refactor: unify aggregate and window functions in window handling (#170)

feat: allow window function operands beyond just column references
fix: invocation was not set when building WindowFunction proto message

BREAKING CHANGE:
* Window and WindowFunction have been merged into WindowFunctionInvocation
* WindowFunctionInvocation is now an inner class of expression
* WindowFunctionInvocation now implements Expression.
* Expression visitor now visits WindowFunctionInvocation
* WindowFunctionConvert constructor requires fewer arguments
* windowCreator has additional fields
* POJO WindowBound offset must now be a long, better reflecting spec

core/src/main/java/io/substrait/expression/AbstractExpressionVisitor.java

@@ -139,6 +139,11 @@ public OUTPUT visit(Expression.ScalarFunctionInvocation expr) throws EXCEPTION {
     return visitFallback(expr);
   }
 
+  @Override
+  public OUTPUT visit(Expression.WindowFunctionInvocation expr) throws EXCEPTION {
+    return visitFallback(expr);
+  }
+
   @Override
   public OUTPUT visit(Expression.Cast expr) throws EXCEPTION {
     return visitFallback(expr);
@@ -173,9 +178,4 @@ public OUTPUT visit(Expression.ScalarSubquery expr) throws EXCEPTION {
   public OUTPUT visit(Expression.InPredicate expr) throws EXCEPTION {
     return visitFallback(expr);
   }
-
-  @Override
-  public OUTPUT visit(Expression.Window expr) throws EXCEPTION {
-    return visitFallback(expr);
-  }
 }

core/src/main/java/io/substrait/expression/Expression.java

@@ -3,15 +3,12 @@
 import com.google.protobuf.ByteString;
 import io.substrait.extension.SimpleExtension;
 import io.substrait.proto.AggregateFunction;
-import io.substrait.relation.Aggregate;
 import io.substrait.relation.Rel;
 import io.substrait.type.Type;
 import java.nio.ByteBuffer;
 import java.util.List;
 import java.util.Map;
-import java.util.Optional;
 import java.util.UUID;
-import javax.annotation.Nullable;
 import org.immutables.value.Value;
 
 @Value.Enclosing
@@ -573,6 +570,42 @@ public <R, E extends Throwable> R accept(ExpressionVisitor<R, E> visitor) throws
     }
   }
 
+  @Value.Immutable
+  abstract class WindowFunctionInvocation implements Expression {
+
+    public abstract SimpleExtension.WindowFunctionVariant declaration();
+
+    public abstract List<FunctionArg> arguments();
+
+    public abstract Map<String, FunctionOption> options();
+
+    public abstract AggregationPhase aggregationPhase();
+
+    public abstract List<Expression> partitionBy();
+
+    public abstract List<SortField> sort();
+
+    public abstract WindowBound lowerBound();
+
+    public abstract WindowBound upperBound();
+
+    public abstract Type outputType();
+
+    public Type getType() {
+      return outputType();
+    }
+
+    public abstract AggregationInvocation invocation();
+
+    public static ImmutableExpression.WindowFunctionInvocation.Builder builder() {
+      return ImmutableExpression.WindowFunctionInvocation.builder();
+    }
+
+    public <R, E extends Throwable> R accept(ExpressionVisitor<R, E> visitor) throws E {
+      return visitor.visit(this);
+    }
+  }
+
   @Value.Immutable
   abstract static class SingleOrList implements Expression {
     public abstract Expression condition();
@@ -684,41 +717,6 @@ public <R, E extends Throwable> R accept(ExpressionVisitor<R, E> visitor) throws
     }
   }
 
-  @Value.Immutable
-  abstract static class Window implements Expression {
-    @Nullable
-    public abstract Aggregate.Measure aggregateFunction();
-
-    @Nullable
-    public abstract WindowFunction windowFunction();
-
-    public abstract List<Expression> partitionBy();
-
-    public abstract List<SortField> orderBy();
-
-    public abstract WindowBound lowerBound();
-
-    public abstract WindowBound upperBound();
-
-    public abstract boolean hasNormalAggregateFunction();
-
-    public static ImmutableExpression.Window.Builder builder() {
-      return ImmutableExpression.Window.builder();
-    }
-
-    public <R, E extends Throwable> R accept(ExpressionVisitor<R, E> visitor) throws E {
-      return visitor.visit(this);
-    }
-  }
-
-  @Value.Immutable
-  public abstract static class WindowFunction {
-    public abstract WindowFunctionInvocation getFunction();
-
-    public abstract Optional<Expression> getPreMeasureFilter();
-    /** public static ImmutableMeasure.Builder builder() { return ImmutableMeasure.builder(); } */
-  }
-
   enum PredicateOp {
     PREDICATE_OP_UNSPECIFIED(
         io.substrait.proto.Expression.Subquery.SetPredicate.PredicateOp.PREDICATE_OP_UNSPECIFIED),

core/src/main/java/io/substrait/expression/ExpressionCreator.java

@@ -313,36 +313,48 @@ public static AggregateFunctionInvocation aggregateFunction(
         .build();
   }
 
