fix(javadoc): partial isthmus

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

@@ -23,6 +23,21 @@
 import org.apache.calcite.sql.type.SqlTypeFamily;
 import org.apache.calcite.sql.type.SqlTypeName;
 
+/**
+ * Utility class for converting Substrait {@link SimpleExtension} function definitions (scalar and
+ * aggregate) into Calcite {@link SqlOperator}s.
+ *
+ * <p>This enables Calcite to recognize and use Substrait-defined functions during query planning
+ * and execution. Conversion includes:
+ *
+ * <ul>
+ *   <li>Mapping Substrait types to Calcite {@link SqlTypeName}
+ *   <li>Building {@link SqlFunction} instances with proper argument families
+ *   <li>Inferring return types based on Substrait type expressions and nullability rules
+ * </ul>
+ *
+ * <p>Currently supports scalar and aggregate functions; window functions are not yet implemented.
+ */
 public final class SimpleExtensionToSqlOperator {
 
   private static final RelDataTypeFactory DEFAULT_TYPE_FACTORY =
@@ -32,15 +47,40 @@ public final class SimpleExtensionToSqlOperator {
 
   private SimpleExtensionToSqlOperator() {}
 
+  /**
+   * Converts all functions in a Substrait {@link SimpleExtension.ExtensionCollection} (scalar and
+   * aggregate) into Calcite {@link SqlOperator}s using the default type factory.
+   *
+   * @param collection The Substrait extension collection containing function definitions.
+   * @return A list of Calcite {@link SqlOperator}s corresponding to the Substrait functions.
+   */
   public static List<SqlOperator> from(SimpleExtension.ExtensionCollection collection) {
     return from(collection, DEFAULT_TYPE_FACTORY);
   }
 
+  /**
+   * Converts all functions in a Substrait {@link SimpleExtension.ExtensionCollection} (scalar and
+   * aggregate) into Calcite {@link SqlOperator}s using a provided type factory.
+   *
+   * @param collection The Substrait extension collection containing function definitions.
+   * @param typeFactory Calcite {@link RelDataTypeFactory} for type creation and inference.
+   * @return A list of Calcite {@link SqlOperator}s corresponding to the Substrait functions.
+   */
   public static List<SqlOperator> from(
       SimpleExtension.ExtensionCollection collection, RelDataTypeFactory typeFactory) {
     return from(collection, typeFactory, TypeConverter.DEFAULT);
   }
 
+  /**
+   * Converts all functions in a Substrait {@link SimpleExtension.ExtensionCollection} (scalar and
+   * aggregate) into Calcite {@link SqlOperator}s with a custom type factory and {@link
+   * TypeConverter}.
+   *
+   * @param collection The Substrait extension collection containing function definitions.
+   * @param typeFactory Calcite {@link RelDataTypeFactory} for type creation and inference.
+   * @param typeConverter Converter for Substrait/Calcite type mappings.
+   * @return A list of Calcite {@link SqlOperator}s corresponding to the Substrait functions.
+   */
   public static List<SqlOperator> from(
       SimpleExtension.ExtensionCollection collection,
       RelDataTypeFactory typeFactory,

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

@@ -14,20 +14,41 @@
 import org.apache.calcite.sql.parser.SqlParser;
 import org.apache.calcite.sql2rel.SqlToRelConverter;
 
+/**
+ * Base class for Substrait SQL conversion pipelines.
+ *
+ * <p>Configures Calcite parser, connection, planner, and cluster. Holds the Substrait extensions
+ * and feature flags. Subclasses can build conversions from SQL to Calcite/Substrait using this
+ * shared setup.
+ */
 public class SqlConverterBase {
   protected final ConverterProvider converterProvider;
 
+  /** Default Calcite connection config (case-insensitive). */
   public static final CalciteConnectionConfig CONNECTION_CONFIG =
       CalciteConnectionConfig.DEFAULT.set(
           CalciteConnectionProperty.CASE_SENSITIVE, Boolean.FALSE.toString());
 
