Backport PR #54800 on branch 2.1.x (ExtensionArray.fillna: start with DeprecationWarning about added copy keyword) (#54812)

Backport PR #54800: ExtensionArray.fillna: start with DeprecationWarning about added copy keyword

Co-authored-by: Joris Van den Bossche <[email protected]>

Author: meeseeksmachine

pandas/core/internals/blocks.py

@@ -2015,7 +2015,7 @@ def fillna(
                     "need to implement this keyword or an exception will be "
                     "raised. In the interim, the keyword is ignored by "
                     f"{type(self.values).__name__}.",
-                    FutureWarning,
+                    DeprecationWarning,
                     stacklevel=find_stack_level(),
                 )
 

pandas/tests/extension/decimal/test_decimal.py

@@ -133,7 +133,7 @@ def test_arith_series_with_array(self, data, all_arithmetic_operators):
     def test_fillna_frame(self, data_missing):
         msg = "ExtensionArray.fillna added a 'copy' keyword"
         with tm.assert_produces_warning(
-            FutureWarning, match=msg, check_stacklevel=False
+            DeprecationWarning, match=msg, check_stacklevel=False
         ):
             super().test_fillna_frame(data_missing)
 
@@ -166,7 +166,7 @@ def test_fillna_no_op_returns_copy(self, data):
     def test_fillna_series(self, data_missing):
         msg = "ExtensionArray.fillna added a 'copy' keyword"
         with tm.assert_produces_warning(
-            FutureWarning, match=msg, check_stacklevel=False
+            DeprecationWarning, match=msg, check_stacklevel=False
         ):
             super().test_fillna_series(data_missing)
 
@@ -178,13 +178,13 @@ def test_fillna_series_method(self, data_missing, fillna_method):
             super().test_fillna_series_method(data_missing, fillna_method)
 
     def test_fillna_copy_frame(self, data_missing, using_copy_on_write):
-        warn = FutureWarning if not using_copy_on_write else None
+        warn = DeprecationWarning if not using_copy_on_write else None
         msg = "ExtensionArray.fillna added a 'copy' keyword"
         with tm.assert_produces_warning(warn, match=msg, check_stacklevel=False):
             super().test_fillna_copy_frame(data_missing)
 
     def test_fillna_copy_series(self, data_missing, using_copy_on_write):
-        warn = FutureWarning if not using_copy_on_write else None
+        warn = DeprecationWarning if not using_copy_on_write else None
         msg = "ExtensionArray.fillna added a 'copy' keyword"
         with tm.assert_produces_warning(warn, match=msg, check_stacklevel=False):
             super().test_fillna_copy_series(data_missing)