Refactor: replace some dialect_of! checks with Dialect trait methods (apache#2171)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: andygrove

src/dialect/databricks.rs

@@ -79,4 +79,9 @@ impl Dialect for DatabricksDialect {
     fn supports_group_by_with_modifier(&self) -> bool {
         true
     }
+
+    /// See <https://docs.databricks.com/en/sql/language-manual/sql-ref-syntax-qry-select-values.html>
+    fn supports_values_as_table_factor(&self) -> bool {
+        true
+    }
 }

src/dialect/generic.rs

@@ -104,6 +104,22 @@ impl Dialect for GenericDialect {
         true
     }
 
+    fn supports_extract_comma_syntax(&self) -> bool {
+        true
+    }
+
+    fn supports_create_view_comment_syntax(&self) -> bool {
+        true
+    }
+
+    fn supports_parens_around_table_factor(&self) -> bool {
+        true
+    }
+
+    fn supports_values_as_table_factor(&self) -> bool {
+        true
+    }
+
     fn supports_create_index_with_clause(&self) -> bool {
         true
     }

src/dialect/mod.rs

@@ -856,6 +856,87 @@ pub trait Dialect: Debug + Any {
         false
     }
 
+    /// Returns true if this dialect supports the `EXTRACT` function
+    /// with a comma separator instead of `FROM`.
+    ///
+    /// Example:
+    /// ```sql
+    /// SELECT EXTRACT(YEAR, date_column) FROM table;
+    /// ```
+    ///
+    /// [Snowflake](https://docs.snowflake.com/en/sql-reference/functions/extract)
+    fn supports_extract_comma_syntax(&self) -> bool {
+        false
+    }
+
+    /// Returns true if this dialect supports a subquery passed to a function
+    /// as the only argument without enclosing parentheses.
+    ///
+    /// Example:
+    /// ```sql
+    /// SELECT FLATTEN(SELECT * FROM tbl);
+    /// ```
+    ///
+    /// [Snowflake](https://docs.snowflake.com/en/sql-reference/functions/flatten)
+    fn supports_subquery_as_function_arg(&self) -> bool {
+        false
+    }
+
+    /// Returns true if this dialect supports the `COMMENT` clause in
+    /// `CREATE VIEW` statements using the `COMMENT = 'comment'` syntax.
+    ///
+    /// Example:
+    /// ```sql
+    /// CREATE VIEW v COMMENT = 'my comment' AS SELECT 1;
+    /// ```
+    ///
+    /// [Snowflake](https://docs.snowflake.com/en/sql-reference/sql/create-view#optional-parameters)
+    fn supports_create_view_comment_syntax(&self) -> bool {
+        false
+    }
+
+    /// Returns true if this dialect supports the `ARRAY` type without
+    /// specifying an element type.
+    ///
+    /// Example:
+    /// ```sql
+    /// CREATE TABLE t (a ARRAY);
+    /// ```
+    ///
+    /// [Snowflake](https://docs.snowflake.com/en/sql-reference/data-types-semistructured#array)
+    fn supports_array_typedef_without_element_type(&self) -> bool {
+        false
+    }
+
+    /// Returns true if this dialect supports extra parentheses around
+    /// lone table names or derived tables in the `FROM` clause.
+    ///
+    /// Example:
+    /// ```sql
+    /// SELECT * FROM (mytable);
+    /// SELECT * FROM ((SELECT 1));
+    /// SELECT * FROM (mytable) AS alias;
+    /// ```
+    ///
+    /// [Snowflake](https://docs.snowflake.com/en/sql-reference/constructs/from)
+    fn supports_parens_around_table_factor(&self) -> bool {
+        false
+    }
+
+    /// Returns true if this dialect supports `VALUES` as a table factor
+    /// without requiring parentheses around the entire clause.
+    ///
+    /// Example:
+    /// ```sql
+    /// SELECT * FROM VALUES (1, 'a'), (2, 'b') AS t (col1, col2);
+    /// ```
+    ///
+    /// [Snowflake](https://docs.snowflake.com/en/sql-reference/constructs/values)
+    /// [Databricks](https://docs.databricks.com/en/sql/language-manual/sql-ref-syntax-qry-select-values.html)
+    fn supports_values_as_table_factor(&self) -> bool {
+        false
+    }
+
     /// Returns true if this dialect allows dollar placeholders
     /// e.g. `SELECT $var` (SQLite)
     fn supports_dollar_placeholder(&self) -> bool {

