Fix CREATE FUNCTION round trip for Hive dialect (apache#1693)

Author: iffyio

src/ast/ddl.rs

@@ -2011,8 +2011,6 @@ impl fmt::Display for CreateFunction {
         )?;
         if let Some(args) = &self.args {
             write!(f, "({})", display_comma_separated(args))?;
-        } else {
-            write!(f, "()")?;
         }
         if let Some(return_type) = &self.return_type {
             write!(f, " RETURNS {return_type}")?;

src/parser/mod.rs

@@ -4563,14 +4563,13 @@ impl<'a> Parser<'a> {
         temporary: bool,
     ) -> Result<Statement, ParserError> {
         let name = self.parse_object_name(false)?;
+
         self.expect_token(&Token::LParen)?;
-        let args = if self.consume_token(&Token::RParen) {
-            self.prev_token();
-            None
+        let args = if Token::RParen != self.peek_token_ref().token {
+            self.parse_comma_separated(Parser::parse_function_arg)?
         } else {
-            Some(self.parse_comma_separated(Parser::parse_function_arg)?)
+            vec![]
         };
-
         self.expect_token(&Token::RParen)?;
 
         let return_type = if self.parse_keyword(Keyword::RETURNS) {
@@ -4666,7 +4665,7 @@ impl<'a> Parser<'a> {
             or_replace,
             temporary,
             name,
-            args,
+            args: Some(args),
             return_type,
             behavior: body.behavior,
             called_on_null: body.called_on_null,

tests/sqlparser_postgres.rs

@@ -5147,7 +5147,7 @@ fn parse_trigger_related_functions() {
             temporary: false,
             if_not_exists: false,
             name: ObjectName::from(vec![Ident::new("emp_stamp")]),
-            args: None,
+            args: Some(vec![]),
             return_type: Some(DataType::Trigger),
             function_body: Some(
                 CreateFunctionBody::AsBeforeOptions(