BUG: move nan-handling to tslib

Author: AlexKirko

pandas/_libs/tslib.pyx

@@ -296,8 +296,8 @@ def format_array_from_datetime(ndarray[int64_t] values, object tz=None,
     return result
 
 
-def array_with_unit_to_datetime(ndarray values, object unit,
-                                str errors='coerce'):
+def array_with_unit_to_datetime(ndarray values, object unit, 
+                                str errors='coerce', ndarray mask=None):
     """
     convert the ndarray according to the unit
     if errors:
@@ -316,7 +316,6 @@ def array_with_unit_to_datetime(ndarray values, object unit,
         Py_ssize_t i, j, n=len(values)
         int64_t m
         ndarray[float64_t] fvalues
-        ndarray mask
         bint is_ignore = errors=='ignore'
         bint is_coerce = errors=='coerce'
         bint is_raise = errors=='raise'
@@ -329,9 +328,13 @@ def array_with_unit_to_datetime(ndarray values, object unit,
 
     if unit == 'ns':
         if issubclass(values.dtype.type, np.integer):
-            return values.astype('M8[ns]'), tz
-        # This will return a tz
-        return array_to_datetime(values.astype(object), errors=errors)
+            result = values.astype('M8[ns]')
+        else:
+            result, tz = array_to_datetime(values.astype(object), errors=errors)
+        if mask is not None:
+            iresult = result.view('i8')
+            iresult[mask] = NPY_NAT
+        return result, tz
 
     m = cast_from_unit(None, unit)
 
@@ -343,7 +346,9 @@ def array_with_unit_to_datetime(ndarray values, object unit,
         if values.dtype.kind == "i":
             # Note: this condition makes the casting="same_kind" redundant
             iresult = values.astype('i8', casting='same_kind', copy=False)
-            mask = iresult == NPY_NAT
+            # If no mask, fill mask by comparing to NPY_NAT constant
+            if mask is None:
+                mask = iresult == NPY_NAT
             iresult[mask] = 0
             fvalues = iresult.astype('f8') * m
             need_to_iterate = False

pandas/core/tools/datetimes.py

@@ -321,15 +321,12 @@ def _convert_listlike_datetimes(
         # GH 30050 pass an ndarray to tslib.array_with_unit_to_datetime
         # because it expects an ndarray argument
         if isinstance(arg, IntegerArray):
-            # Send only non-na values to array_with_unit_to_datetime
+            # Explicitly pass NaT mask to array_with_unit_to_datetime
             mask_na = arg.isna()
+            arg = getattr(arg, "_ndarray_values", arg)
             result, tz_parsed = tslib.array_with_unit_to_datetime(
-                np.compress(np.logical_not(mask_na), arg), unit, errors=errors
+                arg, unit, mask=mask_na, errors=errors
             )
-            # Insert na values back in proper positions
-            ins_index = np.ravel(np.argwhere(mask_na))
-            ins_index -= range(ins_index.shape[0])
-            result = np.insert(result, ins_index, None)
         else:
             result, tz_parsed = tslib.array_with_unit_to_datetime(
                 arg, unit, errors=errors