-  public static WindowFunctionInvocation windowFunction(
+  public static Expression.WindowFunctionInvocation windowFunction(
       SimpleExtension.WindowFunctionVariant declaration,
       Type outputType,
       Expression.AggregationPhase phase,
       List<Expression.SortField> sort,
       Expression.AggregationInvocation invocation,
+      List<Expression> partitionBy,
+      WindowBound lowerBound,
+      WindowBound upperBound,
       Iterable<? extends FunctionArg> arguments) {
-    return WindowFunctionInvocation.builder()
+    return Expression.WindowFunctionInvocation.builder()
         .declaration(declaration)
         .outputType(outputType)
         .aggregationPhase(phase)
         .sort(sort)
+        .partitionBy(partitionBy)
+        .lowerBound(lowerBound)
+        .upperBound(upperBound)
         .invocation(invocation)
         .addAllArguments(arguments)
         .build();
   }
 
-  public static WindowFunctionInvocation windowFunction(
+  public static Expression.WindowFunctionInvocation windowFunction(
       SimpleExtension.WindowFunctionVariant declaration,
       Type outputType,
       Expression.AggregationPhase phase,
       List<Expression.SortField> sort,
       Expression.AggregationInvocation invocation,
+      List<Expression> partitionBy,
+      WindowBound lowerBound,
+      WindowBound upperBound,
       FunctionArg... arguments) {
-    return WindowFunctionInvocation.builder()
+    return Expression.WindowFunctionInvocation.builder()
         .declaration(declaration)
         .outputType(outputType)
         .aggregationPhase(phase)
         .sort(sort)
         .invocation(invocation)
+        .partitionBy(partitionBy)
+        .lowerBound(lowerBound)
+        .upperBound(upperBound)
         .addArguments(arguments)
         .build();
   }

core/src/main/java/io/substrait/expression/ExpressionVisitor.java

@@ -57,6 +57,8 @@ public interface ExpressionVisitor<R, E extends Throwable> {
 
   R visit(Expression.ScalarFunctionInvocation expr) throws E;
 
+  R visit(Expression.WindowFunctionInvocation expr) throws E;
+
   R visit(Expression.Cast expr) throws E;
 
   R visit(Expression.SingleOrList expr) throws E;
@@ -70,6 +72,4 @@ public interface ExpressionVisitor<R, E extends Throwable> {
   R visit(Expression.ScalarSubquery expr) throws E;
 
   R visit(Expression.InPredicate expr) throws E;
-
-  R visit(Expression.Window expr) throws E;
 }

core/src/main/java/io/substrait/expression/WindowBound.java

@@ -45,7 +45,7 @@ public BoundedKind boundedKind() {
 
     public abstract Direction direction();
 
-    public abstract Expression offset();
+    public abstract long offset();
 
     public static ImmutableWindowBound.BoundedWindowBound.Builder builder() {
       return ImmutableWindowBound.BoundedWindowBound.builder();

core/src/main/java/io/substrait/expression/proto/ExpressionProtoConverter.java

@@ -1,14 +1,15 @@
 package io.substrait.expression.proto;
 
-import io.substrait.expression.AbstractExpressionVisitor;
 import io.substrait.expression.ExpressionVisitor;
 import io.substrait.expression.FieldReference;
 import io.substrait.expression.FunctionArg;
 import io.substrait.expression.WindowBound;
 import io.substrait.extension.ExtensionCollector;
 import io.substrait.proto.Expression;
+import io.substrait.proto.FunctionArgument;
 import io.substrait.proto.Rel;
 import io.substrait.proto.SortField;
+import io.substrait.proto.Type;
 import io.substrait.relation.RelVisitor;
 import io.substrait.type.proto.TypeProtoConverter;
 import java.util.List;
@@ -415,99 +416,48 @@ public Expression visit(io.substrait.expression.Expression.InPredicate expr)
         .build();
   }
 
