improve the error message for invalid hue names (#5060)

Author: keewis

xarray/plot/plot.py

@@ -65,6 +65,8 @@ def _infer_line_data(darray, x, y, hue):
             raise ValueError("For 2D inputs, please specify either hue, x or y.")
 
         if y is None:
+            if hue is not None:
+                _assert_valid_xy(darray, hue, "hue")
             xname, huename = _infer_xy_labels(darray=darray, x=x, y=hue)
             xplt = darray[xname]
             if xplt.ndim > 1:

xarray/tests/test_plot.py

@@ -267,6 +267,15 @@ def test_line_plot_along_1d_coord(self):
         line = da.plot(y="time", hue="x")[0]
         assert_array_equal(line.get_ydata(), da.coords["time"].values)
 
+    def test_line_plot_wrong_hue(self):
+        da = xr.DataArray(
+            data=np.array([[0, 1], [5, 9]]),
+            dims=["x", "t"],
+        )
+
+        with pytest.raises(ValueError, match="hue must be one of"):
+            da.plot(x="t", hue="wrong_coord")
+
     def test_2d_line(self):
         with raises_regex(ValueError, "hue"):
             self.darray[:, :, 0].plot.line()