+  /** Calcite type factory using the Substrait type system. */
   final RelDataTypeFactory factory;
+
+  /** Calcite optimization cluster with planner, type factory, and RexBuilder. */
   final RelOptCluster relOptCluster;
+
+  /** Connection configuration used for SQL parsing and validation. */
   final CalciteConnectionConfig config;
+
+  /** Configuration for SQL-to-Rel conversion. */
   final SqlToRelConverter.Config converterConfig;
 
+  /** Parser configuration, including casing and DDL parser factory. */
   final SqlParser.Config parserConfig;
 
+  /**
+   * Creates a converter base with explicit features and extensions.
+   *
+   * @param converterProvider Converter Provider for configuration
+   */
   protected SqlConverterBase(ConverterProvider converterProvider) {
     this.converterProvider = converterProvider;
     this.factory = converterProvider.getTypeFactory();

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

@@ -27,25 +27,47 @@
 import org.apache.calcite.sql2rel.SqlToRelConverter;
 import org.apache.calcite.sql2rel.StandardConvertletTable;
 
+/**
+ * Converts SQL expressions to Substrait {@link io.substrait.proto.ExtendedExpression} payloads.
+ *
+ * <p>Supports optional CREATE TABLE statements to provide schema and column bindings for expression
+ * validation and Rex conversion.
+ */
 public class SqlExpressionToSubstrait extends SqlConverterBase {
 
+  /** Converter for RexNodes to Substrait expressions. */
   protected final RexExpressionConverter rexConverter;
 
+  /** Creates a converter with default configuration. */
   public SqlExpressionToSubstrait() {
     this(new ConverterProvider());
   }
 
+  /**
+   * Creates a converter with the given converter provider.
+   *
+   * @param converterProvider Converter Provider to use for configuration
+   */
   public SqlExpressionToSubstrait(ConverterProvider converterProvider) {
     super(converterProvider);
     this.rexConverter = new RexExpressionConverter(converterProvider.getScalarFunctionConverter());
   }
 
+  /** Bundled result carrying validator, catalog reader, and name/type and name/node maps. */
   private static final class Result {
     final SqlValidator validator;
     final CalciteCatalogReader catalogReader;
     final Map<String, RelDataType> nameToTypeMap;
     final Map<String, RexNode> nameToNodeMap;
 
+    /**
+     * Creates a result bundle.
+     *
+     * @param validator SQL validator
+     * @param catalogReader Calcite catalog reader
+     * @param nameToTypeMap mapping from column name to Calcite type
+     * @param nameToNodeMap mapping from column name to Rex input ref
+     */
     Result(
         SqlValidator validator,
         CalciteCatalogReader catalogReader,
@@ -59,25 +81,25 @@ private static final class Result {
   }
 
   /**
-   * Converts the given SQL expression to an {@link io.substrait.proto.ExtendedExpression }
+   * Converts a single SQL expression to a Substrait {@link io.substrait.proto.ExtendedExpression}.
    *
    * @param sqlExpression a SQL expression
    * @param createStatements table creation statements defining fields referenced by the expression
-   * @return a {@link io.substrait.proto.ExtendedExpression }
-   * @throws SqlParseException
+   * @return the Substrait extended expression proto
+   * @throws SqlParseException if parsing or validation fails
    */
   public io.substrait.proto.ExtendedExpression convert(
       String sqlExpression, List<String> createStatements) throws SqlParseException {
     return convert(new String[] {sqlExpression}, createStatements);
   }
 
   /**
-   * Converts the given SQL expressions to an {@link io.substrait.proto.ExtendedExpression }
+   * Converts multiple SQL expressions to a Substrait {@link io.substrait.proto.ExtendedExpression}.
    *
-   * @param sqlExpressions an array of SQL expressions
-   * @param createStatements table creation statements defining fields referenced by the expression
-   * @return a {@link io.substrait.proto.ExtendedExpression }
-   * @throws SqlParseException
+   * @param sqlExpressions array of SQL expressions
+   * @param createStatements table creation statements defining fields referenced by the expressions
+   * @return the Substrait extended expression proto
+   * @throws SqlParseException if parsing or validation fails
    */
   public io.substrait.proto.ExtendedExpression convert(
       String[] sqlExpressions, List<String> createStatements) throws SqlParseException {
@@ -90,6 +112,17 @@ public io.substrait.proto.ExtendedExpression convert(
         result.nameToNodeMap);
   }
 