-  public Expression visit(io.substrait.expression.Expression.Window expr) throws RuntimeException {
-    var partExps =
+  public Expression visit(io.substrait.expression.Expression.WindowFunctionInvocation expr)
+      throws RuntimeException {
+    var argVisitor = FunctionArg.toProto(typeProtoConverter, this);
+    List<FunctionArgument> args =
+        expr.arguments().stream()
+            .map(a -> a.accept(expr.declaration(), 0, argVisitor))
+            .collect(java.util.stream.Collectors.toList());
+    Type outputType = expr.getType().accept(typeProtoConverter);
+
+    List<Expression> partitionExprs =
         expr.partitionBy().stream()
             .map(e -> e.accept(this))
             .collect(java.util.stream.Collectors.toList());
-    var outputType = expr.getType().accept(typeProtoConverter);
-    var builder = Expression.WindowFunction.newBuilder().setOutputType(outputType);
-    if (expr.hasNormalAggregateFunction()) {
-      var aggMeasureFunc = expr.aggregateFunction().getFunction();
-      var funcReference = extensionCollector.getFunctionReference(aggMeasureFunc.declaration());
-      var argVisitor = FunctionArg.toProto(typeProtoConverter, this);
-      var args =
-          aggMeasureFunc.arguments().stream()
-              .map(a -> a.accept(aggMeasureFunc.declaration(), 0, argVisitor))
-              .collect(java.util.stream.Collectors.toList());
-      builder
-          .setFunctionReference(funcReference)
-          .setPhase(aggMeasureFunc.aggregationPhase().toProto())
-          .addAllArguments(args);
-    } else {
-      var windowFunc = expr.windowFunction().getFunction();
-      var funcReference = extensionCollector.getFunctionReference(windowFunc.declaration());
-      var argVisitor = FunctionArg.toProto(typeProtoConverter, this);
-      var args =
-          windowFunc.arguments().stream()
-              .map(a -> a.accept(windowFunc.declaration(), 0, argVisitor))
-              .collect(java.util.stream.Collectors.toList());
-      builder
-          .setFunctionReference(funcReference)
-          .setPhase(windowFunc.aggregationPhase().toProto())
-          .addAllArguments(args);
-    }
-    var sortFields =
-        expr.orderBy().stream()
+
+    List<SortField> sortFields =
+        expr.sort().stream()
             .map(
-                s -> {
-                  return SortField.newBuilder()
-                      .setDirection(s.direction().toProto())
-                      .setExpr(s.expr().accept(this))
-                      .build();
-                })
+                s ->
+                    SortField.newBuilder()
+                        .setDirection(s.direction().toProto())
+                        .setExpr(s.expr().accept(this))
+                        .build())
             .collect(java.util.stream.Collectors.toList());
-    var upperBound = toBound(expr.upperBound());
-    var lowerBound = toBound(expr.lowerBound());
+
+    Expression.WindowFunction.Bound upperBound = toBound(expr.upperBound());
+    Expression.WindowFunction.Bound lowerBound = toBound(expr.lowerBound());
+
     return Expression.newBuilder()
         .setWindowFunction(
-            builder
-                .addAllPartitions(partExps)
+            Expression.WindowFunction.newBuilder()
+                .setFunctionReference(extensionCollector.getFunctionReference(expr.declaration()))
+                .addAllArguments(args)
+                .setOutputType(outputType)
+                .setPhase(expr.aggregationPhase().toProto())
+                .setInvocation(expr.invocation().toProto())
                 .addAllSorts(sortFields)
+                .addAllPartitions(partitionExprs)
                 .setLowerBound(lowerBound)
-                .setUpperBound(upperBound)
-                .build())
+                .setUpperBound(upperBound))
         .build();
   }
 
-  private static class LiteralToWindowBoundOffset
-      extends AbstractExpressionVisitor<Long, RuntimeException> {
-
-    @Override
-    public Long visitFallback(io.substrait.expression.Expression expr) {
-      throw new RuntimeException(
-          String.format("Expected positive integer for Window Bound offset, received: %s", expr));
-    }
-
-    private static long offsetIsPositive(long offset) {
-      if (offset >= 1) {
-        return offset;
-      }
-      throw new RuntimeException(
-          String.format("Expected positive offset for Window Bound offset, recieved: %d", offset));
-    }
-
-    @Override
-    public Long visit(io.substrait.expression.Expression.I8Literal expr) throws RuntimeException {
-      return offsetIsPositive(expr.value());
-    }
-
-    @Override
-    public Long visit(io.substrait.expression.Expression.I16Literal expr) throws RuntimeException {
-      return offsetIsPositive(expr.value());
-    }
-
-    @Override
-    public Long visit(io.substrait.expression.Expression.I32Literal expr) throws RuntimeException {
-      return offsetIsPositive(expr.value());
-    }
-
-    @Override
-    public Long visit(io.substrait.expression.Expression.I64Literal expr) throws RuntimeException {
-      return offsetIsPositive(expr.value());
-    }
-  }
-
   private Expression.WindowFunction.Bound toBound(io.substrait.expression.WindowBound windowBound) {
     var boundedKind = windowBound.boundedKind();
     return switch (boundedKind) {
@@ -517,7 +467,7 @@ private Expression.WindowFunction.Bound toBound(io.substrait.expression.WindowBo
       case BOUNDED -> {
         WindowBound.BoundedWindowBound boundedWindowBound =
             (WindowBound.BoundedWindowBound) windowBound;
-        var offset = boundedWindowBound.offset().accept(new LiteralToWindowBoundOffset());
+        var offset = boundedWindowBound.offset();
         yield switch (boundedWindowBound.direction()) {
           case PRECEDING -> Expression.WindowFunction.Bound.newBuilder()
               .setPreceding(