CoW: Avoid warning for ArrowDtypes when setting inplace

Author: phofl

pandas/core/internals/managers.py

@@ -54,7 +54,11 @@
 )
 
 import pandas.core.algorithms as algos
-from pandas.core.arrays import DatetimeArray
+from pandas.core.arrays import (
+    ArrowExtensionArray,
+    ArrowStringArray,
+    DatetimeArray,
+)
 from pandas.core.arrays._mixins import NDArrayBackedExtensionArray
 from pandas.core.construction import (
     ensure_wrapped_if_datetimelike,
@@ -1343,11 +1347,15 @@ def column_setitem(
         intermediate Series at the DataFrame level (`s = df[loc]; s[idx] = value`)
         """
         if warn_copy_on_write() and not self._has_no_reference(loc):
-            warnings.warn(
-                COW_WARNING_GENERAL_MSG,
-                FutureWarning,
-                stacklevel=find_stack_level(),
-            )
+            if not isinstance(
+                self.blocks[self.blknos[loc]].values,
+                (ArrowExtensionArray, ArrowStringArray),
+            ):
+                warnings.warn(
+                    COW_WARNING_GENERAL_MSG,
+                    FutureWarning,
+                    stacklevel=find_stack_level(),
+                )
         elif using_copy_on_write() and not self._has_no_reference(loc):
             blkno = self.blknos[loc]
             # Split blocks to only copy the column we want to modify

pandas/tests/copy_view/test_interp_fillna.py

@@ -344,8 +344,9 @@ def test_fillna_inplace_ea_noop_shares_memory(
         assert not df._mgr._has_no_reference(1)
         assert not view._mgr._has_no_reference(1)
 
-    # TODO(CoW-warn) should this warn for ArrowDtype?
-    with tm.assert_cow_warning(warn_copy_on_write):
+    with tm.assert_cow_warning(
+        warn_copy_on_write and "pyarrow" not in any_numeric_ea_and_arrow_dtype
+    ):
         df.iloc[0, 1] = 100
     if isinstance(df["a"].dtype, ArrowDtype) or using_copy_on_write:
         tm.assert_frame_equal(df_orig, view)