+  /**
+   * Converts the given SQL expressions using the provided validator/catalog and column bindings.
+   *
+   * @param sqlExpressions array of SQL expressions
+   * @param validator SQL validator
+   * @param catalogReader Calcite catalog reader
+   * @param nameToTypeMap mapping from column name to Calcite type
+   * @param nameToNodeMap mapping from column name to Rex input ref
+   * @return the Substrait extended expression proto
+   * @throws SqlParseException if parsing or validation fails
+   */
   private io.substrait.proto.ExtendedExpression executeInnerSQLExpressions(
       String[] sqlExpressions,
       SqlValidator validator,
@@ -120,6 +153,17 @@ private io.substrait.proto.ExtendedExpression executeInnerSQLExpressions(
     return new ExtendedExpressionProtoConverter().toProto(extendedExpression.build());
   }
 
+  /**
+   * Parses and validates a SQL expression, then converts it to a {@link RexNode}.
+   *
+   * @param sql SQL expression string
+   * @param validator SQL validator
+   * @param catalogReader Calcite catalog reader
+   * @param nameToTypeMap mapping from column name to Calcite type
+   * @param nameToNodeMap mapping from column name to Rex input ref
+   * @return the converted RexNode
+   * @throws SqlParseException if parsing or validation fails
+   */
   private RexNode sqlToRexNode(
       String sql,
       SqlValidator validator,
@@ -141,6 +185,13 @@ private RexNode sqlToRexNode(
     return converter.convertExpression(validSqlNode, nameToNodeMap);
   }
 
+  /**
+   * Registers tables from CREATE statements and prepares validator, catalog, and column bindings.
+   *
+   * @param tables list of CREATE TABLE statements; may be null
+   * @return result bundle containing validator, catalog reader, and name/type and name/node maps
+   * @throws SqlParseException if any CREATE statement is invalid
+   */
   private Result registerCreateTablesForExtendedExpression(List<String> tables)
       throws SqlParseException {
     Map<String, RelDataType> nameToTypeMap = new LinkedHashMap<>();
@@ -177,6 +228,12 @@ private Result registerCreateTablesForExtendedExpression(List<String> tables)
     return new Result(validator, catalogReader, nameToTypeMap, nameToNodeMap);
   }
 
+  /**
+   * Converts a name-to-type map into a {@link NamedStruct} in Substrait types.
+   *
+   * @param nameToTypeMap mapping from column name to Calcite type
+   * @return a {@link NamedStruct} with non-nullable struct type
+   */
   private NamedStruct toNamedStruct(Map<String, RelDataType> nameToTypeMap) {
     ArrayList<String> names = new ArrayList<String>();
     ArrayList<Type> types = new ArrayList<Type>();

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

@@ -19,10 +19,16 @@
 public class SqlToSubstrait extends SqlConverterBase {
   private final SqlOperatorTable operatorTable;
 
+  /** Creates a SQL-to-Substrait converter using the default configuration. */
   public SqlToSubstrait() {
     this(new ConverterProvider());
   }
 
+  /**
+   * Creates a SQL-to-Substrait converter with explicit extensions and features.
+   *
+   * @param converterProvider Converter Provider for the configuration
+   */
   public SqlToSubstrait(ConverterProvider converterProvider) {
     super(converterProvider);
     this.operatorTable = converterProvider.getSqlOperatorTable();

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

@@ -90,17 +90,36 @@
 public class SubstraitRelNodeConverter
     extends AbstractRelVisitor<RelNode, SubstraitRelNodeConverter.Context, RuntimeException> {
 
+  /** Calcite type factory used to construct row and field types. */
   protected final RelDataTypeFactory typeFactory;
 
+  /** Converter for Substrait scalar functions to Calcite operators. */
   protected final ScalarFunctionConverter scalarFunctionConverter;
+
+  /** Converter for Substrait aggregate functions to Calcite operators. */
   protected final AggregateFunctionConverter aggregateFunctionConverter;
+
+  /** Converts Substrait {@code Expression}s into Calcite {@code RexNode}s. */
   protected final ExpressionRexConverter expressionRexConverter;
 
