Fix last checkpoint finding in filtered files with correct extension (#17072)

Co-authored-by: awaelchli <aedu.waelchli@gmail.com>

src/lightning/pytorch/CHANGELOG.md

@@ -47,6 +47,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed checks for local file protocol due to fsspec changes in 2023.10.0 ([#19023](https://github.com/Lightning-AI/lightning/pull/19023))
 
 
+- Fixed automatic detection of 'last.ckpt' files to respect the extension when filtering ([#17072](https://github.com/Lightning-AI/lightning/pull/17072))
+
+
 
 ## [2.1.2] - 2023-11-15
 

src/lightning/pytorch/callbacks/model_checkpoint.py

@@ -626,12 +626,13 @@ class ModelCheckpoint(Checkpoint):
     def _find_last_checkpoints(self, trainer: "pl.Trainer") -> Set[str]:
         # find all checkpoints in the folder
         ckpt_path = self.__resolve_ckpt_dir(trainer)
+        last_pattern = rf"^{self.CHECKPOINT_NAME_LAST}(-(\d+))?"
+
+        def _is_last(path: Path) -> bool:
+            return path.suffix == self.FILE_EXTENSION and bool(re.match(last_pattern, path.stem))
+
         if self._fs.exists(ckpt_path):
-            return {
-                os.path.normpath(p)
-                for p in self._fs.ls(ckpt_path, detail=False)
-                if self.CHECKPOINT_NAME_LAST in os.path.split(p)[1]
-            }
+            return {os.path.normpath(p) for p in self._fs.ls(ckpt_path, detail=False) if _is_last(Path(p))}
         return set()
 
     def __warn_if_dir_not_empty(self, dirpath: _PATH) -> None:

tests/tests_pytorch/checkpointing/test_model_checkpoint.py

@@ -1509,3 +1509,28 @@ def test_resume_and_old_checkpoint_files_remain(same_resume_folder, tmp_path):
     else:
         assert set(os.listdir(first)) == {"epoch=0-step=2.ckpt", "epoch=0-step=4.ckpt"}  # no files deleted
         assert set(os.listdir(second)) == {"epoch=0-step=6.ckpt", "epoch=0-step=8.ckpt"}
+
+
+@pytest.mark.parametrize(
+    ("name", "extension", "folder_contents", "expected"),
+    [
+        ("last", ".ckpt", {}, {}),
+        ("any", ".any", {}, {}),
+        ("last", ".ckpt", {"last"}, {}),
+        ("any", ".any", {"last"}, {}),
+        ("last", ".ckpt", {"last", "last.ckpt"}, {"last.ckpt"}),
+        ("other", ".pt", {"last", "last.pt", "other.pt"}, {"other.pt"}),
+        ("last", ".ckpt", {"log.txt", "last-v0.ckpt", "last-v1.ckpt"}, {"last-v0.ckpt", "last-v1.ckpt"}),
+        ("other", ".pt", {"log.txt", "last-v0.ckpt", "other-v0.pt", "other-v1.pt"}, {"other-v0.pt", "other-v1.pt"}),
+    ],
+)
+def test_find_last_checkpoints(name, extension, folder_contents, expected, tmp_path):
+    for file in folder_contents:
+        (tmp_path / file).touch()
+
+    trainer = Trainer()
+    callback = ModelCheckpoint(dirpath=tmp_path)
+    callback.CHECKPOINT_NAME_LAST = name
+    callback.FILE_EXTENSION = extension
+    files = callback._find_last_checkpoints(trainer)
+    assert files == {str(tmp_path / p) for p in expected}