Enhancing Trailing Comma Option (#1212)

src/dialect/bigquery.rs

@@ -22,6 +22,10 @@ impl Dialect for BigQueryDialect {
         ch == '`'
     }
 
+    fn supports_projection_trailing_commas(&self) -> bool {
+        true
+    }
+
     fn is_identifier_start(&self, ch: char) -> bool {
         ch.is_ascii_lowercase() || ch.is_ascii_uppercase() || ch == '_'
     }

src/dialect/duckdb.rs

@@ -18,6 +18,10 @@ pub struct DuckDbDialect;
 
 // In most cases the redshift dialect is identical to [`PostgresSqlDialect`].
 impl Dialect for DuckDbDialect {
+    fn supports_trailing_commas(&self) -> bool {
+        true
+    }
+
     fn is_identifier_start(&self, ch: char) -> bool {
         ch.is_alphabetic() || ch == '_'
     }

src/dialect/mod.rs

@@ -251,6 +251,14 @@ pub trait Dialect: Debug + Any {
         // return None to fall back to the default behavior
         None
     }
+    /// Does the dialect support trailing commas around the query?
+    fn supports_trailing_commas(&self) -> bool {
+        false
+    }
+    /// Does the dialect support trailing commas in the projection list?
+    fn supports_projection_trailing_commas(&self) -> bool {
+        self.supports_trailing_commas()
+    }
     /// Dialect-specific infix parser override
     fn parse_infix(
         &self,

src/dialect/snowflake.rs

@@ -38,6 +38,10 @@ impl Dialect for SnowflakeDialect {
         ch.is_ascii_lowercase() || ch.is_ascii_uppercase() || ch == '_'
     }
 
+    fn supports_projection_trailing_commas(&self) -> bool {
+        true
+    }
+
     fn is_identifier_part(&self, ch: char) -> bool {
         ch.is_ascii_lowercase()
             || ch.is_ascii_uppercase()

src/parser/mod.rs

@@ -305,7 +305,7 @@ impl<'a> Parser<'a> {
             state: ParserState::Normal,
             dialect,
             recursion_counter: RecursionCounter::new(DEFAULT_REMAINING_DEPTH),
-            options: ParserOptions::default(),
+            options: ParserOptions::new().with_trailing_commas(dialect.supports_trailing_commas()),
         }
     }
 
@@ -3225,7 +3225,7 @@ impl<'a> Parser<'a> {
         // This pattern could be captured better with RAII type semantics, but it's quite a bit of
         // code to add for just one case, so we'll just do it manually here.
         let old_value = self.options.trailing_commas;
-        self.options.trailing_commas |= dialect_of!(self is BigQueryDialect | SnowflakeDialect);
+        self.options.trailing_commas |= self.dialect.supports_projection_trailing_commas();
 
         let ret = self.parse_comma_separated(|p| p.parse_select_item());
         self.options.trailing_commas = old_value;
@@ -5413,12 +5413,17 @@ impl<'a> Parser<'a> {
             } else {
                 return self.expected("column name or constraint definition", self.peek_token());
             }
+
             let comma = self.consume_token(&Token::Comma);
-            if self.consume_token(&Token::RParen) {
-                // allow a trailing comma, even though it's not in standard
-                break;
-            } else if !comma {
+            let rparen = self.peek_token().token == Token::RParen;
+
+            if !comma && !rparen {
                 return self.expected("',' or ')' after column definition", self.peek_token());
+            };
+
+            if rparen && (!comma || self.options.trailing_commas) {
+                let _ = self.consume_token(&Token::RParen);
+                break;
             }
         }
 
@@ -9411,6 +9416,9 @@ impl<'a> Parser<'a> {
                 with_privileges_keyword: self.parse_keyword(Keyword::PRIVILEGES),
             }
         } else {
+            let old_value = self.options.trailing_commas;
+            self.options.trailing_commas = false;
+
             let (actions, err): (Vec<_>, Vec<_>) = self
                 .parse_comma_separated(Parser::parse_grant_permission)?
                 .into_iter()
@@ -9434,6 +9442,8 @@ impl<'a> Parser<'a> {
                 })
                 .partition(Result::is_ok);
 
