Backport PR #59807: BUG (CoW): fix reference tracking in replace_list with None (#59943)

* BUG (CoW): fix reference tracking in replace_list with None (#59807)

(cherry picked from commit 3e8ac12)

* correct test to work without CoW

Author: jorisvandenbossche

pandas/core/internals/blocks.py

@@ -1218,7 +1218,7 @@ def _replace_coerce(
                     putmask_inplace(nb.values, mask, value)
                     return [nb]
                 if using_cow:
-                    return [self]
+                    return [self.copy(deep=False)]
                 return [self] if inplace else [self.copy()]
             return self.replace(
                 to_replace=to_replace,

pandas/tests/copy_view/test_replace.py

@@ -384,6 +384,15 @@ def test_replace_list_none(using_copy_on_write):
 
     assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
 
+    # replace multiple values that don't actually replace anything with None
+    # https://github.com/pandas-dev/pandas/issues/59770
+    df3 = df.replace(["d", "e", "f"], value=None)
+    tm.assert_frame_equal(df3, df_orig)
+    if using_copy_on_write:
+        assert tm.shares_memory(get_array(df, "a"), get_array(df3, "a"))
+    else:
+        assert not tm.shares_memory(get_array(df, "a"), get_array(df3, "a"))
+
 
 def test_replace_list_none_inplace_refs(using_copy_on_write, warn_copy_on_write):
     df = DataFrame({"a": ["a", "b", "c"]})