Do not read the day as a two-digit year after the year position

[serhii73]

Fixes #519 (Close #519 is in the commit message).

Root cause

_parser.parse_number() tries the numeric directives in the resolved DATE_ORDER. For year-first orders (e.g. YMD, which the Japanese locale uses), the %y directive is tried first for every token, so any two-digit number that appears after the month is consumed as a year. In 4月20日 18:10 the 20 became the year 2020, the day was never parsed, and it was silently filled from the current date:

>>> dateparser.parse("4月20日 18:10")  # reported on 2019-04-20
datetime.datetime(2020, 4, 20, 18, 10)  # expected 2019-04-20 18:10

The bug is locale-independent — the same happens for dateparser.parse("4-20 18:10", settings={"DATE_ORDER": "YMD"}).

Fix

If a component that the date order places after the year has already been found, the year position in the date string has already been passed, so a two-digit number cannot be the year anymore. parse_number() now defers the %y directive in that case, reading the number as a two-digit year only if it cannot be any other component (so 4-99 still parses as April 1999, since 99 can be neither month nor day).

Year-last orders (DMY, MDY — the majority of locales) have no components after the year, so their behavior is unchanged by construction. Four-digit years (%Y) are never deferred.

Regression tests

test_two_digit_day_is_not_confused_with_year in tests/test_date_parser.py covers:

• 4月20日 18:10 and 3月8日 (ja) → day is the day, year comes from the reference date
• 4-20 18:10 with explicit DATE_ORDER: YMD → same, locale-independent
• 4-99 (YMD) → still April 1999 (two-digit year as last resort)
• 2020年4月20日 18:10 and 19年4月20日 → explicit years keep working

No existing tests were modified; the full suite passes (24103 passed, 18 skipped, 1 xfailed) and pre-commit (ruff, ruff-format) is clean.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.08%. Comparing base (315e396) to head (c0e1d4b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1358      +/-   ##
==========================================
+ Coverage   97.07%   97.08%   +0.01%     
==========================================
  Files         236      236              
  Lines        2975     2987      +12     
==========================================
+ Hits         2888     2900      +12     
  Misses         87       87              

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