fix: also output old structures

Signed-off-by: Niels Pardon <par@zurich.ibm.com>

Author: nielspardon

core/src/main/java/io/substrait/relation/RelProtoConverter.java

@@ -215,6 +215,8 @@ private AggregateRel.Measure toProto(Aggregate.Measure measure) {
   private AggregateRel.Grouping toProto(
       Aggregate.Grouping grouping, List<Expression> uniqueGroupingExpressions) {
     return AggregateRel.Grouping.newBuilder()
+        .addAllGroupingExpressions(
+            grouping.getExpressions().stream().map(this::toProto).collect(Collectors.toList()))
         .addAllExpressionReferences(
             grouping.getExpressions().stream()
                 .map(e -> uniqueGroupingExpressions.indexOf(e))

core/src/test/java/io/substrait/relation/AggregateRelTest.java

@@ -102,9 +102,9 @@ void testDeprecatedGroupingExpressionConversion() {
         roundtripAgg.getGroupingExpressionsCount(),
         "grouping expressions count of aggregate should be 2");
     assertEquals(
-        0,
+        2,
         roundtripAgg.getGroupings(0).getGroupingExpressionsCount(),
-        "grouping expressions count of grouping should be 0");
+        "grouping expressions count of grouping should be 2");
     assertEquals(
         2,
         roundtripAgg.getGroupings(0).getExpressionReferencesCount(),
@@ -157,9 +157,9 @@ void testAggregateWithSingleGrouping() {
         roundtripAgg.getGroupingExpressionsCount(),
         "grouping expressions count of aggregate should be 2");
     assertEquals(
-        0,
+        2,
         roundtripAgg.getGroupings(0).getGroupingExpressionsCount(),
-        "grouping expressions count of grouping should be 0");
+        "grouping expressions count of grouping should be 2");
     assertEquals(
         2,
         roundtripAgg.getGroupings(0).getExpressionReferencesCount(),
@@ -217,9 +217,9 @@ void testAggregateWithMultipleGroupings() {
         roundtripAgg.getGroupingExpressionsCount(),
         "grouping expressions count of aggregate should be 2");
     assertEquals(
-        0,
+        2,
         roundtripAgg.getGroupings(0).getGroupingExpressionsCount(),
-        "grouping expressions count of grouping should be 0");
+        "grouping expressions count of grouping should be 2");
     assertEquals(
         2,
         roundtripAgg.getGroupings(0).getExpressionReferencesCount(),