feat: introduce SubstraitSqlDialect

Author: vbarua

isthmus/src/main/java/io/substrait/isthmus/SubstraitToSql.java

@@ -2,14 +2,9 @@
 
 import io.substrait.relation.Rel;
 import java.util.List;
-import java.util.function.UnaryOperator;
 import org.apache.calcite.prepare.CalciteCatalogReader;
 import org.apache.calcite.prepare.Prepare;
 import org.apache.calcite.rel.RelNode;
-import org.apache.calcite.rel.rel2sql.RelToSqlConverter;
-import org.apache.calcite.sql.SqlDialect;
-import org.apache.calcite.sql.SqlNode;
-import org.apache.calcite.sql.SqlWriterConfig;
 import org.apache.calcite.sql.parser.SqlParseException;
 
 public class SubstraitToSql extends SqlConverterBase {
@@ -27,39 +22,4 @@ public RelNode substraitRelToCalciteRel(Rel relRoot, List<String> tables)
   public RelNode substraitRelToCalciteRel(Rel relRoot, Prepare.CatalogReader catalog) {
     return SubstraitRelNodeConverter.convert(relRoot, relOptCluster, catalog, parserConfig);
   }
-
-  // DEFAULT_SQL_DIALECT uses Calcite's EMPTY_CONTEXT with setting:
-  //   identifierQuoteString : null, identifierEscapeQuoteString : null
-  //   quotedCasing : UNCHANGED, unquotedCasing : TO_UPPER
-  //   caseSensitive: true
-  //   supportsApproxCountDistinct is true
-  private static final SqlDialect DEFAULT_SQL_DIALECT =
-      new SqlDialect(SqlDialect.EMPTY_CONTEXT) {
-        @Override
-        public boolean supportsApproxCountDistinct() {
-          return true;
-        }
-      };
-
-  public static String toSql(RelNode root) {
-    return toSql(root, DEFAULT_SQL_DIALECT);
-  }
-
-  public static String toSql(RelNode root, SqlDialect dialect) {
-    return toSql(
-        root,
-        dialect,
-        c ->
-            c.withAlwaysUseParentheses(false)
-                .withSelectListItemsOnSeparateLines(false)
-                .withUpdateSetListNewline(false)
-                .withIndentation(0));
-  }
-
-  private static String toSql(
-      RelNode root, SqlDialect dialect, UnaryOperator<SqlWriterConfig> transform) {
-    final RelToSqlConverter converter = new RelToSqlConverter(dialect);
-    final SqlNode sqlNode = converter.visitRoot(root).asStatement();
-    return sqlNode.toSqlString(c -> transform.apply(c.withDialect(dialect))).getSql();
-  }
 }

isthmus/src/main/java/io/substrait/isthmus/sql/SubstraitSqlDialect.java

@@ -0,0 +1,39 @@
+package io.substrait.isthmus.sql;
+
+import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.rel.rel2sql.RelToSqlConverter;
+import org.apache.calcite.sql.SqlDialect;
+import org.apache.calcite.sql.SqlNode;
+import org.apache.calcite.sql.util.SqlString;
+
+/**
+ * {@link SqlDialect} used by Isthmus for parsing
+ *
+ * <p>Intended primarily for internal testing
+ */
+public class SubstraitSqlDialect extends SqlDialect {
+
+  public static SqlDialect.Context DEFAULT_CONTEXT = SqlDialect.EMPTY_CONTEXT;
+
+  public static SqlDialect DEFAULT = new SubstraitSqlDialect(DEFAULT_CONTEXT);
+
+  public static SqlString toSql(RelNode relNode) {
+    RelToSqlConverter relToSql = new RelToSqlConverter(DEFAULT);
+    SqlNode sqlNode = relToSql.visitRoot(relNode).asStatement();
+    return sqlNode.toSqlString(
+        c ->
+            c.withAlwaysUseParentheses(false)
+                .withSelectListItemsOnSeparateLines(false)
+                .withUpdateSetListNewline(false)
+                .withIndentation(0));
+  }
+
+  public SubstraitSqlDialect(Context context) {
+    super(context);
+  }
+
+  @Override
+  public boolean supportsApproxCountDistinct() {
+    return true;
+  }
+}

isthmus/src/test/java/io/substrait/isthmus/RelCopyOnWriteVisitorTest.java

@@ -7,6 +7,7 @@
 import io.substrait.expression.AggregateFunctionInvocation;
 import io.substrait.expression.Expression;
 import io.substrait.extension.SimpleExtension;
+import io.substrait.isthmus.sql.SubstraitSqlDialect;
 import io.substrait.plan.Plan;
 import io.substrait.plan.ProtoPlanConverter;
 import io.substrait.relation.Aggregate;
@@ -139,7 +140,7 @@ public void approximateCountDistinct() throws IOException, SqlParseException {
             .filter(t -> !t.trim().isBlank())
             .collect(java.util.stream.Collectors.toList());
     RelNode relnodeRoot = new SubstraitToSql().substraitRelToCalciteRel(pojoRel, creates);
-    String newSql = SubstraitToSql.toSql(relnodeRoot);
+    String newSql = SubstraitSqlDialect.toSql(relnodeRoot).getSql();
     assertTrue(newSql.toUpperCase().contains("APPROX_COUNT_DISTINCT"));
   }