Fix bug in pin_versions_prune for days arg

pins/boards.py

@@ -473,7 +473,8 @@ def pin_versions_prune(self, name, n: "int | None" = None, days: "int | None" =
                 raise ValueError("Argument days is {days}, but must be greater than 0.")
 
             date_cutoff = datetime.today() - timedelta(days=days)
-            to_delete = [v for v in versions if v.created < date_cutoff]
+            # Avoid deleting the most recent version
+            to_delete = [v for v in versions[:-1] if v.created < date_cutoff]
 
         # message user about deletions ----
         # TODO(question): how to pin_inform? Log or warning?

pins/tests/test_boards.py

@@ -437,6 +437,33 @@ def test_board_pin_versions_prune_days(board, pin_prune, pin_name, days):
     assert len(new_versions) == days
 
 
+def test_board_pin_versions_prune_days_protect_most_recent(board, pin_name):
+    """To address https://github.com/rstudio/pins-python/issues/297"""
+    # RStudio cannot handle days, since it involves pulling metadata
+    if board.fs.protocol == "rsc":
+        with pytest.raises(NotImplementedError):
+            board.pin_versions_prune(pin_name, days=5)
+        return
+
+    today = datetime.now()
+    two_days_ago = today - timedelta(days=2, minutes=1)
+    three_days_ago = today - timedelta(days=3, minutes=1)
+
+    # Note, we are _not_ going to write a pin for today, otherwise we wouldn't be
+    # properly testing the protection of the most recent version - it would be trivially
+    # protected because it would always lie in the last day / fraction of a day.
+    board.pin_write({"a": 1}, pin_name, type="json", created=two_days_ago)
+    assert len(board.pin_versions(pin_name, as_df=False)) == 1
+    board.pin_write({"a": 2}, pin_name, type="json", created=three_days_ago)
+
+    # prune the versions, keeping only the most recent
+    board.pin_versions_prune(pin_name, days=1)
+
+    # check that only the most recent version remains
+    versions = board.pin_versions(pin_name, as_df=False)
+    assert len(versions) == 1
+
+
 # pin_search ==================================================================