From e8f539a231db9ba240bc91c41a4afcb1810f6d32 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Mon, 20 Jan 2020 13:52:11 +0100
Subject: [PATCH 01/16] API: generalized check_array_indexer for validating
 array-like indexers

---
 pandas/api/indexers/__init__.py         |  4 +-
 pandas/core/arrays/categorical.py       | 11 ++---
 pandas/core/arrays/datetimelike.py      |  6 ++-
 pandas/core/arrays/interval.py          |  3 ++
 pandas/core/arrays/masked.py            | 14 ++++--
 pandas/core/arrays/numpy_.py            |  8 +--
 pandas/core/arrays/sparse/array.py      |  5 ++
 pandas/core/indexers.py                 | 66 ++++++++++++++++++++++++-
 pandas/tests/extension/base/getitem.py  | 32 ++++++++++++
 pandas/tests/extension/decimal/array.py |  8 +--
 pandas/tests/extension/json/array.py    |  7 +--
 11 files changed, 131 insertions(+), 33 deletions(-)

diff --git a/pandas/api/indexers/__init__.py b/pandas/api/indexers/__init__.py
index 10654eb0888ee..e0050326e791a 100644
--- a/pandas/api/indexers/__init__.py
+++ b/pandas/api/indexers/__init__.py
@@ -2,7 +2,7 @@
 Public API for Rolling Window Indexers.
 """
 
-from pandas.core.indexers import check_bool_array_indexer
+from pandas.core.indexers import check_array_indexer, check_bool_array_indexer
 from pandas.core.window.indexers import BaseIndexer
 
-__all__ = ["check_bool_array_indexer", "BaseIndexer"]
+__all__ = ["check_array_indexer", "check_bool_array_indexer", "BaseIndexer"]
diff --git a/pandas/core/arrays/categorical.py b/pandas/core/arrays/categorical.py
index 9d7359dd9c614..3c717458797b5 100644
--- a/pandas/core/arrays/categorical.py
+++ b/pandas/core/arrays/categorical.py
@@ -39,7 +39,7 @@
 )
 from pandas.core.dtypes.dtypes import CategoricalDtype
 from pandas.core.dtypes.generic import ABCIndexClass, ABCSeries
-from pandas.core.dtypes.inference import is_array_like, is_hashable
+from pandas.core.dtypes.inference import is_hashable
 from pandas.core.dtypes.missing import isna, notna
 
 from pandas.core import ops
@@ -54,7 +54,7 @@
 from pandas.core.base import NoNewAttributesMixin, PandasObject, _shared_docs
 import pandas.core.common as com
 from pandas.core.construction import array, extract_array, sanitize_array
-from pandas.core.indexers import check_bool_array_indexer
+from pandas.core.indexers import check_array_indexer
 from pandas.core.missing import interpolate_2d
 from pandas.core.ops.common import unpack_zerodim_and_defer
 from pandas.core.sorting import nargsort
@@ -2001,11 +2001,8 @@ def __getitem__(self, key):
             else:
                 return self.categories[i]
 
-        if is_list_like(key) and not is_array_like(key):
-            key = np.asarray(key)
-
-        if com.is_bool_indexer(key):
-            key = check_bool_array_indexer(self, key)
+        if is_list_like(key):
+            key = check_array_indexer(self, key)
 
         result = self._codes[key]
         if result.ndim > 1:
diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index 70637026c278d..7fb3d31f34e8e 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -42,7 +42,7 @@
 from pandas.core.algorithms import checked_add_with_arr, take, unique1d, value_counts
 from pandas.core.arrays.base import ExtensionArray, ExtensionOpsMixin
 import pandas.core.common as com
-from pandas.core.indexers import check_bool_array_indexer
+from pandas.core.indexers import check_array_indexer
 from pandas.core.ops.common import unpack_zerodim_and_defer
 from pandas.core.ops.invalid import invalid_comparison, make_invalid_op
 
@@ -517,8 +517,10 @@ def __getitem__(self, key):
                 return self._box_func(val)
             return type(self)(val, dtype=self.dtype)
 
+        if is_list_like(key):
+            key = check_array_indexer(self, key)
+
         if com.is_bool_indexer(key):
-            key = check_bool_array_indexer(self, key)
             if key.all():
                 key = slice(0, None, None)
             else:
diff --git a/pandas/core/arrays/interval.py b/pandas/core/arrays/interval.py
index 37d2baed2c09e..23f2151bb593a 100644
--- a/pandas/core/arrays/interval.py
+++ b/pandas/core/arrays/interval.py
@@ -40,6 +40,7 @@
 from pandas.core.arrays.categorical import Categorical
 import pandas.core.common as com
 from pandas.core.construction import array
+from pandas.core.indexers import check_array_indexer
 from pandas.core.indexes.base import ensure_index
 
 _VALID_CLOSED = {"left", "right", "both", "neither"}
@@ -495,6 +496,8 @@ def __len__(self) -> int:
         return len(self.left)
 
     def __getitem__(self, value):
+        if is_list_like(value):
+            value = check_array_indexer(self, value)
         left = self.left[value]
         right = self.right[value]
 
diff --git a/pandas/core/arrays/masked.py b/pandas/core/arrays/masked.py
index 47605413ff1a6..50beb58d79b0e 100644
--- a/pandas/core/arrays/masked.py
+++ b/pandas/core/arrays/masked.py
@@ -4,13 +4,17 @@
 
 from pandas._libs import lib, missing as libmissing
 
-from pandas.core.dtypes.common import is_integer, is_object_dtype, is_string_dtype
+from pandas.core.dtypes.common import (
+    is_integer,
+    is_list_like,
+    is_object_dtype,
+    is_string_dtype,
+)
 from pandas.core.dtypes.missing import isna, notna
 
 from pandas.core.algorithms import take
 from pandas.core.arrays import ExtensionArray, ExtensionOpsMixin
-import pandas.core.common as com
-from pandas.core.indexers import check_bool_array_indexer
+from pandas.core.indexers import check_array_indexer
 
 if TYPE_CHECKING:
     from pandas._typing import Scalar
@@ -35,8 +39,8 @@ def __getitem__(self, item):
                 return self.dtype.na_value
             return self._data[item]
 
-        elif com.is_bool_indexer(item):
-            item = check_bool_array_indexer(self, item)
+        elif is_list_like(item):
+            item = check_array_indexer(self, item)
 
         return type(self)(self._data[item], self._mask[item])
 
diff --git a/pandas/core/arrays/numpy_.py b/pandas/core/arrays/numpy_.py
index 4db3d3010adaf..903b4ad851907 100644
--- a/pandas/core/arrays/numpy_.py
+++ b/pandas/core/arrays/numpy_.py
@@ -9,6 +9,7 @@
 from pandas.util._decorators import Appender
 from pandas.util._validators import validate_fillna_kwargs
 
+from pandas.core.dtypes.common import is_list_like
 from pandas.core.dtypes.dtypes import ExtensionDtype
 from pandas.core.dtypes.generic import ABCIndexClass, ABCSeries
 from pandas.core.dtypes.inference import is_array_like
@@ -18,9 +19,8 @@
 from pandas.core import nanops
 from pandas.core.algorithms import searchsorted, take, unique
 from pandas.core.arrays.base import ExtensionArray, ExtensionOpsMixin
-import pandas.core.common as com
 from pandas.core.construction import extract_array
-from pandas.core.indexers import check_bool_array_indexer
+from pandas.core.indexers import check_array_indexer
 from pandas.core.missing import backfill_1d, pad_1d
 
 
@@ -235,8 +235,8 @@ def __getitem__(self, item):
         if isinstance(item, type(self)):
             item = item._ndarray
 
