Fix SQL syntax error for read-only transactions. Fixes #817

Author: bgrainger

src/MySqlConnector/MySql.Data.MySqlClient/MySqlConnection.cs

@@ -152,7 +152,8 @@ private async ValueTask<MySqlTransaction> BeginTransactionAsync(IsolationLevel i
 					false => " read write",
 					null => "",
 				};
-				cmd.CommandText = $"start transaction{consistentSnapshotText}{readOnlyText};";
+				var separatorText = (consistentSnapshotText.Length == 0 || readOnlyText.Length == 0) ? "" : ",";
+				cmd.CommandText = $"start transaction{consistentSnapshotText}{separatorText}{readOnlyText};";
 				await cmd.ExecuteNonQueryAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
 			}
 

tests/SideBySide/Transaction.cs

@@ -138,6 +138,14 @@ public void ReadOnlyTransaction()
 			Assert.Equal(MySqlErrorCode.CannotExecuteInReadOnlyTransaction, (MySqlErrorCode) exception.Number);
 		}
 
+		[Fact]
+		public void ReadOnlySnapshotTransaction()
+		{
+			using var trans = m_connection.BeginTransaction(IsolationLevel.Snapshot, isReadOnly: true);
+			var exception = Assert.Throws<MySqlException>(() => m_connection.Execute("insert into transactions_test values(1), (2)", transaction: trans));
+			Assert.Equal(MySqlErrorCode.CannotExecuteInReadOnlyTransaction, (MySqlErrorCode) exception.Number);
+		}
+
 		[Fact]
 		public void ReadWriteTransaction()
 		{