Revert some old pieces of DeviceScalar._set_dtype

python/cudf/cudf/_lib/scalar.pyx

@@ -13,16 +13,18 @@ from libcpp.utility cimport move
 import pylibcudf as plc
 
 import cudf
-from cudf._lib.types import dtype_from_pylibcudf_column
+from cudf.core.dtypes import ListDtype, StructDtype
+from cudf._lib.types import PYLIBCUDF_TO_SUPPORTED_NUMPY_TYPES
+from cudf._lib.types cimport dtype_from_column_view, underlying_type_t_type_id
 from cudf.core.missing import NA, NaT
 
 # We currently need this cimport because some of the implementations here
 # access the c_obj of the scalar, and because we need to be able to call
 # pylibcudf.Scalar.from_libcudf. Both of those are temporarily acceptable until
 # DeviceScalar is phased out entirely from cuDF Cython (at which point
 # cudf.Scalar will be directly backed by pylibcudf.Scalar).
-from pylibcudf cimport Scalar as plc_Scalar
-from pylibcudf.libcudf.scalar.scalar cimport scalar
+from pylibcudf cimport Scalar as plc_Scalar, type_id as plc_TypeID
+from pylibcudf.libcudf.scalar.scalar cimport list_scalar, scalar, struct_scalar
 
 
 def _replace_nested(obj, check, replacement):
@@ -221,19 +223,43 @@ cdef class DeviceScalar:
         return s
 
     cdef void _set_dtype(self, dtype=None):
+        cdef plc_TypeID cdtype_id = self.c_value.type().id()
         if dtype is not None:
             self._dtype = dtype
-
-        plc_scalar = self.c_value
-        if plc_scalar.type().id() in {
-            plc.TypeId.DECIMAL32,
-            plc.TypeId.DECIMAL64,
-            plc.TypeId.DECIMAL128,
+        elif cdtype_id in {
+            plc_TypeID.DECIMAL32,
+            plc_TypeID.DECIMAL64,
+            plc_TypeID.DECIMAL128,
         }:
             raise TypeError(
                 "Must pass a dtype when constructing from a fixed-point scalar"
             )
-        self._dtype = dtype_from_pylibcudf_column(plc.Column.from_scalar(plc_scalar, 1))
+        elif cdtype_id == plc_TypeID.STRUCT:
+            struct_table_view = (<struct_scalar*>self.get_raw_ptr())[0].view()
+            self._dtype = StructDtype({
+                str(i): dtype_from_column_view(struct_table_view.column(i))
+                for i in range(struct_table_view.num_columns())
+            })
+        elif cdtype_id == plc_TypeID.LIST:
+            if (
+                <list_scalar*>self.get_raw_ptr()
+            )[0].view().type().id() == plc_TypeID.LIST:
+                self._dtype = dtype_from_column_view(
+                    (<list_scalar*>self.get_raw_ptr())[0].view()
+                )
+            else:
+                self._dtype = ListDtype(
+                    PYLIBCUDF_TO_SUPPORTED_NUMPY_TYPES[
+                        <underlying_type_t_type_id>(
+                            (<list_scalar*>self.get_raw_ptr())[0]
+                            .view().type().id()
+                        )
+                    ]
+                )
+        else:
+            self._dtype = PYLIBCUDF_TO_SUPPORTED_NUMPY_TYPES[
+                <underlying_type_t_type_id>(cdtype_id)
+            ]
 
 
 def as_device_scalar(val, dtype=None):