fix: watch for file move with watchdog and Claude Code (#6798)

This pull request improves the file watching functionality to better
support editors that save files by moving temporary files into place,
such as Claude Code and some vim configurations.

Fixes ##6784

Author: mscolnick

marimo/_server/sessions.py

@@ -1199,6 +1199,11 @@ def _handle_file_change(
         # Get the latest codes
         codes = list(session.app_file_manager.app.cell_manager.codes())
         cell_ids = list(session.app_file_manager.app.cell_manager.cell_ids())
+
+        LOGGER.info(
+            f"File changed: {file_path}. num_cell_ids: {len(cell_ids)}, num_codes: {len(codes)}, changed_cell_ids: {changed_cell_ids}"
+        )
+
         # Send the updated cell ids and codes to the frontend
         session.write_operation(
             UpdateCellIdsRequest(cell_ids=cell_ids),

marimo/_utils/file_watcher.py

@@ -7,7 +7,7 @@
 from collections import defaultdict
 from collections.abc import Coroutine
 from pathlib import Path
-from typing import Any, Callable, Optional
+from typing import Callable, Optional
 
 from marimo import _loggers
 from marimo._dependencies.dependencies import DependencyManager
@@ -110,15 +110,36 @@ def __init__(
             self.loop = loop
             self.observer = watchdog.observers.Observer()
 
-        def on_modified(self, event: Any) -> None:
+        def on_modified(
+            self,
+            event: watchdog.events.FileModifiedEvent
+            | watchdog.events.DirModifiedEvent,
+        ) -> None:
             del event
             self.loop.create_task(self.on_file_changed())
 
+        def on_moved(
+            self,
+            event: watchdog.events.FileMovedEvent
+            | watchdog.events.DirMovedEvent,
+        ) -> None:
+            # Handle editors that save by creating a temp file and moving it
+            # (e.g., Claude Code, some vim configurations)
+            dest_path_str = (
+                event.dest_path
+                if isinstance(event.dest_path, str)
+                else event.dest_path.decode("utf-8")
+            )
+
+            if self.path == Path(dest_path_str):
+                self.loop.create_task(self.on_file_changed())
+
         def start(self) -> None:
             event_handler = watchdog.events.PatternMatchingEventHandler(  # type: ignore # noqa: E501
                 patterns=[str(self.path)]
             )
             event_handler.on_modified = self.on_modified  # type: ignore
+            event_handler.on_moved = self.on_moved  # type: ignore
             self.observer.schedule(  # type: ignore
                 event_handler,
                 str(self.path.parent),

tests/_server/test_sessions.py

@@ -15,8 +15,6 @@
 from typing import Any, Callable, TypeVar
 from unittest.mock import MagicMock
 
-import pytest
-
 from marimo._ast.app import App, InternalApp
 from marimo._ast.app_config import _AppConfig
 from marimo._config.manager import (
@@ -438,10 +436,6 @@ def test_session_with_kiosk_consumers() -> None:
     assert session.room.main_consumer is None
 
 
-@pytest.mark.skipif(
-    sys.version_info < (3, 10),
-    reason="This test is flaky on Python 3.9",
-)
 @save_and_restore_main
 async def test_session_manager_file_watching(tmp_path: Path) -> None:
     # Create a temporary file
@@ -659,10 +653,6 @@ def test_watch_mode_does_not_override_config(tmp_path: Path) -> None:
         session_manager_no_watch.shutdown()
 
 
-@pytest.mark.skipif(
-    sys.version_info < (3, 10),
-    reason="This test is flaky on Python 3.9",
-)
 @save_and_restore_main
 async def test_watch_mode_with_watcher_on_save_config() -> None:
     """Test that watch mode works correctly with watcher_on_save config."""
@@ -814,10 +804,6 @@ def __():
         os.remove(tmp_path)
 
 
-@pytest.mark.skipif(
-    sys.version_info < (3, 10),
-    reason="This test is flaky on Python 3.9",
-)
 @save_and_restore_main
 async def test_session_manager_file_rename() -> None:
     """Test that file renaming works correctly with file watching."""

