Add detection of invalid time format when too many "S" (#855)

CHANGELOG.rst

@@ -2,6 +2,7 @@
 =============
 
 - Add a new ``context`` optional argument to ``logger.add()`` specifying ``multiprocessing`` context (like ``"spawn"`` or ``"fork"``) to be used internally instead of the default one (`#851 <https://github.com/Delgan/loguru/issues/851>`_).
+- Raise ``ValueError`` if an attempt to use nanosecond precision for time formatting is detected (`#855 <https://github.com/Delgan/loguru/issues/855>`_).
 
 
 `0.7.0`_ (2023-04-10)

loguru/_datetime.py

@@ -4,9 +4,9 @@
 from datetime import timedelta, timezone
 from time import localtime, strftime
 
-tokens = r"H{1,2}|h{1,2}|m{1,2}|s{1,2}|S{1,6}|YYYY|YY|M{1,4}|D{1,4}|Z{1,2}|zz|A|X|x|E|Q|dddd|ddd|d"
+tokens = r"H{1,2}|h{1,2}|m{1,2}|s{1,2}|S+|YYYY|YY|M{1,4}|D{1,4}|Z{1,2}|zz|A|X|x|E|Q|dddd|ddd|d"
 
-pattern = re.compile(r"(?:{0})|\[(?:{0}|!UTC)\]".format(tokens))
+pattern = re.compile(r"(?:{0})|\[(?:{0}|!UTC|)\]".format(tokens))
 
 
 class datetime(datetime_):  # noqa: N801
@@ -23,6 +23,13 @@ def __format__(self, spec):
         if "%" in spec:
             return datetime_.__format__(dt, spec)
 
+        if "SSSSSSS" in spec:
+            raise ValueError(
+                "Invalid time format: the provided format string contains more than six successive "
+                "'S' characters. This may be due to an attempt to use nanosecond precision, which "
+                " not supported."
+            )
+
         year, month, day, hour, minute, second, weekday, yearday, _ = dt.timetuple()
         microsecond = dt.microsecond
         timestamp = dt.timestamp()

tests/test_datetime.py

@@ -82,7 +82,9 @@
         ("[YYYY] MM [DD]", "2018-02-03 11:09:00.000002", ("UTC", 0), "YYYY 02 DD"),
         ("[YYYY MM DD]", "2018-01-03 11:03:04.000002", ("UTC", 0), "[2018 01 03]"),
         ("[[YY]]", "2018-01-03 11:03:04.000002", ("UTC", 0), "[YY]"),
-        ("[]", "2018-01-03 11:03:04.000002", ("UTC", 0), "[]"),
+        ("[]", "2018-01-03 11:03:04.000002", ("UTC", 0), ""),
+        ("[[]]", "2018-01-03 11:03:04.000002", ("UTC", 0), "[]"),
+        ("SSSSSS[]SSS[]SSSSSS", "2018-01-03 11:03:04.100002", ("UTC", 0), "100002100100002"),
         ("[HHmmss", "2018-01-03 11:03:04.000002", ("UTC", 0), "[110304"),
         ("HHmmss]", "2018-01-03 11:03:04.000002", ("UTC", 0), "110304]"),
         ("HH:mm:ss!UTC", "2018-01-01 11:30:00.0", ("A", 7200), "09:30:00"),
@@ -153,3 +155,12 @@ def test_freezegun_mocking(writer):
         logger.info("Frozen")
 
     assert writer.read() == "[2000 01 01 18:00:05] Frozen\n"
+
+
+@pytest.mark.parametrize(
+    "format", ["ss.SSSSSSS", "SS.SSSSSSSS.SS", "HH:mm:ss.SSSSSSSSS", "SSSSSSSSSS"]
+)
+def test_invalid_time_format(writer, format):
+    logger.add(writer, format=f"{{time:{format}}} {{message}}", catch=False)
+    with pytest.raises(ValueError, match="Invalid time format"):
+        logger.info("Test")