+            self.options.trailing_commas = old_value;
+
             if !err.is_empty() {
                 let errors: Vec<Keyword> = err.into_iter().filter_map(|x| x.err()).collect();
                 return Err(ParserError::ParserError(format!(
@@ -9939,6 +9949,12 @@ impl<'a> Parser<'a> {
             Expr::Wildcard => Ok(SelectItem::Wildcard(
                 self.parse_wildcard_additional_options()?,
             )),
+            Expr::Identifier(v) if v.value.to_lowercase() == "from" => {
+                parser_err!(
+                    format!("Expected an expression, found: {}", v),
+                    self.peek_token().location
+                )
+            }
             expr => self
                 .parse_optional_alias(keywords::RESERVED_FOR_COLUMN_ALIAS)
                 .map(|alias| match alias {

tests/sqlparser_common.rs

@@ -3552,8 +3552,13 @@ fn parse_create_table_clone() {
 
 #[test]
 fn parse_create_table_trailing_comma() {
-    let sql = "CREATE TABLE foo (bar int,)";
-    all_dialects().one_statement_parses_to(sql, "CREATE TABLE foo (bar INT)");
+    let dialect = TestedDialects {
+        dialects: vec![Box::new(DuckDbDialect {})],
+        options: None,
+    };
+
+    let sql = "CREATE TABLE foo (bar int,);";
+    dialect.one_statement_parses_to(sql, "CREATE TABLE foo (bar INT)");
 }
 
 #[test]
@@ -4418,7 +4423,7 @@ fn parse_window_clause() {
     ORDER BY C3";
     verified_only_select(sql);
 
-    let sql = "SELECT from mytable WINDOW window1 AS window2";
+    let sql = "SELECT * from mytable WINDOW window1 AS window2";
     let dialects = all_dialects_except(|d| d.is::<BigQueryDialect>() || d.is::<GenericDialect>());
     let res = dialects.parse_sql_statements(sql);
     assert_eq!(
@@ -8846,9 +8851,11 @@ fn parse_non_latin_identifiers() {
 
 #[test]
 fn parse_trailing_comma() {
+    // At the moment, Duck DB is the only dialect that allows
+    // trailing commas anywhere in the query
     let trailing_commas = TestedDialects {
-        dialects: vec![Box::new(GenericDialect {})],
-        options: Some(ParserOptions::new().with_trailing_commas(true)),
+        dialects: vec![Box::new(DuckDbDialect {})],
+        options: None,
     };
 
     trailing_commas.one_statement_parses_to(
@@ -8866,11 +8873,74 @@ fn parse_trailing_comma() {
         "SELECT DISTINCT ON (album_id) name FROM track",
     );
 
+    trailing_commas.one_statement_parses_to(
+        "CREATE TABLE employees (name text, age int,)",
+        "CREATE TABLE employees (name TEXT, age INT)",
+    );
+
     trailing_commas.verified_stmt("SELECT album_id, name FROM track");
 
     trailing_commas.verified_stmt("SELECT * FROM track ORDER BY milliseconds");
 
     trailing_commas.verified_stmt("SELECT DISTINCT ON (album_id) name FROM track");
+
+    // doesn't allow any trailing commas
+    let trailing_commas = TestedDialects {
+        dialects: vec![Box::new(GenericDialect {})],
+        options: None,
+    };
+
+    assert_eq!(
+        trailing_commas
+            .parse_sql_statements("SELECT name, age, from employees;")
+            .unwrap_err(),
+        ParserError::ParserError("Expected an expression, found: from".to_string())
+    );
+
+    assert_eq!(
+        trailing_commas
+            .parse_sql_statements("CREATE TABLE employees (name text, age int,)")
+            .unwrap_err(),
+        ParserError::ParserError(
+            "Expected column name or constraint definition, found: )".to_string()
+        )
+    );
+}
+
+#[test]
+fn parse_projection_trailing_comma() {
+    // Some dialects allow trailing commas only in the projection
+    let trailing_commas = TestedDialects {
+        dialects: vec![Box::new(SnowflakeDialect {}), Box::new(BigQueryDialect {})],
+        options: None,
+    };
+
+    trailing_commas.one_statement_parses_to(
+        "SELECT album_id, name, FROM track",
+        "SELECT album_id, name FROM track",
+    );
+
+    trailing_commas.verified_stmt("SELECT album_id, name FROM track");
+
+    trailing_commas.verified_stmt("SELECT * FROM track ORDER BY milliseconds");
+
+    trailing_commas.verified_stmt("SELECT DISTINCT ON (album_id) name FROM track");
+
+    assert_eq!(
+        trailing_commas
+            .parse_sql_statements("SELECT * FROM track ORDER BY milliseconds,")
+            .unwrap_err(),
+        ParserError::ParserError("Expected an expression:, found: EOF".to_string())
+    );
+
+    assert_eq!(
+        trailing_commas
+            .parse_sql_statements("CREATE TABLE employees (name text, age int,)")
+            .unwrap_err(),
+        ParserError::ParserError(
+            "Expected column name or constraint definition, found: )".to_string()
+        ),
+    );
 }
 
 #[test]

tests/sqlparser_postgres.rs

@@ -3701,7 +3701,7 @@ fn parse_create_table_with_alias() {
       int2_col INT2,
       float8_col FLOAT8,
       float4_col FLOAT4,
-      bool_col BOOL,
+      bool_col BOOL
     );";
     match pg_and_generic().one_statement_parses_to(sql, "") {
         Statement::CreateTable(CreateTable {