Backport PR #7344 on branch 5.1 (Raise our own error when trying to rotate a map of integer data while using a missing value of NaN)

changelog/7344.bugfix.rst

@@ -0,0 +1 @@
+When calling :meth:`sunpy.map.GenericMap.rotate` on an integer data array, with ``missing`` set to NaN (the default value), the method will now itself raise an informative error message instead deferring to NumPy to raise the error.

sunpy/map/mapbase.py

@@ -17,7 +17,6 @@
 import numpy as np
 from matplotlib.backend_bases import FigureCanvasBase
 from matplotlib.figure import Figure
-from packaging import version
 
 try:
     from dask.array import Array as DaskArray
@@ -1701,16 +1700,17 @@ def rotate(self, angle: u.deg = None, rmatrix=None, order=3, scale=1.0,
         unpad_x = -np.min((diff[0], 0))
         unpad_y = -np.min((diff[1], 0))
 
-        # Numpy 1.20+ prevents np.pad from padding with NaNs in integer arrays
-        # Before it would be cast to 0, but now it raises an error.
-        if version.parse(np.__version__) < version.parse("1.20.0") and issubclass(self.data.dtype.type, numbers.Integral) and (missing % 1 != 0):
-            warn_user("The specified `missing` value is not an integer, but the data "
-                      "array is of integer type, so the output may be strange.")
-        # Pad the image array
+        # Raise an informative error message if trying to pad an integer array with NaNs
+        if (pad_x > 0 or pad_y > 0) and issubclass(self.data.dtype.type, numbers.Integral) and (missing % 1 != 0):
+            raise ValueError("The underlying data is integers, but the fill value for missing "
+                             "pixels cannot be cast to an integer, which is the case for the "
+                             "default fill value of NaN.  Set the `missing` keyword to an "
+                             "appropriate integer value for the data set.")
+
         new_data = np.pad(self.data,
-                          ((pad_y, pad_y), (pad_x, pad_x)),
-                          mode='constant',
-                          constant_values=(missing, missing))
+                      ((pad_y, pad_y), (pad_x, pad_x)),
+                      mode='constant',
+                      constant_values=(missing, missing))
 
         # All of the following pixel calculations use a pixel origin of 0
         pixel_array_center = (np.flipud(new_data.shape) - 1) / 2.0

sunpy/map/tests/test_mapbase.py

@@ -11,7 +11,6 @@
 import pytest
 from hypothesis import HealthCheck, given, settings
 from matplotlib.figure import Figure
-from packaging import version
 
 import astropy.units as u
 import astropy.wcs
@@ -1028,30 +1027,15 @@ def test_rotate(aia171_test_map):
     assert aia171_test_map_crop_rot.data.shape[0] < aia171_test_map_crop_rot.data.shape[1]
 
 
-@pytest.mark.xfail(version.parse(np.__version__) >= version.parse("1.20.0"),
-                   reason="Numpy >= 1.20.0 doesn't allow NaN to int conversion")
-def test_rotate_with_incompatible_missing_dtype_warning():
-    data = np.arange(0, 100).reshape(10, 10)
-    coord = SkyCoord(0 * u.arcsec, 0 * u.arcsec, obstime='2013-10-28',
-                     observer='earth', frame=sunpy.coordinates.Helioprojective)
-    header = sunpy.map.make_fitswcs_header(data, coord)
-    test_map = sunpy.map.Map(data, header)
-    with pytest.warns(SunpyUserWarning,
-                      match="The specified `missing` value is not an integer, but the data "
-                      "array is of integer type, so the output may be strange."):
-        test_map.rotate(order=3, missing=np.nan)
-
-
-@pytest.mark.skipif(version.parse(np.__version__) <= version.parse("1.20.0"),
-                    reason="Numpy >= 1.20.0 doesn't allow NaN to int conversion")
 def test_rotate_with_incompatible_missing_dtype_error():
     data = np.arange(0, 100).reshape(10, 10)
     coord = SkyCoord(0 * u.arcsec, 0 * u.arcsec, obstime='2013-10-28',
                      observer='earth', frame=sunpy.coordinates.Helioprojective)
     header = sunpy.map.make_fitswcs_header(data, coord)
     test_map = sunpy.map.Map(data, header)
-    with pytest.raises(ValueError, match="cannot convert float NaN to integer"):
-        test_map.rotate(order=3, missing=np.nan)
+    with pytest.raises(ValueError, match="The underlying data is integers, but the fill value for "
+                                         "missing pixels cannot be cast to an integer"):
+        test_map.rotate(angle=45 * u.deg, missing=np.nan, order=3)
 
 
 def test_rotate_crpix_zero_degrees(generic_map):