feat: Handle empty child values for list constants (#186)

Co-authored-by: Kirill Müller <[email protected]>

Author: romainfrancois

src/utils.cpp

@@ -233,6 +233,9 @@ Value RApiTypes::SexpToValue(SEXP valsexp, R_len_t idx, bool typed_logical_null)
 			auto value = SexpToValue(ts_val, child_idx);
 			child_values.push_back(value);
 		}
+		if (child_values.empty()) {
+			return Value::EMPTYLIST(RApiTypes::LogicalTypeFromRType(child_rtype, true));
+		}
 		return Value::LIST(std::move(child_values));
 	}
 	case RTypeId::STRUCT: {

tests/testthat/_snaps/relational.md

@@ -64,3 +64,10 @@
       Error:
       ! expr_comparison: Invalid comparison operator
 
+# Handle zero-length lists (#186)
+
+    Code
+      expr_constant(list(integer()))
+    Message
+      DuckDB Expression: []
+

tests/testthat/test-relational.R

@@ -897,3 +897,11 @@ test_that("we don't crash with evaluation errors", {
   # If this succeeds, find a new query that throws a runtime error.
   expect_error(nrow(ans), "Error evaluating duckdb query")
 })
+
+test_that("Handle zero-length lists (#186)", {
+  local_edition(3)
+
+  expect_snapshot({
+    expr_constant(list(integer()))
+  })
+})