p.token != token.COMMA {
- break
- }
- if p.mode&StoreComments != 0 {
- p.comments.Unset()
- }
- p.next()
+ for p.token != token.RIGHT_PARENTHESIS {
+ exp := p.parseAssignmentExpression()
+ if p.mode&StoreComments != 0 {
+ p.comments.SetExpression(exp)
+ }
+ argumentList = append(argumentList, exp)
+ if p.token != token.COMMA {
+ break
  }
+ if p.mode&StoreComments != 0 {
+ p.comments.Unset()
+ }
+ p.next()
  }
  if p.mode&StoreComments != 0 {
  p.comments.Unset()

parser/parser_test.go

@@ -879,6 +879,15 @@ func TestParser(t *testing.T) {
  2
  debugger
  `, nil)
+
+ test(`
+ function mergeObjects(x, y) { /* dummy body */}
+
+ mergeObjects(
+ { "duck": "quack" },
+ { "dog": "bark" }, // Allow trailing comma after the last argument.
+ );
+ `, nil)
  })
 }