Use separate trait impl in favor of dialect_of! macro

Author: bombsimon

src/dialect/bigquery.rs

@@ -15,9 +15,10 @@
 // specific language governing permissions and limitations
 // under the License.
 
+use crate::ast::Statement;
 use crate::dialect::Dialect;
 use crate::keywords::Keyword;
-use crate::parser::Parser;
+use crate::parser::{Parser, ParserError};
 
 /// These keywords are disallowed as column identifiers. Such that
 /// `SELECT 5 AS <col> FROM T` is rejected by BigQuery.
@@ -44,6 +45,14 @@ const RESERVED_FOR_COLUMN_ALIAS: &[Keyword] = &[
 pub struct BigQueryDialect;
 
 impl Dialect for BigQueryDialect {
+    fn parse_statement(&self, parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
+        if parser.parse_keyword(Keyword::BEGIN) {
+            return Some(parser.parse_begin_exception_end());
+        }
+
+        None
+    }
+
     /// See <https://cloud.google.com/bigquery/docs/reference/standard-sql/lexical#identifiers>
     fn is_delimited_identifier_start(&self, ch: char) -> bool {
         ch == '`'

src/dialect/snowflake.rs

@@ -131,6 +131,10 @@ impl Dialect for SnowflakeDialect {
     }
 
     fn parse_statement(&self, parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
+        if parser.parse_keyword(Keyword::BEGIN) {
+            return Some(parser.parse_begin_exception_end());
+        }
+
         if parser.parse_keywords(&[Keyword::ALTER, Keyword::SESSION]) {
             // ALTER SESSION
             let set = match parser.parse_one_of_keywords(&[Keyword::SET, Keyword::UNSET]) {

src/parser/mod.rs

@@ -15102,10 +15102,6 @@ impl<'a> Parser<'a> {
     }
 
     pub fn parse_begin(&mut self) -> Result<Statement, ParserError> {
-        if dialect_of!(self is SnowflakeDialect | BigQueryDialect) {
-            return self.parse_begin_exception_end();
-        }
-
         let modifier = if !self.dialect.supports_start_transaction_modifier() {
             None
         } else if self.parse_keyword(Keyword::DEFERRED) {

tests/sqlparser_common.rs

@@ -8592,7 +8592,10 @@ fn lateral_function() {
 #[test]
 fn parse_start_transaction() {
     let dialects = all_dialects_except(|d|
-        // BigQuery does not support this syntax
+        // BigQuery and Snowflake does not support this syntax
+        //
+        // BigQuery: <https://cloud.google.com/bigquery/docs/reference/standard-sql/procedural-language#begin_transaction>
+        // Snowflake: <https://docs.snowflake.com/en/sql-reference/sql/begin>
         d.is::<BigQueryDialect>() || d.is::<SnowflakeDialect>());
     match dialects
         .verified_stmt("START TRANSACTION READ ONLY, READ WRITE, ISOLATION LEVEL SERIALIZABLE")