fix zero column virtual_table handling to check expressions also (#155)

Author: scgkiran

src/from_substrait.cpp

@@ -575,9 +575,13 @@ SubstraitToDuckDB::TransformProjectOp(const substrait::Rel &sop,
 	size_t num_input_columns = 0;
 	if (sop.project().input().rel_type_case() == substrait::Rel::RelTypeCase::kRead) {
 		auto &sget = sop.project().input().read();
-		if (sget.has_virtual_table() && sget.virtual_table().values().empty()) {
-			hasZeroColumnVirtualTable = true;
-			input_rel = GetValueRelationWithSingleBoolColumn();
+		if (sget.has_virtual_table()) {
+			auto virtual_table = sget.virtual_table();
+			if ((virtual_table.values().empty() && virtual_table.expressions().empty()) ||
+			    (virtual_table.expressions().size() > 0 && virtual_table.expressions(0).fields().empty())) {
+				hasZeroColumnVirtualTable = true;
+				input_rel = GetValueRelationWithSingleBoolColumn();
+			}
 		}
 	}
 	if (!hasZeroColumnVirtualTable) {

test/c/test_substrait_c_api.cpp

@@ -658,4 +658,13 @@ TEST_CASE("Test C VirtualTable with bad input Literal", "[substrait-api]") {
 
 	auto json_plan = R"({"version":{"minorNumber":29, "producer":"substrait-go"}, "relations":[{"root":{"input":{"project":{"common":{"direct":{}}, "input":{"read":{"common":{"direct":{}}, "baseSchema":{"struct":{"nullability":"NULLABILITY_REQUIRED"}}, "virtualTable":{"expressions":[{}]}}}, "expressions":[{"literal":{"decimal":{"value":"AQ==", "precision":1}, "nullable":true}}]}}, "names":["?column?"]}}]})";
 	REQUIRE_THROWS(FromSubstraitJSON(con,json_plan));
+}
+
+TEST_CASE("Test C Project with VirtualTable", "[substrait-api]") {
+	DuckDB db(nullptr);
+	Connection con(db);
+
+	auto json_plan = R"({"version":{"minorNumber":29, "producer":"substrait-go darwin/arm64"}, "relations":[{"root":{"input":{"project":{"common":{"emit":{"outputMapping":[2]}}, "input":{"read":{"common":{"direct":{}}, "baseSchema":{"names":["c1", "c2"], "struct":{"types":[{"fp64":{"nullability":"NULLABILITY_NULLABLE"}}, {"fp64":{"nullability":"NULLABILITY_NULLABLE"}}], "nullability":"NULLABILITY_REQUIRED"}}, "virtualTable":{"expressions":[{"fields":[{"literal":{"fp64":1, "nullable":true}}, {"literal":{"fp64":2, "nullable":true}}]}]}}}, "expressions":[{"literal":{"fp64":42}}]}}, "names":["p1"]}}]})";
+	auto result = FromSubstraitJSON(con,json_plan);
+	REQUIRE(CHECK_COLUMN(result, 0, {42}));
 }