+  /** Calcite {@link RelBuilder} used to construct relational expressions during conversion. */
   protected final RelBuilder relBuilder;
+
+  /** Calcite {@link RexBuilder} used to build Rex nodes (e.g., input refs, literals). */
   protected final RexBuilder rexBuilder;
+
+  /** Type converter to translate between Calcite and Substrait type systems. */
   private final TypeConverter typeConverter;
 
-  /** Use {@link #SubstraitRelNodeConverter(RelBuilder, ConverterProvider)} instead */
+  /**
+   * Creates a new SubstraitRelNodeConverter with the specified extensions, type factory, and
+   * relation builder.
+   *
+   * @param extensions the Substrait extension collection
+   * @param typeFactory the Calcite type factory
+   * @param relBuilder the Calcite relation builder
+   * @deprecated Use {@link #SubstraitRelNodeConverter(RelBuilder, ConverterProvider)} instead
+   */
   @Deprecated
   public SubstraitRelNodeConverter(
       SimpleExtension.ExtensionCollection extensions,
@@ -109,6 +128,13 @@ public SubstraitRelNodeConverter(
     this(relBuilder, new ConverterProvider(extensions, typeFactory));
   }
 
+  /**
+   * Creates a new SubstraitRelNodeConverter with the specified relation builder and converter
+   * provider.
+   *
+   * @param relBuilder the Calcite relation builder
+   * @param converterProvider the converter provider containing configuration and converters
+   */
   public SubstraitRelNodeConverter(RelBuilder relBuilder, ConverterProvider converterProvider) {
     this.typeFactory = converterProvider.getTypeFactory();
     this.typeConverter = converterProvider.getTypeConverter();
@@ -119,6 +145,14 @@ public SubstraitRelNodeConverter(RelBuilder relBuilder, ConverterProvider conver
     this.expressionRexConverter = converterProvider.getExpressionRexConverter(this);
   }
 
+  /**
+   * Converts a Substrait {@link Rel} plan to a Calcite {@link RelNode}.
+   *
+   * @param relRoot the root Substrait relation to convert
+   * @param catalogReader the Calcite catalog reader for schema resolution
+   * @param converterProvider the converter provider containing configuration and converters
+   * @return the converted Calcite {@link RelNode}
+   */
   public static RelNode convert(
       Rel relRoot, Prepare.CatalogReader catalogReader, ConverterProvider converterProvider) {
     RelBuilder relBuilder =
@@ -736,6 +770,16 @@ public RelNode visitFallback(Rel rel, Context context) throws RuntimeException {
             rel, rel.getClass().getCanonicalName(), this.getClass().getCanonicalName()));
   }
 
+  /**
+   * Applies an optional field remap to the given node.
+   *
+   * <p>If {@code remap} is present, the node is projected according to the provided indices;
+   * otherwise the original node is returned unchanged.
+   *
+   * @param relNode the node to remap
+   * @param remap optional field index remap
+   * @return remapped node or original node if no remap is present
+   */
   protected RelNode applyRemap(RelNode relNode, Optional<Rel.Remap> remap) {
     if (remap.isPresent()) {
       return applyRemap(relNode, remap.get());
@@ -759,8 +803,10 @@ private RelNode applyRemap(RelNode relNode, Rel.Remap remap) {
 
   /** A shared context for the Substrait to RelNode conversion. */
   public static class Context implements VisitationContext {
+    /** Stack of outer row type range maps used to resolve correlated references. */
     protected final Stack<RangeMap<Integer, RelDataType>> outerRowTypes = new Stack<>();
 
+    /** Stack of correlation ids collected while visiting subqueries. */
     protected final Stack<java.util.Set<CorrelationId>> correlationIds = new Stack<>();
 
     private int subqueryDepth;
@@ -798,6 +844,7 @@ public void pushOuterRowType(final RelDataType... inputs) {
       this.correlationIds.push(new HashSet<>());
     }
 
+    /** Pops the most recent outer row type from the stack. */
     public void popOuterRowType() {
       outerRowTypes.pop();
     }