From c72a1c4a4c52152bdab83f60f35615de28e8be7f Mon Sep 17 00:00:00 2001
From: Tom White <tom.e.white@gmail.com>
Date: Tue, 28 Jun 2022 10:38:47 +0100
Subject: [PATCH] Support NumPy array API (experimental)

---
 xarray/core/duck_array_ops.py |  6 ++++-
 xarray/core/indexing.py       | 42 +++++++++++++++++++++++++++++++++++
 xarray/core/utils.py          |  5 +++--
 xarray/core/variable.py       |  4 +++-
 4 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/xarray/core/duck_array_ops.py b/xarray/core/duck_array_ops.py
index 6e73ee41b40..2cd2fb3af04 100644
--- a/xarray/core/duck_array_ops.py
+++ b/xarray/core/duck_array_ops.py
@@ -329,7 +329,11 @@ def f(values, axis=None, skipna=None, **kwargs):
             if name in ["sum", "prod"]:
                 kwargs.pop("min_count", None)
 
-            func = getattr(np, name)
+            if hasattr(values, "__array_namespace__"):
+                xp = values.__array_namespace__()
+                func = getattr(xp, name)
+            else:
+                func = getattr(np, name)
 
         try:
             with warnings.catch_warnings():
diff --git a/xarray/core/indexing.py b/xarray/core/indexing.py
index cbbd507eeff..008532fd449 100644
--- a/xarray/core/indexing.py
+++ b/xarray/core/indexing.py
@@ -672,6 +672,8 @@ def as_indexable(array):
         return DaskIndexingAdapter(array)
     if hasattr(array, "__array_function__"):
         return NdArrayLikeIndexingAdapter(array)
+    if hasattr(array, "__array_namespace__"):
+        return ArrayApiIndexingAdapter(array)
 
     raise TypeError(f"Invalid array type: {type(array)}")
 
@@ -1281,6 +1283,46 @@ def __init__(self, array):
         self.array = array
 
 
+class ArrayApiIndexingAdapter(ExplicitlyIndexedNDArrayMixin):
+    """Wrap an array API array to use explicit indexing."""
+    __slots__ = ("array",)
+
+    def __init__(self, array):
+        if not hasattr(array, "__array_namespace__"):
+            raise TypeError(
+                "ArrayApiIndexingAdapter must wrap an object that "
+                "implements the __array_namespace__ protocol"
+            )
+        self.array = array
+
+    def __getitem__(self, key):
+        if isinstance(key, BasicIndexer):
+            return self.array[key.tuple]
+        elif isinstance(key, OuterIndexer):
+            # manual orthogonal indexing (implemented like DaskIndexingAdapter) 
+            key = key.tuple
+            value = self.array
+            for axis, subkey in reversed(list(enumerate(key))):
+                value = value[(slice(None),) * axis + (subkey, Ellipsis)]
+            return value
+        else:
+            assert isinstance(key, VectorizedIndexer)
+            raise TypeError("Vectorized indexing is not supported")
+
+    def __setitem__(self, key, value):
+        if isinstance(key, BasicIndexer):
+            self.array[key.tuple] = value
+        elif isinstance(key, OuterIndexer):
+            self.array[key.tuple] = value
+        else:
+            assert isinstance(key, VectorizedIndexer)
+            raise TypeError("Vectorized indexing is not supported")
+
+    def transpose(self, order):
+        xp = self.array.__array_namespace__()
+        return xp.permute_dims(self.array, order)
+
+
 class DaskIndexingAdapter(ExplicitlyIndexedNDArrayMixin):
     """Wrap a dask array to support explicit indexing."""
 
diff --git a/xarray/core/utils.py b/xarray/core/utils.py
index b253f1661ae..4be532d6bcf 100644
--- a/xarray/core/utils.py
+++ b/xarray/core/utils.py
@@ -262,8 +262,8 @@ def is_duck_array(value: Any) -> bool:
         hasattr(value, "ndim")
         and hasattr(value, "shape")
         and hasattr(value, "dtype")
-        and hasattr(value, "__array_function__")
-        and hasattr(value, "__array_ufunc__")
+        and ((hasattr(value, "__array_function__") and hasattr(value, "__array_ufunc__"))
+            or hasattr(value, "__array_namespace__"))
     )
 
 
@@ -297,6 +297,7 @@ def _is_scalar(value, include_0d):
         or not (
             isinstance(value, (Iterable,) + NON_NUMPY_SUPPORTED_ARRAY_TYPES)
             or hasattr(value, "__array_function__")
+            or hasattr(value, "__array_namespace__")
         )
     )
 
diff --git a/xarray/core/variable.py b/xarray/core/variable.py
index 2d115ff0ed9..baeae480e81 100644
--- a/xarray/core/variable.py
+++ b/xarray/core/variable.py
@@ -201,7 +201,9 @@ def as_compatible_data(data, fastpath=False):
     if isinstance(data, (Variable, DataArray)):
         return data.data
 
-    if isinstance(data, NON_NUMPY_SUPPORTED_ARRAY_TYPES):
+    if (isinstance(data, NON_NUMPY_SUPPORTED_ARRAY_TYPES)
+        or hasattr(data, "__array_function__")
+        or hasattr(data, "__array_namespace__")):
         return _maybe_wrap_data(data)
 
     if isinstance(data, tuple):