src/dialect/snowflake.rs

@@ -211,6 +211,36 @@ impl Dialect for SnowflakeDialect {
         true
     }
 
+    /// See [doc](https://docs.snowflake.com/en/sql-reference/functions/extract)
+    fn supports_extract_comma_syntax(&self) -> bool {
+        true
+    }
+
+    /// See [doc](https://docs.snowflake.com/en/sql-reference/functions/flatten)
+    fn supports_subquery_as_function_arg(&self) -> bool {
+        true
+    }
+
+    /// See [doc](https://docs.snowflake.com/en/sql-reference/sql/create-view#optional-parameters)
+    fn supports_create_view_comment_syntax(&self) -> bool {
+        true
+    }
+
+    /// See [doc](https://docs.snowflake.com/en/sql-reference/data-types-semistructured#array)
+    fn supports_array_typedef_without_element_type(&self) -> bool {
+        true
+    }
+
+    /// See [doc](https://docs.snowflake.com/en/sql-reference/constructs/from)
+    fn supports_parens_around_table_factor(&self) -> bool {
+        true
+    }
+
+    /// See [doc](https://docs.snowflake.com/en/sql-reference/constructs/values)
+    fn supports_values_as_table_factor(&self) -> bool {
+        true
+    }
+
     fn parse_statement(&self, parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
         if parser.parse_keyword(Keyword::BEGIN) {
             return Some(parser.parse_begin_exception_end());

src/parser/mod.rs

@@ -2293,7 +2293,7 @@ impl<'a> Parser<'a> {
 
         // Snowflake permits a subquery to be passed as an argument without
         // an enclosing set of parens if it's the only argument.
-        if dialect_of!(self is SnowflakeDialect) && self.peek_sub_query() {
+        if self.dialect.supports_subquery_as_function_arg() && self.peek_sub_query() {
             let subquery = self.parse_query()?;
             self.expect_token(&Token::RParen)?;
             return Ok(Function {
@@ -2683,8 +2683,7 @@ impl<'a> Parser<'a> {
 
         let syntax = if self.parse_keyword(Keyword::FROM) {
             ExtractSyntax::From
-        } else if self.consume_token(&Token::Comma)
-            && dialect_of!(self is SnowflakeDialect | GenericDialect)
+        } else if self.dialect.supports_extract_comma_syntax() && self.consume_token(&Token::Comma)
         {
             ExtractSyntax::Comma
         } else {
@@ -6228,7 +6227,7 @@ impl<'a> Parser<'a> {
             None
         };
 
-        let comment = if dialect_of!(self is SnowflakeDialect | GenericDialect)
+        let comment = if self.dialect.supports_create_view_comment_syntax()
             && self.parse_keyword(Keyword::COMMENT)
         {
             self.expect_token(&Token::Eq)?;
@@ -11790,7 +11789,7 @@ impl<'a> Parser<'a> {
                 Keyword::ENUM16 => Ok(DataType::Enum(self.parse_enum_values()?, Some(16))),
                 Keyword::SET => Ok(DataType::Set(self.parse_string_values()?)),
                 Keyword::ARRAY => {
-                    if dialect_of!(self is SnowflakeDialect) {
+                    if self.dialect.supports_array_typedef_without_element_type() {
                         Ok(DataType::Array(ArrayElemTypeDef::None))
                     } else if dialect_of!(self is ClickHouseDialect) {
                         Ok(self.parse_sub_type(|internal_type| {
@@ -14989,7 +14988,7 @@ impl<'a> Parser<'a> {
                     table_with_joins: Box::new(table_and_joins),
                     alias,
                 })
-            } else if dialect_of!(self is SnowflakeDialect | GenericDialect) {
+            } else if self.dialect.supports_parens_around_table_factor() {
                 // Dialect-specific behavior: Snowflake diverges from the
                 // standard and from most of the other implementations by
                 // allowing extra parentheses not only around a join (B), but
@@ -15035,7 +15034,7 @@ impl<'a> Parser<'a> {
                 // appearing alone in parentheses (e.g. `FROM (mytable)`)
                 self.expected("joined table", self.peek_token())
             }
-        } else if dialect_of!(self is SnowflakeDialect | DatabricksDialect | GenericDialect)
+        } else if self.dialect.supports_values_as_table_factor()
             && matches!(
                 self.peek_tokens(),
                 [