-        elif com.is_bool_indexer(item):
-            item = check_bool_array_indexer(self, item)
+        elif is_list_like(item):
+            item = check_array_indexer(self, item)
 
         result = self._ndarray[item]
         if not lib.is_scalar(item):
diff --git a/pandas/core/arrays/sparse/array.py b/pandas/core/arrays/sparse/array.py
index e2562a375515d..0f21e4e03b8d2 100644
--- a/pandas/core/arrays/sparse/array.py
+++ b/pandas/core/arrays/sparse/array.py
@@ -29,6 +29,7 @@
     is_datetime64_any_dtype,
     is_dtype_equal,
     is_integer,
+    is_list_like,
     is_object_dtype,
     is_scalar,
     is_string_dtype,
@@ -43,6 +44,7 @@
 from pandas.core.base import PandasObject
 import pandas.core.common as com
 from pandas.core.construction import sanitize_array
+from pandas.core.indexers import check_array_indexer
 from pandas.core.missing import interpolate_2d
 import pandas.core.ops as ops
 from pandas.core.ops.common import unpack_zerodim_and_defer
@@ -768,6 +770,9 @@ def __getitem__(self, key):
                 else:
                     key = np.asarray(key)
 
+            if is_list_like(key):
+                key = check_array_indexer(self, key)
+
             if com.is_bool_indexer(key):
                 key = check_bool_indexer(self, key)
 
diff --git a/pandas/core/indexers.py b/pandas/core/indexers.py
index 4d45769d2fea9..c59f6536683b3 100644
--- a/pandas/core/indexers.py
+++ b/pandas/core/indexers.py
@@ -5,7 +5,12 @@
 
 from pandas._typing import AnyArrayLike
 
-from pandas.core.dtypes.common import is_list_like
+from pandas.core.dtypes.common import (
+    is_array_like,
+    is_bool_dtype,
+    is_integer_dtype,
+    is_list_like,
+)
 from pandas.core.dtypes.generic import ABCIndexClass, ABCSeries
 
 # -----------------------------------------------------------
@@ -307,3 +312,62 @@ def check_bool_array_indexer(array: AnyArrayLike, mask: AnyArrayLike) -> np.ndar
     if len(result) != len(array):
         raise IndexError(f"Item wrong length {len(result)} instead of {len(array)}.")
     return result
+
+
+def check_array_indexer(array, indexer) -> np.ndarray:
+    """
+    Check if `indexer` is a valid array indexer for `array`.
+
+    `array` and `indexer` are checked to have the same length, and the
+    dtype is validated. If it is an integer or boolean ExtensionArray, it is
+    checked if there are missing values present, and it is converted to
+    the appropriate numpy array.
+
+    .. versionadded:: 1.0.0
+
+    Parameters
+    ----------
+    array : array
+        The array that's being indexed (only used for the length).
+    indexer : array-like
+        The array-like that's used to index.
+
+    Returns
+    -------
+    numpy.ndarray
+        The validated indexer.
+
+    Raises
+    ------
+    IndexError
+        When the lengths don't match.
+    ValueError
+        When `indexer` cannot be converted to a numpy ndarray.
+
+    """
+    import pandas as pd
+
+    if not is_array_like(indexer):
+        indexer = pd.array(indexer)
+    dtype = indexer.dtype
+    if is_bool_dtype(dtype):
+        try:
+            indexer = np.asarray(indexer, dtype=bool)
+        except ValueError:
+            raise ValueError("Cannot mask with a boolean indexer containing NA values")
+
+        # GH26658
+        if len(indexer) != len(array):
+            raise IndexError(
+                f"Item wrong length {len(indexer)} instead of {len(array)}."
+            )
+
+    elif is_integer_dtype(dtype):
+        try:
+            indexer = np.asarray(indexer, dtype=int)
+        except ValueError:
+            raise ValueError(
+                "Cannot index with an integer indexer containing NA values"
+            )
+
+    return indexer
diff --git a/pandas/tests/extension/base/getitem.py b/pandas/tests/extension/base/getitem.py
index dc1f62c4c97c5..5c31d6f04335e 100644
--- a/pandas/tests/extension/base/getitem.py
+++ b/pandas/tests/extension/base/getitem.py
@@ -160,6 +160,38 @@ def test_getitem_boolean_array_mask_raises(self, data):
         with pytest.raises(ValueError):
             s[mask]
 
+    @pytest.mark.parametrize(
+        "idx",
+        [[0, 1, 2], pd.array([0, 1, 2], dtype="Int64"), np.array([0, 1, 2])],
+        ids=["list", "integer-array", "numpy-array"],
+    )
+    def test_getitem_integer_array(self, data, idx):
+        result = data[idx]
+        assert len(result) == 3
+        assert isinstance(result, type(data))
+        expected = data.take([0, 1, 2])
+        self.assert_extension_array_equal(result, expected)
+
+        expected = pd.Series(expected)
+        result = pd.Series(data)[idx]
+        self.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize(
+        "idx",
+        [[0, 1, 2, pd.NA], pd.array([0, 1, 2, pd.NA], dtype="Int64")],
+        ids=["list", "integer-array"],
+    )
+    def test_getitem_integer_with_missing_raises(self, data, idx):
+        msg = "Cannot index with an integer indexer containing NA values"
+        with pytest.raises(ValueError, match=msg):
+            data[idx]
+
+        # TODO this raises KeyError about labels not found (it tries label-based)
+        # import pandas._testing as tm
+        # s = pd.Series(data, index=[tm.rands(4) for _ in range(len(data))])
+        # with pytest.raises(ValueError, match=msg):
+        #    s[idx]
+
     def test_getitem_slice(self, data):
         # getitem[slice] should return an array
         result = data[slice(0)]  # empty
diff --git a/pandas/tests/extension/decimal/array.py b/pandas/tests/extension/decimal/array.py
index 85bd5f7a33fe1..12a906b5afbe1 100644
--- a/pandas/tests/extension/decimal/array.py
+++ b/pandas/tests/extension/decimal/array.py
@@ -117,13 +117,7 @@ def __getitem__(self, item):
         else:
             # array, slice.
             if pd.api.types.is_list_like(item):
-                if not pd.api.types.is_array_like(item):
-                    item = pd.array(item)
-                dtype = item.dtype
-                if pd.api.types.is_bool_dtype(dtype):
-                    item = pd.api.indexers.check_bool_array_indexer(self, item)
-                elif pd.api.types.is_integer_dtype(dtype):
-                    item = np.asarray(item, dtype="int")
+                item = pd.api.indexers.check_array_indexer(self, item)
             return type(self)(self._data[item])
 
     def take(self, indexer, allow_fill=False, fill_value=None):
diff --git a/pandas/tests/extension/json/array.py b/pandas/tests/extension/json/array.py
index 17bc2773aad19..fe83200152794 100644
--- a/pandas/tests/extension/json/array.py
+++ b/pandas/tests/extension/json/array.py
@@ -82,11 +82,8 @@ def __getitem__(self, item):
             # slice
             return type(self)(self.data[item])
         else:
-            if not pd.api.types.is_array_like(item):
-                item = pd.array(item)
-            dtype = item.dtype
-            if pd.api.types.is_bool_dtype(dtype):
-                item = pd.api.indexers.check_bool_array_indexer(self, item)
+            item = pd.api.indexers.check_array_indexer(self, item)
+            if pd.api.types.is_bool_dtype(item.dtype):
                 return self._from_sequence([x for x, m in zip(self, item) if m])
             # integer
             return type(self)([self.data[i] for i in item])

From 4fa9f5a79d93ca0a2dabdb6e06d7d340d4003790 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Mon, 20 Jan 2020 14:04:00 +0100
Subject: [PATCH 02/16] test boolean message as well

---
 pandas/tests/extension/base/getitem.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/pandas/tests/extension/base/getitem.py b/pandas/tests/extension/base/getitem.py
index 5c31d6f04335e..337c5bf93ab72 100644
--- a/pandas/tests/extension/base/getitem.py
+++ b/pandas/tests/extension/base/getitem.py
@@ -152,7 +152,9 @@ def test_getitem_boolean_array_mask(self, data):
     def test_getitem_boolean_array_mask_raises(self, data):
         mask = pd.array(np.zeros(data.shape, dtype="bool"), dtype="boolean")
         mask[:2] = pd.NA
-        with pytest.raises(ValueError):
+
+        msg = "Cannot mask with a boolean indexer containing NA values"
+        with pytest.raises(ValueError, match=msg):
             data[mask]
 
         s = pd.Series(data)

From b55dfd2d78358475132dca2214e1a4641f9a305d Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Mon, 20 Jan 2020 15:52:46 +0100
Subject: [PATCH 03/16] fixes for failing tests

