Warn when deprecated settings are used (#6353)

* Warn when deprecated settings are used.

* Mention deprecation in docs.

* Refer to the right place in the documentation.

celery/app/log.py

@@ -9,12 +9,14 @@
 import logging
 import os
 import sys
+import warnings
 from logging.handlers import WatchedFileHandler
 
 from kombu.utils.encoding import set_default_encoding_file
 
 from celery import signals
 from celery._state import get_current_task
+from celery.exceptions import CDeprecationWarning, CPendingDeprecationWarning
 from celery.local import class_property
 from celery.platforms import isatty
 from celery.utils.log import (ColorFormatter, LoggingProxy, get_logger,
@@ -70,6 +72,9 @@ def setup(self, loglevel=None, logfile=None, redirect_stdouts=False,
             CELERY_LOG_LEVEL=str(loglevel) if loglevel else '',
             CELERY_LOG_FILE=str(logfile) if logfile else '',
         )
+        warnings.filterwarnings('always', category=CDeprecationWarning)
+        warnings.filterwarnings('always', category=CPendingDeprecationWarning)
+        logging.captureWarnings(True)
         return handled
 
     def redirect_stdouts(self, loglevel=None, name='celery.redirected'):

celery/app/utils.py

@@ -77,6 +77,11 @@ class Settings(ConfigurationView):
 
     """
 
+    def __init__(self, *args, deprecated_settings=None, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        self.deprecated_settings = deprecated_settings
+
     @property
     def broker_read_url(self):
         return (
@@ -190,6 +195,20 @@ def humanize(self, with_defaults=False, censored=True):
             f'{key}: {pretty(value, width=50)}'
             for key, value in self.table(with_defaults, censored).items())
 
+    def maybe_warn_deprecated_settings(self):
+        # TODO: Remove this method in Celery 6.0
+        if self.deprecated_settings:
+            from celery.utils import deprecated
+            from celery.app.defaults import _TO_NEW_KEY
+            for setting in self.deprecated_settings:
+                deprecated.warn(description=f'The {setting!r} setting',
+                                removal='6.0.0',
+                                alternative=f'Use the {_TO_NEW_KEY[setting]} instead')
+
+            return True
+
+        return False
+
 
 def _new_key_to_old(key, convert=_TO_OLD_KEY.get):
     return convert(key, key)
@@ -263,6 +282,7 @@ def detect_settings(conf, preconf=None, ignore_keys=None, prefix=None,
     return Settings(
         preconf, [conf, defaults],
         (_old_key_to_new, _new_key_to_old),
+        deprecated_settings=is_in_old,
         prefix=prefix,
     )
 

celery/apps/worker.py

@@ -140,6 +140,14 @@ def on_start(self):
         if not self._custom_logging and self.redirect_stdouts:
             app.log.redirect_stdouts(self.redirect_stdouts_level)
 
+        # TODO: Remove the following code in Celery 6.0
+        if app.conf.maybe_warn_deprecated_settings():
+            logger.warning(
+                "Please run `celery upgrade settings path/to/settings.py` "
+                "to avoid these warnings and to allow a smoother upgrade "
+                "to Celery 6.0."
+            )
+
     def emit_banner(self):
         # Dump configuration to screen so we have some basic information
         # for when users sends bug reports.

docs/userguide/configuration.rst

@@ -47,12 +47,14 @@ names, are the renaming of some prefixes, like ``celery_beat_`` to ``beat_``,
 ``celeryd_`` to ``worker_``, and most of the top level ``celery_`` settings
 have been moved into a new  ``task_`` prefix.
 
-.. note::
+.. warning::
+
+    Celery will still be able to read old configuration files until Celery 6.0.
+    Afterwards, support for the old configuration files will be removed.
+    We provide the ``celery upgrade`` command that should handle
+    plenty of cases (including :ref:`Django <latentcall-django-admonition>`).
 
-    Celery will still be able to read old configuration files, so
-    there's no rush in moving to the new settings format. Furthermore,
-    we provide the ``celery upgrade`` command that should handle plenty
-    of cases (including :ref:`Django <latentcall-django-admonition>`).
+    Please migrate to the new configuration scheme as soon as possible.
 
 
 ========================================== ==============================================

docs/whatsnew-5.0.rst

@@ -116,7 +116,7 @@ please do so now.
 We elected to extend the deprecation period until 6.0 since
 we did not loudly warn about using these deprecated settings.
 
-Please refer to the :ref:`migration guide <v400-upgrade-settings>` for instructions.
+Please refer to the :ref:`migration guide <conf-old-settings-map>` for instructions.
 
 Step 3: Read the important notes in this document
 -------------------------------------------------