reloader ignores file open events

CHANGES.rst

@@ -24,6 +24,8 @@ Unreleased
 -   The reloader can pick up arguments to ``python`` like ``-X dev``, and does not
     require heuristics to determine how to reload the command. Only available
     on Python >= 3.10. :issue:`2589`
+-   The Watchdog reloader ignores file opened events. Bump the minimum version of
+    Watchdog to 2.3.0. :issue:`2603`
 
 
 Version 2.2.3

pyproject.toml

@@ -32,7 +32,7 @@ Twitter = "https://twitter.com/PalletsTeam"
 Chat = "https://discord.gg/pallets"
 
 [project.optional-dependencies]
-watchdog = ["watchdog"]
+watchdog = ["watchdog>=2.3"]
 
 [build-system]
 requires = ["setuptools"]

requirements/tests.txt

@@ -40,5 +40,5 @@ pytest-xprocess==0.22.2
     # via -r requirements/tests.in
 tomli==2.0.1
     # via pytest
-watchdog==2.2.1
+watchdog==2.3.1
     # via -r requirements/tests.in

requirements/typing.txt

@@ -21,5 +21,5 @@ types-setuptools==67.3.0.1
     # via -r requirements/typing.in
 typing-extensions==4.5.0
     # via mypy
-watchdog==2.2.1
+watchdog==2.3.1
     # via -r requirements/typing.in

src/werkzeug/_reloader.py

@@ -310,12 +310,17 @@ class WatchdogReloaderLoop(ReloaderLoop):
     def __init__(self, *args: t.Any, **kwargs: t.Any) -> None:
         from watchdog.observers import Observer
         from watchdog.events import PatternMatchingEventHandler
+        from watchdog.events import EVENT_TYPE_OPENED
+        from watchdog.events import FileModifiedEvent
 
         super().__init__(*args, **kwargs)
         trigger_reload = self.trigger_reload
 
         class EventHandler(PatternMatchingEventHandler):
-            def on_any_event(self, event):  # type: ignore
+            def on_any_event(self, event: FileModifiedEvent):  # type: ignore
+                if event.event_type == EVENT_TYPE_OPENED:
+                    return
+
                 trigger_reload(event.src_path)
 
         reloader_name = Observer.__name__.lower()

tests/test_serving.py

@@ -7,13 +7,18 @@
 import sys
 from io import BytesIO
 from pathlib import Path
+from unittest.mock import patch
 
 import pytest
+from watchdog.events import EVENT_TYPE_MODIFIED
+from watchdog.events import EVENT_TYPE_OPENED
+from watchdog.events import FileModifiedEvent
 
 from werkzeug import run_simple
 from werkzeug._reloader import _find_stat_paths
 from werkzeug._reloader import _find_watchdog_paths
 from werkzeug._reloader import _get_args_for_reloading
+from werkzeug._reloader import WatchdogReloaderLoop
 from werkzeug.datastructures import FileStorage
 from werkzeug.serving import make_ssl_devcert
 from werkzeug.test import stream_encode_multipart
@@ -115,6 +120,22 @@ def test_reloader_sys_path(tmp_path, dev_server, reloader_type):
     assert client.request().status == 200
 
 
+@patch.object(WatchdogReloaderLoop, "trigger_reload")
+def test_watchdog_reloader_ignores_opened(mock_trigger_reload):
+    reloader = WatchdogReloaderLoop()
+    modified_event = FileModifiedEvent("")
+    modified_event.event_type = EVENT_TYPE_MODIFIED
+    reloader.event_handler.on_any_event(modified_event)
+    mock_trigger_reload.assert_called_once()
+
+    reloader.trigger_reload.reset_mock()
+
+    opened_event = FileModifiedEvent("")
+    opened_event.event_type = EVENT_TYPE_OPENED
+    reloader.event_handler.on_any_event(opened_event)
+    reloader.trigger_reload.assert_not_called()
+
+
 @pytest.mark.skipif(sys.version_info >= (3, 10), reason="not needed on >= 3.10")
 def test_windows_get_args_for_reloading(monkeypatch, tmp_path):
     argv = [str(tmp_path / "test.exe"), "run"]