Fix polyval overloads (#7315)

* fix polyval overloads

* add to whatsnew

Author: headtr1ck

doc/whats-new.rst

@@ -57,6 +57,8 @@ Bug fixes
 
 - Import ``nc_time_axis`` when needed (:issue:`7275`, :pull:`7276`).
   By `Michael Niklas <https://github.com/headtr1ck>`_.
+- Fix static typing of :py:meth:`xr.polyval` (:issue:`7312`, :pull:`7315`).
+  By `Michael Niklas <https://github.com/headtr1ck>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/core/computation.py

@@ -1876,22 +1876,30 @@ def where(cond, x, y, keep_attrs=None):
 
 
 @overload
-def polyval(coord: DataArray, coeffs: DataArray, degree_dim: Hashable) -> DataArray:
+def polyval(
+    coord: DataArray, coeffs: DataArray, degree_dim: Hashable = "degree"
+) -> DataArray:
     ...
 
 
 @overload
-def polyval(coord: DataArray, coeffs: Dataset, degree_dim: Hashable) -> Dataset:
+def polyval(
+    coord: DataArray, coeffs: Dataset, degree_dim: Hashable = "degree"
+) -> Dataset:
     ...
 
 
 @overload
-def polyval(coord: Dataset, coeffs: DataArray, degree_dim: Hashable) -> Dataset:
+def polyval(
+    coord: Dataset, coeffs: DataArray, degree_dim: Hashable = "degree"
+) -> Dataset:
     ...
 
 
 @overload
-def polyval(coord: Dataset, coeffs: Dataset, degree_dim: Hashable) -> Dataset:
+def polyval(
+    coord: Dataset, coeffs: Dataset, degree_dim: Hashable = "degree"
+) -> Dataset:
     ...