Fix concatenating structs (#8811)

Closes #8802. Currently, when struct series are concatenated, the resulting fields are reset, this PR addresses this by reconstructing the fields once the concatenated series is returned.

Authors:
  - https://github.com/shaneding

Approvers:
  - GALI PREM SAGAR (https://github.com/galipremsagar)
  - Charles Blackmon-Luca (https://github.com/charlesbluca)

URL: #8811

python/cudf/cudf/core/series.py

@@ -2433,6 +2433,9 @@ def _concat(cls, objs, axis=0, index=True):
         if isinstance(col, cudf.core.column.Decimal64Column):
             col = col._with_type_metadata(objs[0]._column.dtype)
 
+        if isinstance(col, cudf.core.column.StructColumn):
+            col = col._with_type_metadata(objs[0].dtype)
+
         return cls(data=col, index=index, name=name)
 
     @property

python/cudf/cudf/tests/test_concat.py

@@ -1527,3 +1527,26 @@ def test_concat_decimal_numeric_series(s1, s2, s3, expected):
 def test_concat_decimal_non_numeric(s1, s2, expected):
     s = gd.concat([s1, s2])
     assert_eq(s, expected)
+
+
+@pytest.mark.parametrize(
+    "s1, s2, expected",
+    [
+        (
+            gd.Series([{"a": 5}, {"c": "hello"}, {"b": 7}]),
+            gd.Series([{"a": 5, "c": "hello", "b": 7}]),
+            gd.Series(
+                [
+                    {"a": 5, "b": None, "c": None},
+                    {"a": None, "b": None, "c": "hello"},
+                    {"a": None, "b": 7, "c": None},
+                    {"a": 5, "b": 7, "c": "hello"},
+                ],
+                index=[0, 1, 2, 0],
+            ),
+        )
+    ],
+)
+def test_concat_struct_column(s1, s2, expected):
+    s = gd.concat([s1, s2])
+    assert_eq(s, expected)