Fix ParserError on subsecond precision beyond nanoseconds

src/pendulum/parsing/__init__.py

@@ -49,7 +49,7 @@
     # Subsecond part (optional)
     "    (?P<subsecondsection>"
     "        (?:[.|,])"  # Subsecond separator (optional)
-    r"        (?P<subsecond>\d{1,9})"  # Subsecond
+    r"        (?P<subsecond>\d+)"  # Subsecond (any number of digits; truncated to microseconds below)
     "    )?"
     ")?"
     "$",

src/pendulum/parsing/iso8601.py

@@ -49,7 +49,7 @@
     # Subsecond part (optional)
     "    (?P<subsecondsection>"
     "        (?:[.,])"  # Subsecond separator (optional)
-    r"        (?P<subsecond>\d{1,9})"  # Subsecond
+    r"        (?P<subsecond>\d+)"  # Subsecond (any number of digits; truncated to microseconds below)
     "    )?"
     # Timezone offset
     "    (?P<tz>"

tests/parsing/test_parse_iso8601.py

@@ -214,3 +214,18 @@ def test_parse_iso8601_duration_invalid():
     # Must include at least one element
     with pytest.raises(ValueError):
         parse_iso8601("P")
+
+
+def test_parse_iso8601_subsecond_beyond_nanoseconds_pure_python():
+    # Regression test for the pure-Python ISO 8601 parser (used as a fallback
+    # when the compiled extension is unavailable): a subsecond part longer
+    # than 9 digits used to raise a ParserError instead of being truncated to
+    # microsecond precision like `datetime.fromisoformat` does. Imported
+    # directly so the check runs regardless of whether the Rust extension is
+    # built, since `pendulum.parsing.parse_iso8601` prefers the extension
+    # when it's available.
+    from pendulum.parsing.iso8601 import parse_iso8601 as py_parse_iso8601
+
+    parsed = py_parse_iso8601("2016-10-06T12:34:56.1234567890123+05:30")
+
+    assert parsed == datetime(2016, 10, 6, 12, 34, 56, 123456, FixedTimezone(19800))

tests/parsing/test_parsing.py

@@ -156,6 +156,41 @@ def test_rfc_3339_extended_nanoseconds():
     assert parsed.utcoffset().total_seconds() == 19800
 
 
+def test_rfc_3339_extended_beyond_nanoseconds():
+    # A subsecond part longer than 9 digits (i.e. finer than nanoseconds) is
+    # unusual but not invalid ISO 8601: it should still be accepted and
+    # truncated to microsecond precision, the same as `datetime.fromisoformat`
+    # does, instead of raising a ParserError.
+    text = "2016-10-06T12:34:56.1234567890123+05:30"
+
+    parsed = parse(text)
+
+    assert parsed.year == 2016
+    assert parsed.month == 10
+    assert parsed.day == 6
+    assert parsed.hour == 12
+    assert parsed.minute == 34
+    assert parsed.second == 56
+    assert parsed.microsecond == 123456
+    assert parsed.utcoffset().total_seconds() == 19800
+
+
+def test_common_format_extended_beyond_nanoseconds():
+    # Same as `test_rfc_3339_extended_beyond_nanoseconds()` but for the
+    # "common" datetime format (handled separately from the ISO 8601 parser).
+    text = "2016/10/06 12:34:56.1234567890123"
+
+    parsed = parse(text)
+
+    assert parsed.year == 2016
+    assert parsed.month == 10
+    assert parsed.day == 6
+    assert parsed.hour == 12
+    assert parsed.minute == 34
+    assert parsed.second == 56
+    assert parsed.microsecond == 123456
+
+
 def test_iso_8601_date():
     text = "2012"