---
 pandas/core/arrays/categorical.py                 | 4 ++--
 pandas/core/arrays/datetimelike.py                | 2 ++
 pandas/tests/indexes/categorical/test_category.py | 5 +++--
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/pandas/core/arrays/categorical.py b/pandas/core/arrays/categorical.py
index 3c717458797b5..2a7293f23278f 100644
--- a/pandas/core/arrays/categorical.py
+++ b/pandas/core/arrays/categorical.py
@@ -2001,12 +2001,12 @@ def __getitem__(self, key):
             else:
                 return self.categories[i]
 
-        if is_list_like(key):
+        if is_list_like(key) and not isinstance(key, tuple):
             key = check_array_indexer(self, key)
 
         result = self._codes[key]
         if result.ndim > 1:
-            return result
+            raise IndexError("Cannot user indexer with multiple dimensions")
         return self._constructor(result, dtype=self.dtype, fastpath=True)
 
     def __setitem__(self, key, value):
diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index 7fb3d31f34e8e..e11053330771b 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -521,6 +521,8 @@ def __getitem__(self, key):
             key = check_array_indexer(self, key)
 
         if com.is_bool_indexer(key):
+            # can still have object dtype
+            key = np.asarray(key, dtype=bool)
             if key.all():
                 key = slice(0, None, None)
             else:
diff --git a/pandas/tests/indexes/categorical/test_category.py b/pandas/tests/indexes/categorical/test_category.py
index e027641288bb9..20e114f2b1fc2 100644
--- a/pandas/tests/indexes/categorical/test_category.py
+++ b/pandas/tests/indexes/categorical/test_category.py
@@ -976,8 +976,9 @@ def test_engine_type(self, dtype, engine_type):
         assert np.issubdtype(ci.codes.dtype, dtype)
         assert isinstance(ci._engine, engine_type)
 
-    def test_getitem_2d_deprecated(self):
+    def test_getitem_raise_2d(self):
         # GH#30588 multi-dim indexing is deprecated, but raising is also acceptable
         idx = self.create_index()
-        with pytest.raises(ValueError, match="cannot mask with array containing NA"):
+        msg = "Cannot user indexer with multiple dimensions"
+        with pytest.raises(IndexError, match=msg):
             idx[:, None]

From 58bfe780130ebbfb3c9e0ec06f0ef357632f7333 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Wed, 22 Jan 2020 10:59:59 +0100
Subject: [PATCH 04/16] remove previous check_bool_array_indexer

---
 doc/source/reference/extensions.rst |  2 +-
 pandas/api/indexers/__init__.py     |  4 +-
 pandas/core/common.py               |  4 +-
 pandas/core/indexers.py             | 84 +++++++++++------------------
 pandas/core/indexing.py             |  4 +-
 5 files changed, 39 insertions(+), 59 deletions(-)

diff --git a/doc/source/reference/extensions.rst b/doc/source/reference/extensions.rst
index c072237850d82..78fdfbfd28144 100644
--- a/doc/source/reference/extensions.rst
+++ b/doc/source/reference/extensions.rst
@@ -66,7 +66,7 @@ behaves correctly.
 .. autosummary::
   :toctree: api/
 
-  api.indexers.check_bool_array_indexer
+  api.indexers.check_array_indexer
 
 
 The sentinel ``pandas.api.extensions.no_default`` is used as the default
diff --git a/pandas/api/indexers/__init__.py b/pandas/api/indexers/__init__.py
index e0050326e791a..826297e6b498f 100644
--- a/pandas/api/indexers/__init__.py
+++ b/pandas/api/indexers/__init__.py
@@ -2,7 +2,7 @@
 Public API for Rolling Window Indexers.
 """
 
-from pandas.core.indexers import check_array_indexer, check_bool_array_indexer
+from pandas.core.indexers import check_array_indexer
 from pandas.core.window.indexers import BaseIndexer
 
-__all__ = ["check_array_indexer", "check_bool_array_indexer", "BaseIndexer"]
+__all__ = ["check_array_indexer", "BaseIndexer"]
diff --git a/pandas/core/common.py b/pandas/core/common.py
index f0fcb736586d6..d8b082e7c0f79 100644
--- a/pandas/core/common.py
+++ b/pandas/core/common.py
@@ -121,8 +121,8 @@ def is_bool_indexer(key: Any) -> bool:
 
     See Also
     --------
-    check_bool_array_indexer : Check that `key`
-        is a valid mask for an array, and convert to an ndarray.
+    check_array_indexer : Check that `key` is a valid array to index,
+        and convert to an ndarray.
     """
     na_msg = "cannot mask with array containing NA / NaN values"
     if isinstance(key, (ABCSeries, np.ndarray, ABCIndex)) or (
diff --git a/pandas/core/indexers.py b/pandas/core/indexers.py
index c59f6536683b3..85a00fca0eccd 100644
--- a/pandas/core/indexers.py
+++ b/pandas/core/indexers.py
@@ -249,33 +249,36 @@ def length_of_indexer(indexer, target=None) -> int:
     raise AssertionError("cannot find the length of the indexer")
 
 
-def check_bool_array_indexer(array: AnyArrayLike, mask: AnyArrayLike) -> np.ndarray:
+def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
     """
-    Check if `mask` is a valid boolean indexer for `array`.
+    Check if `indexer` is a valid array indexer for `array`.
 
-    `array` and `mask` are checked to have the same length, and the
-    dtype is validated.
+    `array` and `indexer` are checked to have the same length, and the
+    dtype is validated. If it is an integer or boolean ExtensionArray, it is
+    checked if there are missing values present, and it is converted to
+    the appropriate numpy array.
 
     .. versionadded:: 1.0.0
 
     Parameters
     ----------
     array : array
-        The array that's being masked.
-    mask : array
-        The boolean array that's masking.
+        The array that's being indexed (only used for the length).
+    indexer : array-like or list-like
+        The array-like that's used to index.
 
     Returns
     -------
     numpy.ndarray
-        The validated boolean mask.
+        The validated indexer.
 
     Raises
     ------
     IndexError
         When the lengths don't match.
     ValueError
-        When `mask` cannot be converted to a bool-dtype ndarray.
+        When `indexer` cannot be converted to a numpy ndarray to index
+        (e.g. presence of missing values).
 
     See Also
     --------
@@ -283,17 +286,18 @@ def check_bool_array_indexer(array: AnyArrayLike, mask: AnyArrayLike) -> np.ndar
 
     Examples
     --------
-    A boolean ndarray is returned when the arguments are all valid.
+    When checking a boolean mask, a boolean ndarray is returned when the
+    arguments are all valid.
 
     >>> mask = pd.array([True, False])
     >>> arr = pd.array([1, 2])
-    >>> pd.api.extensions.check_bool_array_indexer(arr, mask)
+    >>> pd.api.indexers.check_array_indexer(arr, mask)
     array([ True, False])
 
     An IndexError is raised when the lengths don't match.
 
     >>> mask = pd.array([True, False, True])
-    >>> pd.api.extensions.check_bool_array_indexer(arr, mask)
+    >>> pd.api.indexers.check_array_indexer(arr, mask)
     Traceback (most recent call last):
     ...
     IndexError: Item wrong length 3 instead of 2.
@@ -302,53 +306,29 @@ def check_bool_array_indexer(array: AnyArrayLike, mask: AnyArrayLike) -> np.ndar
     a bool-dtype ndarray.
 
