Enhance CREATE FUNCTION parsing to support C functions with multiple arguments and flexible attribute order

Author: LucaCappelletti94

src/ast/ddl.rs

@@ -2768,7 +2768,15 @@ impl fmt::Display for CreateFunction {
             write!(f, " REMOTE WITH CONNECTION {remote_connection}")?;
         }
         if let Some(CreateFunctionBody::AsBeforeOptions(function_body)) = &self.function_body {
-            write!(f, " AS {function_body}")?;
+            write!(f, " AS ")?;
+            // Special handling for tuple expressions to format without parentheses
+            // PostgreSQL C functions use: AS 'obj_file', 'link_symbol'
+            // rather than: AS ('obj_file', 'link_symbol')
+            if let Expr::Tuple(exprs) = function_body {
+                write!(f, "{}", display_comma_separated(exprs))?;
+            } else {
+                write!(f, "{function_body}")?;
+            }
         }
         if let Some(CreateFunctionBody::Return(function_body)) = &self.function_body {
             write!(f, " RETURN {function_body}")?;

src/parser/mod.rs

@@ -10219,17 +10219,32 @@ impl<'a> Parser<'a> {
     /// Parse the body of a `CREATE FUNCTION` specified as a string.
     /// e.g. `CREATE FUNCTION ... AS $$ body $$`.
     fn parse_create_function_body_string(&mut self) -> Result<Expr, ParserError> {
-        let peek_token = self.peek_token();
-        let span = peek_token.span;
-        match peek_token.token {
-            Token::DollarQuotedString(s) if dialect_of!(self is PostgreSqlDialect | GenericDialect) =>
-            {
-                self.next_token();
-                Ok(Expr::Value(Value::DollarQuotedString(s).with_span(span)))
+        // Helper closure to parse a single string value (quoted or dollar-quoted)
+        let parse_string_expr = |parser: &mut Parser| -> Result<Expr, ParserError> {
+            let peek_token = parser.peek_token();
+            let span = peek_token.span;
+            match peek_token.token {
+                Token::DollarQuotedString(s) if dialect_of!(parser is PostgreSqlDialect | GenericDialect) =>
+                {
+                    parser.next_token();
+                    Ok(Expr::Value(Value::DollarQuotedString(s).with_span(span)))
+                }
+                _ => Ok(Expr::Value(
+                    Value::SingleQuotedString(parser.parse_literal_string()?).with_span(span),
+                )),
             }
-            _ => Ok(Expr::Value(
-                Value::SingleQuotedString(self.parse_literal_string()?).with_span(span),
-            )),
+        };
+
+        let first_expr = parse_string_expr(self)?;
+
+        // Check if there's a comma, indicating multiple strings (e.g., AS 'obj_file', 'link_symbol')
+        // This is used for C language functions: AS 'MODULE_PATHNAME', 'link_symbol'
+        if self.consume_token(&Token::Comma) {
+            let mut exprs = vec![first_expr];
+            exprs.extend(self.parse_comma_separated(parse_string_expr)?);
+            Ok(Expr::Tuple(exprs))
+        } else {
+            Ok(first_expr)
         }
     }
 

tests/sqlparser_postgres.rs

@@ -4482,6 +4482,50 @@ fn parse_incorrect_create_function_parallel() {
     assert!(pg().parse_sql_statements(sql).is_err());
 }
 
+#[test]
+fn parse_create_function_c_with_module_pathname() {
+    let sql = "CREATE FUNCTION cas_in(input cstring) RETURNS cas LANGUAGE c IMMUTABLE PARALLEL SAFE AS 'MODULE_PATHNAME', 'cas_in_wrapper'";
+    assert_eq!(
+        pg_and_generic().verified_stmt(sql),
+        Statement::CreateFunction(CreateFunction {
+            or_alter: false,
+            or_replace: false,
+            temporary: false,
+            name: ObjectName::from(vec![Ident::new("cas_in")]),
+            args: Some(vec![OperateFunctionArg::with_name(
+                "input",
+                DataType::Custom(ObjectName::from(vec![Ident::new("cstring")]), vec![]),
+            ),]),
+            return_type: Some(DataType::Custom(
+                ObjectName::from(vec![Ident::new("cas")]),
+                vec![]
+            )),
+            language: Some("c".into()),
+            behavior: Some(FunctionBehavior::Immutable),
+            called_on_null: None,
+            parallel: Some(FunctionParallel::Safe),
+            function_body: Some(CreateFunctionBody::AsBeforeOptions(Expr::Tuple(vec![
+                Expr::Value(
+                    (Value::SingleQuotedString("MODULE_PATHNAME".into())).with_empty_span()
+                ),
+                Expr::Value((Value::SingleQuotedString("cas_in_wrapper".into())).with_empty_span()),
+            ]))),
+            if_not_exists: false,
+            using: None,
+            determinism_specifier: None,
+            options: None,
+            remote_connection: None,
+        })
+    );
+
+    // Test that attribute order flexibility works (IMMUTABLE before LANGUAGE)
+    let sql_alt_order = "CREATE FUNCTION cas_in(input cstring) RETURNS cas IMMUTABLE PARALLEL SAFE LANGUAGE c AS 'MODULE_PATHNAME', 'cas_in_wrapper'";
+    pg_and_generic().one_statement_parses_to(
+        sql_alt_order,
+        "CREATE FUNCTION cas_in(input cstring) RETURNS cas LANGUAGE c IMMUTABLE PARALLEL SAFE AS 'MODULE_PATHNAME', 'cas_in_wrapper'"
+    );
+}
+
 #[test]
 fn parse_drop_function() {
     let sql = "DROP FUNCTION IF EXISTS test_func";