COMPAT: fixup decimal extension for indexing compat (#19882)

Author: jreback

pandas/tests/extension/base/getitem.py

@@ -18,7 +18,8 @@ def test_iloc_series(self, data):
         self.assert_series_equal(result, expected)
 
     def test_iloc_frame(self, data):
-        df = pd.DataFrame({"A": data, 'B': np.arange(len(data))})
+        df = pd.DataFrame({"A": data, 'B':
+                           np.arange(len(data), dtype='int64')})
         expected = pd.DataFrame({"A": data[:4]})
 
         # slice -> frame
@@ -49,7 +50,8 @@ def test_loc_series(self, data):
         self.assert_series_equal(result, expected)
 
     def test_loc_frame(self, data):
-        df = pd.DataFrame({"A": data, 'B': np.arange(len(data))})
+        df = pd.DataFrame({"A": data,
+                           'B': np.arange(len(data), dtype='int64')})
         expected = pd.DataFrame({"A": data[:4]})
 
         # slice -> frame

pandas/tests/extension/decimal/array.py

@@ -8,6 +8,7 @@
 import pandas as pd
 from pandas.core.arrays import ExtensionArray
 from pandas.core.dtypes.base import ExtensionDtype
+from pandas.core.dtypes.common import _ensure_platform_int
 
 
 class DecimalDtype(ExtensionDtype):
@@ -68,6 +69,7 @@ def isna(self):
     def take(self, indexer, allow_fill=True, fill_value=None):
         mask = indexer == -1
 
+        indexer = _ensure_platform_int(indexer)
         out = self.values.take(indexer)
         out[mask] = self._na_value