From e50e1d9bd0eb39eab74460665ce4be08b4fc00b8 Mon Sep 17 00:00:00 2001
From: cmdlineluser <99486669+cmdlineluser@users.noreply.github.com>
Date: Thu, 27 Jul 2023 12:40:15 +0100
Subject: [PATCH] fix(rust, python): Fix struct get field by index out of
 bounds error. (#10097)

---
 .../polars-plan/src/dsl/function_expr/schema.rs      | 12 +++++++++---
 py-polars/tests/unit/datatypes/test_struct.py        |  6 ++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/polars/polars-lazy/polars-plan/src/dsl/function_expr/schema.rs b/polars/polars-lazy/polars-plan/src/dsl/function_expr/schema.rs
index 4cb56d8a575a..82dd321fd853 100644
--- a/polars/polars-lazy/polars-plan/src/dsl/function_expr/schema.rs
+++ b/polars/polars-lazy/polars-plan/src/dsl/function_expr/schema.rs
@@ -177,9 +177,15 @@ impl FunctionExpr {
                 match s {
                     FieldByIndex(index) => {
                         let (index, _) = slice_offsets(*index, 0, fields.len());
-                        fields.get(index).cloned().ok_or_else(
-                            || polars_err!(ComputeError: "index out of bounds in `struct.field`"),
-                        )
+                        if let DataType::Struct(flds) = &fields[0].dtype {
+                            flds.get(index).cloned().ok_or_else(
+                                || polars_err!(ComputeError: "index out of bounds in `struct.field`")
+                            )
+                        } else {
+                            polars_bail!(
+                                ComputeError: "expected struct dtype, got: `{}`", &fields[0].dtype
+                            )
+                        }
                     }
                     FieldByName(name) => {
                         if let DataType::Struct(flds) = &fields[0].dtype {
diff --git a/py-polars/tests/unit/datatypes/test_struct.py b/py-polars/tests/unit/datatypes/test_struct.py
index 72e9316448d5..1fc7bf5b27b2 100644
--- a/py-polars/tests/unit/datatypes/test_struct.py
+++ b/py-polars/tests/unit/datatypes/test_struct.py
@@ -857,3 +857,9 @@ def test_struct_null_count_strict_cast() -> None:
     s = pl.Series([{"a": None}]).cast(pl.Struct({"a": pl.Categorical}))
     assert s.dtype == pl.Struct([pl.Field("a", pl.Categorical)])
     assert s.to_list() == [{"a": None}]
+
+
+def test_struct_get_field_by_index() -> None:
+    df = pl.DataFrame({"val": [{"a": 1, "b": 2}]})
+    expected = {"b": [2]}
+    assert df.select(pl.all().struct[1]).to_dict(as_series=False) == expected