     >>> mask = pd.array([True, pd.NA])
-    >>> pd.api.extensions.check_bool_array_indexer(arr, mask)
+    >>> pd.api.indexers.check_array_indexer(arr, mask)
     Traceback (most recent call last):
     ...
-    ValueError: cannot convert to bool numpy array in presence of missing values
-    """
-    result = np.asarray(mask, dtype=bool)
-    # GH26658
-    if len(result) != len(array):
-        raise IndexError(f"Item wrong length {len(result)} instead of {len(array)}.")
-    return result
+    ValueError: Cannot mask with a boolean indexer containing NA values
 
+    Similarly for integer indexers, an integer ndarray is returned when it is
+    a valid indexer, otherwise an error is  (for integer indexers, a matching
+    length is not required):
 
-def check_array_indexer(array, indexer) -> np.ndarray:
-    """
-    Check if `indexer` is a valid array indexer for `array`.
-
-    `array` and `indexer` are checked to have the same length, and the
-    dtype is validated. If it is an integer or boolean ExtensionArray, it is
-    checked if there are missing values present, and it is converted to
-    the appropriate numpy array.
-
-    .. versionadded:: 1.0.0
-
-    Parameters
-    ----------
-    array : array
-        The array that's being indexed (only used for the length).
-    indexer : array-like
-        The array-like that's used to index.
-
-    Returns
-    -------
-    numpy.ndarray
-        The validated indexer.
-
-    Raises
-    ------
-    IndexError
-        When the lengths don't match.
-    ValueError
-        When `indexer` cannot be converted to a numpy ndarray.
+    >>> indexer = pd.array([0, 2], dtype="Int64")
+    >>> arr = pd.array([1, 2, 3])
+    >>> pd.api.indexers.check_array_indexer(arr, indexer)
+    array([0, 2])
 
+    >>> indexer = pd.array([0, pd.NA], dtype="Int64")
+    Traceback (most recent call last):
+    ...
+    ValueError: Cannot index with an integer indexer containing NA values
     """
-    import pandas as pd
+    from pandas.core.construction import array as pd_array
 
     if not is_array_like(indexer):
-        indexer = pd.array(indexer)
+        indexer = pd_array(indexer)
     dtype = indexer.dtype
     if is_bool_dtype(dtype):
         try:
@@ -364,7 +344,7 @@ def check_array_indexer(array, indexer) -> np.ndarray:
 
     elif is_integer_dtype(dtype):
         try:
-            indexer = np.asarray(indexer, dtype=int)
+            indexer = np.asarray(indexer, dtype=np.intp)
         except ValueError:
             raise ValueError(
                 "Cannot index with an integer indexer containing NA values"
diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index 63a86792082da..a33724c8d2123 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -23,7 +23,7 @@
 
 import pandas.core.common as com
 from pandas.core.indexers import (
-    check_bool_array_indexer,
+    check_array_indexer,
     is_list_like_indexer,
     length_of_indexer,
 )
@@ -2232,7 +2232,7 @@ def check_bool_indexer(index: Index, key) -> np.ndarray:
     else:
         if is_sparse(result):
             result = result.to_dense()
-        result = check_bool_array_indexer(index, result)
+        result = check_array_indexer(index, result)
 
     return result
 

From 5ce8d857dd909934774042898cbd783137308a79 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Wed, 22 Jan 2020 11:08:03 +0100
Subject: [PATCH 05/16] don't convert tuples to avoid warning from numpy

---
 pandas/core/arrays/datetimelike.py                | 2 +-
 pandas/tests/indexes/categorical/test_category.py | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index e11053330771b..12e06d75548c2 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -517,7 +517,7 @@ def __getitem__(self, key):
                 return self._box_func(val)
             return type(self)(val, dtype=self.dtype)
 
-        if is_list_like(key):
+        if is_list_like(key) and not isinstance(key, tuple):
             key = check_array_indexer(self, key)
 
         if com.is_bool_indexer(key):
diff --git a/pandas/tests/indexes/categorical/test_category.py b/pandas/tests/indexes/categorical/test_category.py
index 20e114f2b1fc2..92169a49af838 100644
--- a/pandas/tests/indexes/categorical/test_category.py
+++ b/pandas/tests/indexes/categorical/test_category.py
@@ -976,7 +976,7 @@ def test_engine_type(self, dtype, engine_type):
         assert np.issubdtype(ci.codes.dtype, dtype)
         assert isinstance(ci._engine, engine_type)
 
-    def test_getitem_raise_2d(self):
+    def test_getitem_2d_deprecated(self):
         # GH#30588 multi-dim indexing is deprecated, but raising is also acceptable
         idx = self.create_index()
         msg = "Cannot user indexer with multiple dimensions"

From ebc21507bda3bc2d0228ec42553a3efa12d65cd4 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Wed, 22 Jan 2020 11:54:41 +0100
Subject: [PATCH 06/16] ensure check_bool_indexer returns numpy array

---
 pandas/core/indexers.py | 4 ++--
 pandas/core/indexing.py | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/core/indexers.py b/pandas/core/indexers.py
index 85a00fca0eccd..997d229932cf3 100644
--- a/pandas/core/indexers.py
+++ b/pandas/core/indexers.py
@@ -262,8 +262,8 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
 
     Parameters
     ----------
-    array : array
-        The array that's being indexed (only used for the length).
+    array : array-like
+        The array that is being indexed (only used for the length).
     indexer : array-like or list-like
         The array-like that's used to index.
 
diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index a33724c8d2123..9d18080493d56 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -2232,7 +2232,7 @@ def check_bool_indexer(index: Index, key) -> np.ndarray:
     else:
         if is_sparse(result):
             result = result.to_dense()
-        result = check_array_indexer(index, result)
+        result = np.asarray(check_array_indexer(index, result), dtype=bool)
 
     return result
 

From 4a51d9700bbc850d8a6d484d1326e83146520435 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Wed, 22 Jan 2020 12:46:29 +0100
Subject: [PATCH 07/16] raise warning for categorical

---
 pandas/core/arrays/categorical.py                 | 5 ++++-
 pandas/tests/indexes/categorical/test_category.py | 7 -------
 2 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/pandas/core/arrays/categorical.py b/pandas/core/arrays/categorical.py
index 2a7293f23278f..4f50c9efc83b6 100644
--- a/pandas/core/arrays/categorical.py
+++ b/pandas/core/arrays/categorical.py
@@ -2006,7 +2006,10 @@ def __getitem__(self, key):
 
         result = self._codes[key]
         if result.ndim > 1:
-            raise IndexError("Cannot user indexer with multiple dimensions")
+            from pandas.core.indexes.base import deprecate_ndim_indexing
+
+            deprecate_ndim_indexing(result)
+            return result
         return self._constructor(result, dtype=self.dtype, fastpath=True)
 
     def __setitem__(self, key, value):
diff --git a/pandas/tests/indexes/categorical/test_category.py b/pandas/tests/indexes/categorical/test_category.py
index 92169a49af838..d09dc586fe056 100644
--- a/pandas/tests/indexes/categorical/test_category.py
+++ b/pandas/tests/indexes/categorical/test_category.py
@@ -975,10 +975,3 @@ def test_engine_type(self, dtype, engine_type):
             ci.values._codes = ci.values._codes.astype("int64")
         assert np.issubdtype(ci.codes.dtype, dtype)
         assert isinstance(ci._engine, engine_type)
-
-    def test_getitem_2d_deprecated(self):
-        # GH#30588 multi-dim indexing is deprecated, but raising is also acceptable
-        idx = self.create_index()
-        msg = "Cannot user indexer with multiple dimensions"
-        with pytest.raises(IndexError, match=msg):
-            idx[:, None]

From c979df806de96e2d7fab1a29df4211157e82d67a Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Fri, 24 Jan 2020 17:17:07 +0100
Subject: [PATCH 08/16] move deprecate_ndim_indexing

---
 pandas/core/arrays/categorical.py |  4 +---
 pandas/core/indexers.py           | 21 +++++++++++++++++++++
 pandas/core/indexes/base.py       | 16 +---------------
 pandas/core/indexes/extension.py  |  3 ++-
 4 files changed, 25 insertions(+), 19 deletions(-)

diff --git a/pandas/core/arrays/categorical.py b/pandas/core/arrays/categorical.py
index 4f50c9efc83b6..03e9b5cacf4b3 100644
--- a/pandas/core/arrays/categorical.py
+++ b/pandas/core/arrays/categorical.py
@@ -54,7 +54,7 @@
 from pandas.core.base import NoNewAttributesMixin, PandasObject, _shared_docs
 import pandas.core.common as com
 from pandas.core.construction import array, extract_array, sanitize_array
-from pandas.core.indexers import check_array_indexer
+from pandas.core.indexers import check_array_indexer, deprecate_ndim_indexing
 from pandas.core.missing import interpolate_2d
 from pandas.core.ops.common import unpack_zerodim_and_defer
 from pandas.core.sorting import nargsort
@@ -2006,8 +2006,6 @@ def __getitem__(self, key):
 
         result = self._codes[key]
         if result.ndim > 1:
-            from pandas.core.indexes.base import deprecate_ndim_indexing
-
             deprecate_ndim_indexing(result)
             return result
         return self._constructor(result, dtype=self.dtype, fastpath=True)
diff --git a/pandas/core/indexers.py b/pandas/core/indexers.py
index 997d229932cf3..450c046da404f 100644
--- a/pandas/core/indexers.py
+++ b/pandas/core/indexers.py
@@ -1,6 +1,8 @@
 """
 Low-dependency indexing utilities.
 """
+import warnings
+
 import numpy as np
 
 from pandas._typing import AnyArrayLike
@@ -249,6 +251,25 @@ def length_of_indexer(indexer, target=None) -> int:
     raise AssertionError("cannot find the length of the indexer")
 
 
+def deprecate_ndim_indexing(result):
+    """
+    Helper function to raise the deprecation warning for multi-dimensional
+    indexing on 1D Series/Index.
+
+    GH#27125 indexer like idx[:, None] expands dim, but we cannot do that
+    and keep an index, so we currently return ndarray, which is deprecated
+    (Deprecation GH#30588).
+    """
+    if np.ndim(result) > 1:
+        warnings.warn(
+            "Support for multi-dimensional indexing (e.g. `index[:, None]`) "
+            "on an Index is deprecated and will be removed in a future "
+            "version.  Convert to a numpy array before indexing instead.",
+            DeprecationWarning,
+            stacklevel=3,
+        )
+
+
 def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
     """
     Check if `indexer` is a valid array indexer for `array`.
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index bab3d2d1b5431..95fa03c60d48e 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -67,7 +67,7 @@
 from pandas.core.arrays import ExtensionArray
 from pandas.core.base import IndexOpsMixin, PandasObject
 import pandas.core.common as com
-from pandas.core.indexers import maybe_convert_indices
+from pandas.core.indexers import deprecate_ndim_indexing, maybe_convert_indices
 from pandas.core.indexes.frozen import FrozenList
 import pandas.core.missing as missing
 from pandas.core.ops import get_op_result_name
@@ -5819,17 +5819,3 @@ def _try_convert_to_int_array(
         pass
 
     raise ValueError
-
-
-def deprecate_ndim_indexing(result):
-    if np.ndim(result) > 1:
-        # GH#27125 indexer like idx[:, None] expands dim, but we
-        #  cannot do that and keep an index, so return ndarray
-        # Deprecation GH#30588
-        warnings.warn(
-            "Support for multi-dimensional indexing (e.g. `index[:, None]`) "
-            "on an Index is deprecated and will be removed in a future "
-            "version.  Convert to a numpy array before indexing instead.",
-            DeprecationWarning,
-            stacklevel=3,
-        )
diff --git a/pandas/core/indexes/extension.py b/pandas/core/indexes/extension.py
index 9ddc5c01030b1..c99f2a1e47b54 100644
--- a/pandas/core/indexes/extension.py
+++ b/pandas/core/indexes/extension.py
@@ -12,7 +12,8 @@
 from pandas.core.dtypes.generic import ABCSeries
 
 from pandas.core.arrays import ExtensionArray
-from pandas.core.indexes.base import Index, deprecate_ndim_indexing
+from pandas.core.indexers import deprecate_ndim_indexing
+from pandas.core.indexes.base import Index
 from pandas.core.ops import get_op_result_name
 
 

From ce2e04297182be3041aa272695dbc7236924bda7 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Fri, 24 Jan 2020 17:38:24 +0100
Subject: [PATCH 09/16] cleanup; ensure output of check_array_indexer is always
 an ndarray

---
 pandas/core/indexers.py            | 41 +++++++++++++++++++++++-------
 pandas/tests/indexing/test_iloc.py |  6 ++++-
 pandas/tests/indexing/test_loc.py  |  6 ++++-
 3 files changed, 42 insertions(+), 11 deletions(-)

diff --git a/pandas/core/indexers.py b/pandas/core/indexers.py
index 450c046da404f..164d4be849d35 100644
--- a/pandas/core/indexers.py
+++ b/pandas/core/indexers.py
@@ -270,14 +270,18 @@ def deprecate_ndim_indexing(result):
         )
 
 
+# -----------------------------------------------------------
+# Public indexer validation
+
+
 def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
     """
     Check if `indexer` is a valid array indexer for `array`.
 
-    `array` and `indexer` are checked to have the same length, and the
-    dtype is validated. If it is an integer or boolean ExtensionArray, it is
-    checked if there are missing values present, and it is converted to
-    the appropriate numpy array.
+    For a boolean mask, `array` and `indexer` are checked to have the same
+    length. The dtype is validated, and if it is an integer or boolean
+    ExtensionArray, it is checked if there are missing values present, and
+    it is converted to the appropriate numpy array.
 
     .. versionadded:: 1.0.0
 
@@ -286,12 +290,14 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
     array : array-like
         The array that is being indexed (only used for the length).
     indexer : array-like or list-like
-        The array-like that's used to index.
+        The array-like that's used to index. The function assumes this is an
+        array-like, and input that is not yet an numpy array or an ExtensionArray
+        is converted to one.
 
     Returns
     -------
     numpy.ndarray
-        The validated indexer.
+        The validated indexer as a numpy array that can be used to index.
 
     Raises
     ------
@@ -321,7 +327,7 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
     >>> pd.api.indexers.check_array_indexer(arr, mask)
     Traceback (most recent call last):
     ...
-    IndexError: Item wrong length 3 instead of 2.
+    IndexError: Boolean index has wrong length: 3 instead of 2.
 
     A ValueError is raised when the mask cannot be converted to
     a bool-dtype ndarray.
@@ -332,6 +338,12 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
     ...
     ValueError: Cannot mask with a boolean indexer containing NA values
 
+    A numpy boolean mask will get passed through (if the length is correct):
+
+    >>> mask = np.array([True, False])
+    >>> pd.api.indexers.check_array_indexer(arr, mask)
+    array([ True, False])
+
     Similarly for integer indexers, an integer ndarray is returned when it is
     a valid indexer, otherwise an error is  (for integer indexers, a matching
     length is not required):
@@ -342,9 +354,18 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
     array([0, 2])
 
     >>> indexer = pd.array([0, pd.NA], dtype="Int64")
+    >>> pd.api.indexers.check_array_indexer(arr, indexer)
     Traceback (most recent call last):
     ...
     ValueError: Cannot index with an integer indexer containing NA values
+
+    For non-integer/boolean dtypes, an appropriate error is raised:
+
+    >>> indexer = np.array([0., 2.], dtype="float64")
+    >>> pd.api.indexers.check_array_indexer(arr, indexer)
+    Traceback (most recent call last):
+    ...
+    IndexError: arrays used as indices must be of integer or boolean type
     """
     from pandas.core.construction import array as pd_array
 
@@ -360,9 +381,9 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
         # GH26658
         if len(indexer) != len(array):
             raise IndexError(
-                f"Item wrong length {len(indexer)} instead of {len(array)}."
+                f"Boolean index has wrong length: "
+                f"{len(indexer)} instead of {len(array)}"
             )
-
     elif is_integer_dtype(dtype):
         try:
             indexer = np.asarray(indexer, dtype=np.intp)
@@ -370,5 +391,7 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
             raise ValueError(
                 "Cannot index with an integer indexer containing NA values"
             )
+    else:
+        raise IndexError("arrays used as indices must be of integer or boolean type")
 
     return indexer
diff --git a/pandas/tests/indexing/test_iloc.py b/pandas/tests/indexing/test_iloc.py
index 48c25ec034653..11c9d5213fe95 100644
--- a/pandas/tests/indexing/test_iloc.py
+++ b/pandas/tests/indexing/test_iloc.py
@@ -251,7 +251,11 @@ def test_iloc_getitem_bool_diff_len(self, index):
         s = Series([1, 2, 3])
         with pytest.raises(
             IndexError,
-            match=("Item wrong length {} instead of {}.".format(len(index), len(s))),
+            match=(
+                "Boolean index has wrong length: {} instead of {}".format(
+                    len(index), len(s)
+                )
+            ),
         ):
             _ = s.iloc[index]
 
diff --git a/pandas/tests/indexing/test_loc.py b/pandas/tests/indexing/test_loc.py
index 4c1436b800fc3..d5a890a8694a6 100644
--- a/pandas/tests/indexing/test_loc.py
+++ b/pandas/tests/indexing/test_loc.py
@@ -202,7 +202,11 @@ def test_loc_getitem_bool_diff_len(self, index):
         s = Series([1, 2, 3])
         with pytest.raises(
             IndexError,
-            match=("Item wrong length {} instead of {}.".format(len(index), len(s))),
+            match=(
+                "Boolean index has wrong length: {} instead of {}".format(
+                    len(index), len(s)
+                )
+            ),
         ):
             _ = s.loc[index]
 

From 4d447bf030b8eb5886fd7622cc930d9a076f3f7d Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Fri, 24 Jan 2020 17:41:05 +0100
Subject: [PATCH 10/16] clean-up black reformatting

---
 pandas/tests/indexing/test_iloc.py | 12 ++++--------
 pandas/tests/indexing/test_loc.py  | 12 ++++--------
 2 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/pandas/tests/indexing/test_iloc.py b/pandas/tests/indexing/test_iloc.py
index 11c9d5213fe95..d67259e8b7d40 100644
--- a/pandas/tests/indexing/test_iloc.py
+++ b/pandas/tests/indexing/test_iloc.py
@@ -249,14 +249,10 @@ def test_iloc_getitem_bool(self):
     def test_iloc_getitem_bool_diff_len(self, index):
         # GH26658
         s = Series([1, 2, 3])
-        with pytest.raises(
-            IndexError,
-            match=(
-                "Boolean index has wrong length: {} instead of {}".format(
-                    len(index), len(s)
-                )
-            ),
-        ):
+        msg = "Boolean index has wrong length: {} instead of {}".format(
+            len(index), len(s)
+        )
+        with pytest.raises(IndexError, match=msg):
             _ = s.iloc[index]
 
     def test_iloc_getitem_slice(self):
diff --git a/pandas/tests/indexing/test_loc.py b/pandas/tests/indexing/test_loc.py
index d5a890a8694a6..b9dc96adfa738 100644
--- a/pandas/tests/indexing/test_loc.py
+++ b/pandas/tests/indexing/test_loc.py
@@ -200,14 +200,10 @@ def test_loc_getitem_bool(self):
     def test_loc_getitem_bool_diff_len(self, index):
         # GH26658
         s = Series([1, 2, 3])
-        with pytest.raises(
-            IndexError,
-            match=(
-                "Boolean index has wrong length: {} instead of {}".format(
-                    len(index), len(s)
-                )
-            ),
-        ):
+        msg = "Boolean index has wrong length: {} instead of {}".format(
+            len(index), len(s)
+        )
+        with pytest.raises(IndexError, match=msg):
             _ = s.loc[index]
 
     def test_loc_getitem_int_slice(self):

From 9ed8fe9c34c0898be95faf3e79a69caacf84c2e4 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Tue, 28 Jan 2020 07:39:45 +0100
Subject: [PATCH 11/16] fix check_bool_indexer

---
 pandas/core/indexing.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index 11c5725b5ddce..fcdaeb68dbde2 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -2232,7 +2232,7 @@ def check_bool_indexer(index: Index, key) -> np.ndarray:
     else:
         if is_sparse(result):
             result = np.asarray(result)
-        result = np.asarray(check_array_indexer(index, result), dtype=bool)
+        result = check_array_indexer(index, np.asarray(result, dtype=bool))
 
     return result
 

From 2f8cd276e6e7bc2be3c8dfa4a8d94855187c5654 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Tue, 28 Jan 2020 08:03:52 +0100
Subject: [PATCH 12/16] add comment to check_bool_indexer

---
 pandas/core/indexing.py | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index fcdaeb68dbde2..fb49da0352b60 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -15,7 +15,6 @@
     is_numeric_dtype,
     is_scalar,
     is_sequence,
-    is_sparse,
 )
 from pandas.core.dtypes.concat import concat_compat
 from pandas.core.dtypes.generic import ABCDataFrame, ABCMultiIndex, ABCSeries
@@ -2230,9 +2229,9 @@ def check_bool_indexer(index: Index, key) -> np.ndarray:
             )
         result = result.astype(bool)._values
     else:
-        if is_sparse(result):
-            result = np.asarray(result)
-        result = check_array_indexer(index, np.asarray(result, dtype=bool))
+        # key might be sparse / object-dtype bool, check_array_indexer needs bool array
+        result = np.asarray(result, dtype=bool)
+        result = check_array_indexer(index, result)
 
     return result
 

From 4d9a201664adbf46833f3765f0f18e286c033d91 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Tue, 28 Jan 2020 10:12:14 +0100
Subject: [PATCH 13/16] fix empty list case

---
 pandas/core/arrays/datetimelike.py     |  9 +++++----
 pandas/core/indexers.py                |  3 +++
 pandas/tests/extension/base/getitem.py | 14 +++++++++++++-
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index 12e06d75548c2..2c1aad436b6c9 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -517,16 +517,17 @@ def __getitem__(self, key):
                 return self._box_func(val)
             return type(self)(val, dtype=self.dtype)
 
-        if is_list_like(key) and not isinstance(key, tuple):
-            key = check_array_indexer(self, key)
-
         if com.is_bool_indexer(key):
-            # can still have object dtype
+            # first check for boolean, because check_array_indexer doesn't
+            # allow object dtype
             key = np.asarray(key, dtype=bool)
+            key = check_array_indexer(self, key)
             if key.all():
                 key = slice(0, None, None)
             else:
                 key = lib.maybe_booleans_to_slice(key.view(np.uint8))
+        elif is_list_like(key) and not isinstance(key, tuple):
+            key = check_array_indexer(self, key)
 
         is_period = is_period_dtype(self)
         if is_period:
diff --git a/pandas/core/indexers.py b/pandas/core/indexers.py
index 164d4be849d35..5adb58d6defcb 100644
--- a/pandas/core/indexers.py
+++ b/pandas/core/indexers.py
@@ -371,6 +371,9 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
 
     if not is_array_like(indexer):
         indexer = pd_array(indexer)
+        if len(indexer) == 0:
+            # empty list is converted to float array by pd.array
+            indexer = np.array([], dtype=np.intp)
     dtype = indexer.dtype
     if is_bool_dtype(dtype):
         try:
diff --git a/pandas/tests/extension/base/getitem.py b/pandas/tests/extension/base/getitem.py
index 8a05ab4ddaa1b..8615a8df22dcc 100644
--- a/pandas/tests/extension/base/getitem.py
+++ b/pandas/tests/extension/base/getitem.py
@@ -97,6 +97,15 @@ def test_getitem_scalar_na(self, data_missing, na_cmp, na_value):
         result = data_missing[0]
         assert na_cmp(result, na_value)
 
+    def test_getitem_empty(self, data):
+        # Indexing with empty list
+        result = data[[]]
+        assert len(result) == 0
+        assert isinstance(result, type(data))
+
+        expected = data[np.array([], dtype="int64")]
+        self.assert_extension_array_equal(result, expected)
+
     def test_getitem_mask(self, data):
         # Empty mask, raw array
         mask = np.zeros(len(data), dtype=bool)
@@ -153,7 +162,10 @@ def test_getitem_boolean_array_mask_raises(self, data):
         mask = pd.array(np.zeros(data.shape, dtype="bool"), dtype="boolean")
         mask[:2] = pd.NA
 
-        msg = "Cannot mask with a boolean indexer containing NA values"
+        msg = (
+            "Cannot mask with a boolean indexer containing NA values|"
+            "cannot mask with array containing NA / NaN values"
+        )
         with pytest.raises(ValueError, match=msg):
             data[mask]
 

From 097d221f3e49d3346ea78687f46cea1698d14e3c Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Tue, 28 Jan 2020 10:35:13 +0100
Subject: [PATCH 14/16] add specific tests for check_array_indexer

---
 pandas/tests/indexing/test_check_indexer.py | 87 +++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 pandas/tests/indexing/test_check_indexer.py

diff --git a/pandas/tests/indexing/test_check_indexer.py b/pandas/tests/indexing/test_check_indexer.py
new file mode 100644
index 0000000000000..33c6bc3372083
--- /dev/null
+++ b/pandas/tests/indexing/test_check_indexer.py
@@ -0,0 +1,87 @@
+import numpy as np
+import pytest
+
+import pandas as pd
+import pandas._testing as tm
+from pandas.api.indexers import check_array_indexer
+
+
+@pytest.mark.parametrize(
+    "indexer, expected",
+    [
+        # integer
+        ([1, 2], np.array([1, 2], dtype=np.intp)),
+        (np.array([1, 2], dtype="int64"), np.array([1, 2], dtype=np.intp)),
+        (pd.array([1, 2], dtype="Int32"), np.array([1, 2], dtype=np.intp)),
+        (pd.Index([1, 2]), np.array([1, 2], dtype=np.intp)),
+        # boolean
+        ([True, False, True], np.array([True, False, True], dtype=np.bool_)),
+        (np.array([True, False, True]), np.array([True, False, True], dtype=np.bool_)),
+        (
+            pd.array([True, False, True], dtype="boolean"),
+            np.array([True, False, True], dtype=np.bool_),
+        ),
+        # other
+        ([], np.array([], dtype=np.intp)),
+    ],
+)
+def test_valid_input(indexer, expected):
+    array = np.array([1, 2, 3])
+    result = check_array_indexer(array, indexer)
+    tm.assert_numpy_array_equal(result, expected)
+
+
+@pytest.mark.parametrize(
+    "indexer", [[True, False, None], pd.array([True, False, None], dtype="boolean")],
+)
+def test_bool_raise_missing_values(indexer):
+    array = np.array([1, 2, 3])
+
+    msg = "Cannot mask with a boolean indexer containing NA values"
+    with pytest.raises(ValueError, match=msg):
+        check_array_indexer(array, indexer)
+
+
+@pytest.mark.parametrize(
+    "indexer",
+    [
+        [True, False],
+        pd.array([True, False], dtype="boolean"),
+        np.array([True, False], dtype=np.bool_),
+    ],
+)
+def test_bool_raise_length(indexer):
+    array = np.array([1, 2, 3])
+
+    msg = "Boolean index has wrong length"
+    with pytest.raises(IndexError, match=msg):
+        check_array_indexer(array, indexer)
+
+
+@pytest.mark.parametrize(
+    "indexer", [[0, 1, None], pd.array([0, 1, pd.NA], dtype="Int64")],
+)
+def test_int_raise_missing_values(indexer):
+    array = np.array([1, 2, 3])
+
+    msg = "Cannot index with an integer indexer containing NA values"
+    with pytest.raises(ValueError, match=msg):
+        check_array_indexer(array, indexer)
+
+
+@pytest.mark.parametrize(
+    "indexer",
+    [
+        [0.0, 1.0],
+        np.array([1.0, 2.0], dtype="float64"),
+        np.array([True, False], dtype=object),
+        pd.Index([True, False], dtype=object),
+        pd.array(["a", "b"], dtype="string"),
+    ],
+)
+def test_raise_invalid_array_dtypes(indexer):
+    array = np.array([1, 2, 3])
+
+    msg = "arrays used as indices must be of integer or boolean type"
+    with pytest.raises(IndexError, match=msg):
+        check_array_indexer(array, indexer)

From 3c5e4c68873e641f0f2dffed35d74e0a64908aa1 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Tue, 28 Jan 2020 12:03:09 +0100
Subject: [PATCH 15/16] allow list-length-1-with-slice corner case

---
 pandas/core/arrays/datetimelike.py | 6 +++++-
 pandas/core/arrays/interval.py     | 2 +-
 pandas/core/arrays/masked.py       | 2 +-
 pandas/core/arrays/numpy_.py       | 2 +-
 pandas/core/arrays/sparse/array.py | 2 +-
 5 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index 2c1aad436b6c9..319caa53dc3c1 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -518,7 +518,7 @@ def __getitem__(self, key):
             return type(self)(val, dtype=self.dtype)
 
         if com.is_bool_indexer(key):
-            # first check for boolean, because check_array_indexer doesn't
+            # first convert to boolean, because check_array_indexer doesn't
             # allow object dtype
             key = np.asarray(key, dtype=bool)
             key = check_array_indexer(self, key)
@@ -526,6 +526,10 @@ def __getitem__(self, key):
                 key = slice(0, None, None)
             else:
                 key = lib.maybe_booleans_to_slice(key.view(np.uint8))
+        elif isinstance(key, list) and len(key) == 1 and isinstance(key[0], slice):
+            # see https://github.com/pandas-dev/pandas/issues/31299, need to allow
+            # this for now (would otherwise raise in check_array_indexer)
+            pass
         elif is_list_like(key) and not isinstance(key, tuple):
             key = check_array_indexer(self, key)
 
diff --git a/pandas/core/arrays/interval.py b/pandas/core/arrays/interval.py
index 23f2151bb593a..055c772d66485 100644
--- a/pandas/core/arrays/interval.py
+++ b/pandas/core/arrays/interval.py
@@ -496,7 +496,7 @@ def __len__(self) -> int:
         return len(self.left)
 
     def __getitem__(self, value):
-        if is_list_like(value):
+        if is_list_like(value) and not isinstance(value, tuple):
             value = check_array_indexer(self, value)
         left = self.left[value]
         right = self.right[value]
diff --git a/pandas/core/arrays/masked.py b/pandas/core/arrays/masked.py
index 6bd21df434528..2c3e51960622d 100644
--- a/pandas/core/arrays/masked.py
+++ b/pandas/core/arrays/masked.py
@@ -39,7 +39,7 @@ def __getitem__(self, item):
                 return self.dtype.na_value
             return self._data[item]
 
-        elif is_list_like(item):
+        elif is_list_like(item) and not isinstance(item, tuple):
             item = check_array_indexer(self, item)
 
         return type(self)(self._data[item], self._mask[item])
diff --git a/pandas/core/arrays/numpy_.py b/pandas/core/arrays/numpy_.py
index 56b362e3db7a3..73bc22d199f37 100644
--- a/pandas/core/arrays/numpy_.py
+++ b/pandas/core/arrays/numpy_.py
@@ -234,7 +234,7 @@ def __getitem__(self, item):
         if isinstance(item, type(self)):
             item = item._ndarray
 
-        elif is_list_like(item):
+        elif is_list_like(item) and not isinstance(item, tuple):
             item = check_array_indexer(self, item)
 
         result = self._ndarray[item]
diff --git a/pandas/core/arrays/sparse/array.py b/pandas/core/arrays/sparse/array.py
index c499218c2e947..078e6c2f119d2 100644
--- a/pandas/core/arrays/sparse/array.py
+++ b/pandas/core/arrays/sparse/array.py
@@ -770,7 +770,7 @@ def __getitem__(self, key):
                 else:
                     key = np.asarray(key)
 
-            if is_list_like(key):
+            if is_list_like(key) and not isinstance(key, tuple):
                 key = check_array_indexer(self, key)
 
             if com.is_bool_indexer(key):

From 1ca35d15baffa2e8869b238f57f29e2b01c91332 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Tue, 28 Jan 2020 16:12:57 +0100
Subject: [PATCH 16/16] move list-like check inside

---
 pandas/core/arrays/categorical.py           |  3 +--
 pandas/core/arrays/datetimelike.py          |  2 +-
 pandas/core/arrays/interval.py              |  3 +--
 pandas/core/arrays/masked.py                | 10 ++------
 pandas/core/arrays/numpy_.py                |  4 +--
 pandas/core/arrays/sparse/array.py          |  4 +--
 pandas/core/indexers.py                     | 28 ++++++++++++++++-----
 pandas/tests/extension/decimal/array.py     |  3 +--
 pandas/tests/indexing/test_check_indexer.py | 10 ++++++++
 9 files changed, 40 insertions(+), 27 deletions(-)

diff --git a/pandas/core/arrays/categorical.py b/pandas/core/arrays/categorical.py
index 03e9b5cacf4b3..412422397af06 100644
--- a/pandas/core/arrays/categorical.py
+++ b/pandas/core/arrays/categorical.py
@@ -2001,8 +2001,7 @@ def __getitem__(self, key):
             else:
                 return self.categories[i]
 
