refactor: move DialectUnparser to query.rs and box large enum variant

Move DialectUnparser and SqlDialect::unparser() from spark_dialect.rs
to query.rs to co-locate with the SqlDialect enum. Box the Spark
CustomDialect variant to fix clippy::large_enum_variant lint.

Co-authored-by: Isaac

Author: Yu Chen

crates/lance-graph/src/query.rs

@@ -9,8 +9,13 @@ use crate::config::GraphConfig;
 use crate::error::{GraphError, Result};
 use crate::logical_plan::LogicalPlanner;
 use crate::parser::parse_cypher_query;
+use crate::spark_dialect::build_spark_dialect;
 use arrow_array::RecordBatch;
 use arrow_schema::{Field, Schema, SchemaRef};
+use datafusion_sql::unparser::dialect::{
+    CustomDialect, DefaultDialect, MySqlDialect, PostgreSqlDialect, SqliteDialect,
+};
+use datafusion_sql::unparser::Unparser;
 use lance_graph_catalog::DirNamespace;
 use lance_namespace::models::DescribeTableRequest;
 use std::collections::{HashMap, HashSet};
@@ -32,6 +37,40 @@ pub enum SqlDialect {
     Sqlite,
 }
 
+/// Wrapper to hold the concrete dialect type and provide an `Unparser` reference.
+pub enum DialectUnparser {
+    Default(DefaultDialect),
+    Spark(Box<CustomDialect>),
+    PostgreSql(PostgreSqlDialect),
+    MySql(MySqlDialect),
+    Sqlite(SqliteDialect),
+}
+
+impl DialectUnparser {
+    pub fn as_unparser(&self) -> Unparser<'_> {
+        match self {
+            DialectUnparser::Default(d) => Unparser::new(d),
+            DialectUnparser::Spark(d) => Unparser::new(d.as_ref()),
+            DialectUnparser::PostgreSql(d) => Unparser::new(d),
+            DialectUnparser::MySql(d) => Unparser::new(d),
+            DialectUnparser::Sqlite(d) => Unparser::new(d),
+        }
+    }
+}
+
+impl SqlDialect {
+    /// Create a `DialectUnparser` configured for this dialect.
+    pub fn unparser(&self) -> DialectUnparser {
+        match self {
+            SqlDialect::Default => DialectUnparser::Default(DefaultDialect {}),
+            SqlDialect::Spark => DialectUnparser::Spark(Box::new(build_spark_dialect())),
+            SqlDialect::PostgreSql => DialectUnparser::PostgreSql(PostgreSqlDialect {}),
+            SqlDialect::MySql => DialectUnparser::MySql(MySqlDialect {}),
+            SqlDialect::Sqlite => DialectUnparser::Sqlite(SqliteDialect {}),
+        }
+    }
+}
+
 /// Normalize an Arrow schema to have lowercase field names.
 ///
 /// This ensures that column names in the dataset match the normalized

crates/lance-graph/src/spark_dialect.rs

@@ -1,11 +1,10 @@
 // SPDX-License-Identifier: Apache-2.0
 // SPDX-FileCopyrightText: Copyright The Lance Authors
 
-//! SQL dialect support for the DataFusion unparser.
+//! Spark SQL dialect for the DataFusion unparser.
 //!
 //! This module provides a Spark SQL dialect built using DataFusion's
-//! [`CustomDialectBuilder`], and a helper to build an [`Unparser`] for any
-//! supported [`SqlDialect`].
+//! [`CustomDialectBuilder`].
 //!
 //! Key Spark SQL differences from standard SQL:
 //! - Backtick (`` ` ``) identifier quoting
@@ -18,13 +17,9 @@
 
 use datafusion_sql::unparser::dialect::{
     CharacterLengthStyle, CustomDialect, CustomDialectBuilder, DateFieldExtractStyle,
-    DefaultDialect, MySqlDialect, PostgreSqlDialect, SqliteDialect,
 };
-use datafusion_sql::unparser::Unparser;
 use datafusion_sql::sqlparser::ast::{self, Ident, ObjectName, TimezoneInfo};
 
-use crate::query::SqlDialect;
-
 /// Build a Spark SQL dialect using DataFusion's `CustomDialectBuilder`.
 pub fn build_spark_dialect() -> CustomDialect {
     CustomDialectBuilder::new()
@@ -56,40 +51,6 @@ pub fn build_spark_dialect() -> CustomDialect {
         .build()
 }
 
-/// Wrapper to hold the concrete dialect type and provide an `Unparser` reference.
-pub enum DialectUnparser {
-    Default(DefaultDialect),
-    Spark(CustomDialect),
-    PostgreSql(PostgreSqlDialect),
-    MySql(MySqlDialect),
-    Sqlite(SqliteDialect),
-}
-
-impl DialectUnparser {
-    pub fn as_unparser(&self) -> Unparser<'_> {
-        match self {
-            DialectUnparser::Default(d) => Unparser::new(d),
-            DialectUnparser::Spark(d) => Unparser::new(d),
-            DialectUnparser::PostgreSql(d) => Unparser::new(d),
-            DialectUnparser::MySql(d) => Unparser::new(d),
-            DialectUnparser::Sqlite(d) => Unparser::new(d),
-        }
-    }
-}
-
-impl SqlDialect {
-    /// Create a `DialectUnparser` configured for this dialect.
-    pub fn unparser(&self) -> DialectUnparser {
-        match self {
-            SqlDialect::Default => DialectUnparser::Default(DefaultDialect {}),
-            SqlDialect::Spark => DialectUnparser::Spark(build_spark_dialect()),
-            SqlDialect::PostgreSql => DialectUnparser::PostgreSql(PostgreSqlDialect {}),
-            SqlDialect::MySql => DialectUnparser::MySql(MySqlDialect {}),
-            SqlDialect::Sqlite => DialectUnparser::Sqlite(SqliteDialect {}),
-        }
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;