gh-115809: Improve TimedRotatingFileHandler.getFilesToDelete() (GH-115812)

Improve algorithm for computing which rolled-over log files to delete
in logging.TimedRotatingFileHandler. It is now reliable for handlers
without namer and with arbitrary deterministic namer that leaves
the datetime part in the file name unmodified.

Lib/logging/handlers.py

@@ -232,19 +232,19 @@ class TimedRotatingFileHandler(BaseRotatingHandler):
         if self.when == 'S':
             self.interval = 1 # one second
             self.suffix = "%Y-%m-%d_%H-%M-%S"
-            self.extMatch = r"^\d{4}-\d{2}-\d{2}_\d{2}-\d{2}-\d{2}(\.\w+)?$"
+            extMatch = r"(?<!\d)\d{4}-\d{2}-\d{2}_\d{2}-\d{2}-\d{2}(?!\d)"
         elif self.when == 'M':
             self.interval = 60 # one minute
             self.suffix = "%Y-%m-%d_%H-%M"
-            self.extMatch = r"^\d{4}-\d{2}-\d{2}_\d{2}-\d{2}(\.\w+)?$"
+            extMatch = r"(?<!\d)\d{4}-\d{2}-\d{2}_\d{2}-\d{2}(?!\d)"
         elif self.when == 'H':
             self.interval = 60 * 60 # one hour
             self.suffix = "%Y-%m-%d_%H"
-            self.extMatch = r"^\d{4}-\d{2}-\d{2}_\d{2}(\.\w+)?$"
+            extMatch = r"(?<!\d)\d{4}-\d{2}-\d{2}_\d{2}(?!\d)"
         elif self.when == 'D' or self.when == 'MIDNIGHT':
             self.interval = 60 * 60 * 24 # one day
             self.suffix = "%Y-%m-%d"
-            self.extMatch = r"^\d{4}-\d{2}-\d{2}(\.\w+)?$"
+            extMatch = r"(?<!\d)\d{4}-\d{2}-\d{2}(?!\d)"
         elif self.when.startswith('W'):
             self.interval = 60 * 60 * 24 * 7 # one week
             if len(self.when) != 2:
@@ -253,11 +253,17 @@ class TimedRotatingFileHandler(BaseRotatingHandler):
                 raise ValueError("Invalid day specified for weekly rollover: %s" % self.when)
             self.dayOfWeek = int(self.when[1])
             self.suffix = "%Y-%m-%d"
-            self.extMatch = r"^\d{4}-\d{2}-\d{2}(\.\w+)?$"
+            extMatch = r"(?<!\d)\d{4}-\d{2}-\d{2}(?!\d)"
         else:
             raise ValueError("Invalid rollover interval specified: %s" % self.when)
 
-        self.extMatch = re.compile(self.extMatch, re.ASCII)
+        # extMatch is a pattern for matching a datetime suffix in a file name.
+        # After custom naming, it is no longer guaranteed to be separated by
+        # periods from other parts of the filename.  The lookup statements
+        # (?<!\d) and (?!\d) ensure that the datetime suffix (which itself
+        # starts and ends with digits) is not preceded or followed by digits.
+        # This reduces the number of false matches and improves performance.
+        self.extMatch = re.compile(extMatch, re.ASCII)
         self.interval = self.interval * interval # multiply by units requested
         # The following line added because the filename passed in could be a
         # path object (see Issue #27493), but self.baseFilename will be a string
@@ -376,31 +382,22 @@ class TimedRotatingFileHandler(BaseRotatingHandler):
             for fileName in fileNames:
                 if fileName[:plen] == prefix:
                     suffix = fileName[plen:]
-                    if self.extMatch.match(suffix):
+                    if self.extMatch.fullmatch(suffix):
                         result.append(os.path.join(dirName, fileName))
         else:
-            # See bpo-44753: Don't use the extension when computing the prefix.
-            n, e = os.path.splitext(baseName)
-            prefix = n + '.'
-            plen = len(prefix)
             for fileName in fileNames:
-                # Our files could be just about anything after custom naming, but
-                # likely candidates are of the form
-                # foo.log.DATETIME_SUFFIX or foo.DATETIME_SUFFIX.log
-                if (not fileName.startswith(baseName) and fileName.endswith(e) and
-                    len(fileName) > (plen + 1) and not fileName[plen+1].isdigit()):
-                    continue
+                # Our files could be just about anything after custom naming,
+                # but they should contain the datetime suffix.
+                # Try to find the datetime suffix in the file name and verify
+                # that the file name can be generated by this handler.
+                m = self.extMatch.search(fileName)
+                while m:
+                    dfn = self.namer(self.baseFilename + "." + m[0])
+                    if os.path.basename(dfn) == fileName:
+                        result.append(os.path.join(dirName, fileName))
+                        break
+                    m = self.extMatch.search(fileName, m.start() + 1)
 
-                if fileName[:plen] == prefix:
-                    suffix = fileName[plen:]
-                    # See bpo-45628: The date/time suffix could be anywhere in the
-                    # filename
-
-                    parts = suffix.split('.')
-                    for part in parts:
-                        if self.extMatch.match(part):
-                            result.append(os.path.join(dirName, fileName))
-                            break
         if len(result) < self.backupCount:
             result = []
         else: