backwards compat for equals (#326)

* backwards-compat for indexes without `exclude`

* comments and a marker about the deprecation

Author: keewis

pint_xarray/index.py

@@ -1,3 +1,5 @@
+import inspect
+
 from xarray import Variable
 from xarray.core.indexes import Index, PandasIndex
 
@@ -80,14 +82,31 @@ def equals(self, other, *, exclude=None):
         if not isinstance(other, PintIndex):
             return False
 
-        # for now we require exactly matching units to avoid the potentially expensive conversion
+        # for now we require exactly matching units to avoid the potentially
+        # expensive conversion
         if self.units != other.units:
             return False
 
-        # Explicitly pass `exclude`, the index does not officially support
-        # indexes other than the PandasIndex
+        # TODO:
+        # - remove try-except once we can drop xarray<2025.06.0
+        # - remove compat once we can require a version of xarray that completed
+        #   the deprecation cycle
+        try:
+            from xarray.core.indexes import _wrap_index_equals
+
+            equals = _wrap_index_equals(self.index)
+            kwargs = {"exclude": exclude}
+        except ImportError:  # pragma: no cover
+            equals = self.index.equals
+            signature = inspect.signature(self.index.equals)
+
+            if "exclude" in signature.parameters:
+                kwargs = {"exclude": exclude}
+            else:
+                kwargs = {}
+
         # Last to avoid the potentially expensive comparison
-        return self.index.equals(other.index, exclude=exclude)
+        return equals(other.index, **kwargs)
 
     def roll(self, shifts):
         return self._replace(self.index.roll(shifts))