tests/_utils/test_async_path.py

@@ -1,6 +1,5 @@
 import asyncio
 import os
-import sys
 import tempfile
 from pathlib import Path
 from unittest.mock import patch
@@ -416,10 +415,6 @@ async def test_operations_use_asyncio_to_thread(self):
 
 
 class TestAsyncPathEdgeCases:
-    @pytest.mark.skipif(
-        sys.version_info < (3, 10),
-        reason="Hardlink requires Python 3.10 or higher",
-    )
     async def test_hardlink_to(self):
         """Test hardlink_to creates hard link."""
         with tempfile.TemporaryDirectory() as tmp:
@@ -436,10 +431,6 @@ async def test_hardlink_to(self):
             target_stat = await target.stat()
             assert source_stat.st_ino == target_stat.st_ino
 
-    @pytest.mark.skipif(
-        sys.version_info < (3, 10),
-        reason="Hardlink requires Python 3.10 or higher",
-    )
     async def test_write_text_with_newline(self):
         """Test write_text with custom newline parameter."""
         with tempfile.TemporaryDirectory() as tmp:

tests/_utils/test_file_watcher.py

@@ -3,12 +3,13 @@
 
 import asyncio
 import os
-import sys
+import shutil
 from pathlib import Path
 from tempfile import NamedTemporaryFile
 
 import pytest
 
+from marimo._dependencies.dependencies import DependencyManager
 from marimo._utils.file_watcher import FileWatcherManager, PollingFileWatcher
 
 
@@ -45,10 +46,6 @@ async def test_callback(path: Path):
     assert callback_calls[0] == tmp_path
 
 
-@pytest.mark.skipif(
-    sys.version_info < (3, 10),
-    reason="File watcher tests require Python 3.10+",
-)
 async def test_file_watcher_manager() -> None:
     # Create two temporary files
     with (
@@ -151,3 +148,60 @@ async def callback3(path: Path) -> None:
         manager.stop_all()
         os.remove(tmp_path1)
         os.remove(tmp_path2)
+
+
+# This test is not working and watchdog makes CI hang in other areas
+# So we test this manually with `uv run --with=watchdog marimo edit nb.py --watch`
+@pytest.mark.xfail(reason="Test not working")
+@pytest.mark.skipif(
+    not DependencyManager.watchdog.has(),
+    reason="watchdog not installed",
+)
+async def test_watchdog_file_moved() -> None:
+    """Test that watchdog detects when a temp file is moved to the target path.
+
+    This simulates editors like Claude Code that save by creating a temp file
+    and then moving it to the target location.
+    """
+    from marimo._utils.file_watcher import _create_watchdog
+
+    with NamedTemporaryFile(delete=False) as tmp_file:
+        tmp_path = Path(tmp_file.name)
+        tmp_file.write(b"initial content")
+
+    callback_calls: list[Path] = []
+
+    async def test_callback(path: Path) -> None:
+        callback_calls.append(path)
+
+    try:
+        # Create watcher
+        loop = asyncio.get_event_loop()
+        watcher = _create_watchdog(tmp_path, test_callback, loop)
+        watcher.start()
+
+        # Wait for watcher to be ready
+        await asyncio.sleep(0.2)
+
+        # Simulate Claude Code save pattern: create temp file and move it
+        temp_save_path = tmp_path.parent / f"{tmp_path.name}.tmp.12345"
+        with open(temp_save_path, "w") as f:  # noqa: ASYNC230
+            f.write("modified content")
+
+        # Move temp file to target (simulating atomic save)
+        shutil.move(str(temp_save_path), str(tmp_path))
+
+        # Wait for the watcher to detect the move
+        await asyncio.sleep(0.3)
+
+        # Stop watcher
+        watcher.stop()
+
+        # Assert that the callback was called
+        assert len(callback_calls) >= 1
+        assert callback_calls[0] == tmp_path
+
+    finally:
+        # Cleanup
+        if tmp_path.exists():
+            os.remove(tmp_path)

tests/mocks.py

@@ -2,7 +2,6 @@
 
 import difflib
 import re
-import sys
 from html.parser import HTMLParser
 from pathlib import Path
 from typing import Callable
@@ -102,15 +101,6 @@ def write_result() -> None:
             )
 
             if result != expected:
-                # Old versions of markdown are allowed to have different
-                # tags and whitespace
-                if sys.version_info < (3, 10):
-                    if ToText.apply(result) == ToText.apply(expected):
-                        pytest.xfail(
-                            "Different tags in older markdown versions"
-                        )
-                        return
-
                 write_result()
                 print("Snapshot updated")