Disable export for unsupported units (spacetelescope#2784)

CHANGES.rst

@@ -16,7 +16,7 @@ New Features
 - "Export Plot" plugin is now replaced with the more general "Export" plugin. [#2722, #2782]
 
 - "Export" plugin supports exporting plugin tables, plugin plots, data, and
-  non-composite spatial subsets.[#2755, #2774, #2760, #2772, #2770, #2780]
+  non-composite spatial subsets.[#2755, #2774, #2760, #2772, #2770, #2780, #2784]
 
 - Opening a plugin in the tray (from the API or the toolbar buttons) now scrolls to that plugin.
   [#2768]

jdaviz/configs/default/plugins/export/export.py

@@ -16,6 +16,7 @@
 from jdaviz.core.events import AddDataMessage, SnackbarMessage
 from jdaviz.core.user_api import PluginUserApi
 from specutils import Spectrum1D
+from astropy import units as u
 from astropy.nddata import CCDData
 
 try:
@@ -257,6 +258,8 @@ def _set_dataset_not_supported_msg(self, msg=None):
                 self.data_invalid_msg = "Data export is only available for plugin generated data."
             elif not isinstance(self.dataset.selected_obj, (Spectrum1D, CCDData)):
                 self.data_invalid_msg = "Export is not yet implemented for this type of data"
+            elif (data_unit := self.dataset.selected_obj.unit) == u.Unit('DN/s'):
+                self.data_invalid_msg = f'Export Disabled: The unit {data_unit} could not be saved in native FITS format.'  # noqa: E501
             else:
                 self.data_invalid_msg = ''
         else:

jdaviz/configs/default/plugins/export/tests/test_export.py

@@ -204,6 +204,26 @@ def test_export_data(cubeviz_helper, spectrum1d_cube):
     assert ep.data_invalid_msg == ''
 
 
+def test_disable_export_for_unsupported_units(specviz2d_helper):
+    dn_per_s = u.DN / u.s
+    data = np.zeros((5, 10))
+    data[3] = np.arange(10)
+    data = Spectrum1D(flux=data*dn_per_s, spectral_axis=data[3]*u.um)
+    specviz2d_helper.load_data(data)
+
+    gs = specviz2d_helper.plugins["Gaussian Smooth"]
+    smooth_source_dataset = "Spectrum 1D"
+    gs.dataset = smooth_source_dataset
+    gs.stddev = 3
+    gs.smooth(add_data=True)
+
+    ep = specviz2d_helper.plugins["Export"]._obj
+    assert "Spectrum 1D smooth stddev-3.0" in ep.dataset.choices
+    ep.dataset_selected = "Spectrum 1D smooth stddev-3.0"
+    assert ep.dataset.selected_obj.unit == "DN/s"
+    assert ep.data_invalid_msg == "Export Disabled: The unit DN / s could not be saved in native FITS format."  # noqa
+
+
 class TestExportPluginPlots():
 
     def test_basic_export_plugin_plots(tmp_path, imviz_helper):