effectively remove fastpath

xarray/core/indexes.py

@@ -580,19 +580,10 @@ def __init__(
         array: Any,
         dim: Hashable,
         coord_dtype: Any = None,
-        *,
-        fastpath: bool = False,
     ):
-        if fastpath:
-            index = array
-        else:
-            index = safe_cast_to_index(array)
+        index = safe_cast_to_index(array).copy()
 
         if index.name is None:
-            # make a shallow copy: cheap and because the index name may be updated
-            # here or in other constructors (cannot use pd.Index.rename as this
-            # constructor is also called from PandasMultiIndex)
-            index = index.copy()
             index.name = dim
 
         self.index = index
@@ -607,7 +598,7 @@ def _replace(self, index, dim=None, coord_dtype=None):
             dim = self.dim
         if coord_dtype is None:
             coord_dtype = self.coord_dtype
-        return type(self)(index, dim, coord_dtype, fastpath=True)
+        return type(self)(index, dim, coord_dtype)
 
     @classmethod
     def from_variables(
@@ -653,11 +644,6 @@ def from_variables(
 
         obj = cls(data, dim, coord_dtype=var.dtype)
         assert not isinstance(obj.index, pd.MultiIndex)
-        # Rename safely
-        # make a shallow copy: cheap and because the index name may be updated
-        # here or in other constructors (cannot use pd.Index.rename as this
-        # constructor is also called from PandasMultiIndex)
-        obj.index = obj.index.copy()
         obj.index.name = name
 
         return obj