Add expressions support for Virtual Tables

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

@@ -133,7 +133,7 @@ public Rel from(io.substrait.proto.Rel rel) {
   protected Rel newRead(ReadRel rel) {
     if (rel.hasVirtualTable()) {
       var virtualTable = rel.getVirtualTable();
-      if (virtualTable.getValuesCount() == 0) {
+      if (virtualTable.getValuesCount() == 0 && virtualTable.getExpressionsCount() == 0) {
         return newEmptyScan(rel);
       } else {
         return newVirtualTable(rel);
@@ -418,9 +418,11 @@ protected FileOrFiles newFileOrFiles(ReadRel.LocalFiles.FileOrFiles file) {
   protected VirtualTableScan newVirtualTable(ReadRel rel) {
     var virtualTable = rel.getVirtualTable();
     var virtualTableSchema = newNamedStruct(rel);
+
     var converter =
         new ProtoExpressionConverter(lookup, extensions, virtualTableSchema.struct(), this);
-    List<Expression.StructLiteral> structLiterals = new ArrayList<>(virtualTable.getValuesCount());
+
+    List<Expression.StructLiteral> structLiterals = new ArrayList<>(virtualTable.getValuesCount() + virtualTable.getExpressionsCount());
     for (var struct : virtualTable.getValuesList()) {
       structLiterals.add(
           ImmutableExpression.StructLiteral.builder()
@@ -430,6 +432,16 @@ protected VirtualTableScan newVirtualTable(ReadRel rel) {
                       .collect(java.util.stream.Collectors.toList()))
               .build());
     }
+    for (var struct : virtualTable.getExpressionsList()) {
+      structLiterals.add(
+          ImmutableExpression.StructLiteral.builder()
+              .fields(
+                  struct.getFieldsList().stream()
+                      .map(io.substrait.proto.Expression::getLiteral)
+                      .map(converter::from)
+                      .collect(java.util.stream.Collectors.toList()))
+              .build());
+    }
 
     var builder =
         VirtualTableScan.builder()