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[cleanup] Deprecate tools.RotatingFileHandler

- use standard implementation of RotatingFileHandler
- use a namer method to create a filename from given baseFilename
  and counter
- give up logfilecount of -1 for infinite amount of backups; set it
  to 999 and deprecate their usage
- deprecate old usage in bot.py and _logging.py

Change-Id: I749a4cfc0c948f156650834a01f2e756af9b746e
---
M pywikibot/bot.py
M pywikibot/tools/_logging.py
2 files changed, 47 insertions(+), 8 deletions(-)

diff --git a/pywikibot/bot.py b/pywikibot/bot.py
index b261d09..1a9f9cb 100644
--- a/pywikibot/bot.py
+++ b/pywikibot/bot.py
@@ -130,6 +130,7 @@
     UnhandledAnswer,
 )
 from pywikibot.exceptions import (
+    ArgumentDeprecationWarning,
     EditConflictError,
     Error,
     LockedPageError,
@@ -167,9 +168,10 @@
     deprecated,
     deprecated_args,
     issue_deprecation_warning,
+    redirect_func,
     suppress_warnings,
 )
-from pywikibot.tools._logging import LoggingFormatter, RotatingFileHandler
+from pywikibot.tools._logging import LoggingFormatter
 from pywikibot.tools.formatter import color_format
 
 
@@ -291,6 +293,13 @@
 _handlers_initialized = False
 
 
+def handler_namer(name: str) -> str:
+    """Modify the filename of a log file when rotating."""
+    path, qualifier = name.rsplit('.', 1)
+    root, ext = os.path.splitext(path)
+    return '{}.{}{}'.format(root, qualifier, ext)
+
+
 def init_handlers(strm=None):
     """Initialize logging system for terminal-based bots.
 
@@ -382,10 +391,23 @@
             logfile = config.datafilepath('logs', '{}-{}bot.log'
                                           .format(module_name, pid))
 
-        file_handler = RotatingFileHandler(filename=logfile,
-                                           maxBytes=1024 * config.logfilesize,
-                                           backupCount=config.logfilecount,
-                                           encoding='utf-8')
+        # give up infinite rotating file handler with logfilecount of -1;
+        # set it to 999 and use the standard implementation
+        max_count = config.logfilecount
+        if max_count == -1:
+            max_count = 999
+            issue_deprecation_warning('config.logfilecount with value -1',
+                                      'any positive number',
+                                      warning_class=ArgumentDeprecationWarning,
+                                      since='6.5.0')
+
+        file_handler = logging.handlers.RotatingFileHandler(
+            filename=logfile,
+            maxBytes=config.logfilesize << 10,
+            backupCount=max_count,
+            encoding='utf-8'
+        )
+        file_handler.namer = handler_namer
 
         file_handler.setLevel(DEBUG)
         form = LoggingFormatter(
@@ -2262,6 +2284,10 @@
 
 set_interface(config.userinterface)
 
+# Deprecate RotatingFileHandler
+RotatingFileHandler = redirect_func(logging.handlers.RotatingFileHandler,
+                                    since='6.5.0')
+
 # NOTE: (T286348)
 # Do not use ModuleDeprecationWrapper with this module.
 # pywikibot.bot.ui would be wrapped through the ModuleDeprecationWrapper
diff --git a/pywikibot/tools/_logging.py b/pywikibot/tools/_logging.py
index c3b79df..830b8d9 100644
--- a/pywikibot/tools/_logging.py
+++ b/pywikibot/tools/_logging.py
@@ -7,11 +7,16 @@
 import logging
 import os
 
+from pywikibot.tools import ModuleDeprecationWrapper
 
-# Logging module configuration
-class RotatingFileHandler(logging.handlers.RotatingFileHandler):
 
-    """Modified RotatingFileHandler supporting unlimited amount of backups."""
+class _RotatingFileHandler(logging.handlers.RotatingFileHandler):
+
+    """DEPRECATED Modified RotatingFileHandler.
+
+    Use namer instead. See:
+    https://docs.python.org/3/howto/logging-cookbook.html#cookbook-rotator-namer
+    """
 
     def doRollover(self):
         """Modified naming system for logging files.
@@ -93,3 +98,11 @@
             record.args = (msg,)
 
         return super().format(record).rstrip()
+
+
+wrapper = ModuleDeprecationWrapper(__name__)
+wrapper.add_deprecated_attr(
+    'RotatingFileHandler', _RotatingFileHandler,
+    replacement_name=('logging.handlers.RotatingFileHandler '
+                      'with your own namer'),
+    since='6.5.0')

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