fix: Type conversion from Spark Struct to narwhals Struct. (#2037)

* Fixed conversion between Spark Struct type to narwhals Struct type.

* Updated test

* Addressed PR comment

Author: osoucy

narwhals/_spark_like/utils.py

@@ -64,12 +64,12 @@ def native_to_narwhals_dtype(
         return dtypes.Struct(
             fields=[
                 dtypes.Field(
-                    name=name,
+                    name=field.name,
                     dtype=native_to_narwhals_dtype(
-                        dtype[name], version=version, spark_types=spark_types
+                        field.dataType, version=version, spark_types=spark_types
                     ),
                 )
-                for name in dtype.fieldNames()
+                for field in dtype
             ]
         )
     return dtypes.Unknown()

tests/expr_and_series/cast_test.py

@@ -260,14 +260,20 @@ def test_cast_struct(request: pytest.FixtureRequest, constructor: Constructor) -
         native_df = native_df.withColumn(  # type: ignore[union-attr]
             "a",
             F.struct(
-                F.col("a.movie ").alias("movie ").cast(T.StringType()),
-                F.col("a.rating").alias("rating").cast(T.DoubleType()),
+                F.col("a.movie ").cast(T.StringType()).alias("movie "),
+                F.col("a.rating").cast(T.DoubleType()).alias("rating"),
             ),
         )
+        assert nw.from_native(native_df).schema == nw.Schema(
+            {
+                "a": nw.Struct(
+                    [nw.Field("movie ", nw.String()), nw.Field("rating", nw.Float64())]
+                )
+            }
+        )
 
-    dtype = nw.Struct([nw.Field("movie ", nw.String()), nw.Field("rating", nw.Float64())])
+    dtype = nw.Struct([nw.Field("movie ", nw.String()), nw.Field("rating", nw.Float32())])
     result = nw.from_native(native_df).select(nw.col("a").cast(dtype)).lazy().collect()
-
     assert result.schema == {"a": dtype}