-        if is_list_like(key) and not isinstance(key, tuple):
-            key = check_array_indexer(self, key)
+        key = check_array_indexer(self, key)
 
         result = self._codes[key]
         if result.ndim > 1:
diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index 319caa53dc3c1..0ea707e1ae69d 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -530,7 +530,7 @@ def __getitem__(self, key):
             # see https://github.com/pandas-dev/pandas/issues/31299, need to allow
             # this for now (would otherwise raise in check_array_indexer)
             pass
-        elif is_list_like(key) and not isinstance(key, tuple):
+        else:
             key = check_array_indexer(self, key)
 
         is_period = is_period_dtype(self)
diff --git a/pandas/core/arrays/interval.py b/pandas/core/arrays/interval.py
index 055c772d66485..d890c0c16aecc 100644
--- a/pandas/core/arrays/interval.py
+++ b/pandas/core/arrays/interval.py
@@ -496,8 +496,7 @@ def __len__(self) -> int:
         return len(self.left)
 
     def __getitem__(self, value):
-        if is_list_like(value) and not isinstance(value, tuple):
-            value = check_array_indexer(self, value)
+        value = check_array_indexer(self, value)
         left = self.left[value]
         right = self.right[value]
 
diff --git a/pandas/core/arrays/masked.py b/pandas/core/arrays/masked.py
index 2c3e51960622d..80e317123126a 100644
--- a/pandas/core/arrays/masked.py
+++ b/pandas/core/arrays/masked.py
@@ -4,12 +4,7 @@
 
 from pandas._libs import lib, missing as libmissing
 
-from pandas.core.dtypes.common import (
-    is_integer,
-    is_list_like,
-    is_object_dtype,
-    is_string_dtype,
-)
+from pandas.core.dtypes.common import is_integer, is_object_dtype, is_string_dtype
 from pandas.core.dtypes.missing import isna, notna
 
 from pandas.core.algorithms import take
@@ -39,8 +34,7 @@ def __getitem__(self, item):
                 return self.dtype.na_value
             return self._data[item]
 
-        elif is_list_like(item) and not isinstance(item, tuple):
-            item = check_array_indexer(self, item)
+        item = check_array_indexer(self, item)
 
         return type(self)(self._data[item], self._mask[item])
 
diff --git a/pandas/core/arrays/numpy_.py b/pandas/core/arrays/numpy_.py
index 73bc22d199f37..8b1d1e58dc36c 100644
--- a/pandas/core/arrays/numpy_.py
+++ b/pandas/core/arrays/numpy_.py
@@ -9,7 +9,6 @@
 from pandas.util._decorators import Appender
 from pandas.util._validators import validate_fillna_kwargs
 
-from pandas.core.dtypes.common import is_list_like
 from pandas.core.dtypes.dtypes import ExtensionDtype
 from pandas.core.dtypes.generic import ABCIndexClass, ABCSeries
 from pandas.core.dtypes.inference import is_array_like
@@ -234,8 +233,7 @@ def __getitem__(self, item):
         if isinstance(item, type(self)):
             item = item._ndarray
 
-        elif is_list_like(item) and not isinstance(item, tuple):
-            item = check_array_indexer(self, item)
+        item = check_array_indexer(self, item)
 
         result = self._ndarray[item]
         if not lib.is_scalar(item):
diff --git a/pandas/core/arrays/sparse/array.py b/pandas/core/arrays/sparse/array.py
index 078e6c2f119d2..b476a019c66cc 100644
--- a/pandas/core/arrays/sparse/array.py
+++ b/pandas/core/arrays/sparse/array.py
@@ -29,7 +29,6 @@
     is_datetime64_any_dtype,
     is_dtype_equal,
     is_integer,
-    is_list_like,
     is_object_dtype,
     is_scalar,
     is_string_dtype,
@@ -770,8 +769,7 @@ def __getitem__(self, key):
                 else:
                     key = np.asarray(key)
 
-            if is_list_like(key) and not isinstance(key, tuple):
-                key = check_array_indexer(self, key)
+            key = check_array_indexer(self, key)
 
             if com.is_bool_indexer(key):
                 key = check_bool_indexer(self, key)
diff --git a/pandas/core/indexers.py b/pandas/core/indexers.py
index 5adb58d6defcb..fe475527f4596 100644
--- a/pandas/core/indexers.py
+++ b/pandas/core/indexers.py
@@ -5,7 +5,7 @@
 
 import numpy as np
 
-from pandas._typing import AnyArrayLike
+from pandas._typing import Any, AnyArrayLike
 
 from pandas.core.dtypes.common import (
     is_array_like,
@@ -274,14 +274,18 @@ def deprecate_ndim_indexing(result):
 # Public indexer validation
 
 
-def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
+def check_array_indexer(array: AnyArrayLike, indexer: Any) -> Any:
     """
     Check if `indexer` is a valid array indexer for `array`.
 
     For a boolean mask, `array` and `indexer` are checked to have the same
     length. The dtype is validated, and if it is an integer or boolean
     ExtensionArray, it is checked if there are missing values present, and
-    it is converted to the appropriate numpy array.
+    it is converted to the appropriate numpy array. Other dtypes will raise
+    an error.
+
+    Non-array indexers (integer, slice, Ellipsis, tuples, ..) are passed
+    through as is.
 
     .. versionadded:: 1.0.0
 
@@ -290,9 +294,9 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
     array : array-like
         The array that is being indexed (only used for the length).
     indexer : array-like or list-like
-        The array-like that's used to index. The function assumes this is an
-        array-like, and input that is not yet an numpy array or an ExtensionArray
-        is converted to one.
+        The array-like that's used to index. List-like input that is not yet
+        a numpy array or an ExtensionArray is converted to one. Other input
+        types are passed through as is
 
     Returns
     -------
@@ -369,11 +373,23 @@ def check_array_indexer(array: AnyArrayLike, indexer) -> np.ndarray:
     """
     from pandas.core.construction import array as pd_array
 
+    # whathever is not an array-like is returned as-is (possible valid array
+    # indexers that are not array-like: integer, slice, Ellipsis, None)
+    # In this context, tuples are not considered as array-like, as they have
+    # a specific meaning in indexing (multi-dimensional indexing)
+    if is_list_like(indexer):
+        if isinstance(indexer, tuple):
+            return indexer
+    else:
+        return indexer
+
+    # convert list-likes to array
     if not is_array_like(indexer):
         indexer = pd_array(indexer)
         if len(indexer) == 0:
             # empty list is converted to float array by pd.array
             indexer = np.array([], dtype=np.intp)
+
     dtype = indexer.dtype
     if is_bool_dtype(dtype):
         try:
diff --git a/pandas/tests/extension/decimal/array.py b/pandas/tests/extension/decimal/array.py
index 12a906b5afbe1..743852c35dbd8 100644
--- a/pandas/tests/extension/decimal/array.py
+++ b/pandas/tests/extension/decimal/array.py
@@ -116,8 +116,7 @@ def __getitem__(self, item):
             return self._data[item]
         else:
             # array, slice.
-            if pd.api.types.is_list_like(item):
-                item = pd.api.indexers.check_array_indexer(self, item)
+            item = pd.api.indexers.check_array_indexer(self, item)
             return type(self)(self._data[item])
 
     def take(self, indexer, allow_fill=False, fill_value=None):
diff --git a/pandas/tests/indexing/test_check_indexer.py b/pandas/tests/indexing/test_check_indexer.py
index 33c6bc3372083..82f8c12229824 100644
--- a/pandas/tests/indexing/test_check_indexer.py
+++ b/pandas/tests/indexing/test_check_indexer.py
@@ -85,3 +85,13 @@ def test_raise_invalid_array_dtypes(indexer):
     msg = "arrays used as indices must be of integer or boolean type"
     with pytest.raises(IndexError, match=msg):
         check_array_indexer(array, indexer)
+
+
+@pytest.mark.parametrize(
+    "indexer", [None, Ellipsis, slice(0, 3), (None,)],
+)
+def test_pass_through_non_array_likes(indexer):
+    array = np.array([1, 2, 3])
+
+    result = check_array_indexer(array, indexer)
+    assert result == indexer