Fix contructors when TZ is set

[stephanedelprat]

Thank you for Timecop, it really makes testing as thorough as can be!

The Problem:
When Timecop was active and new DateTime('2026-01-30', new DateTimeZone('UTC')) (or DateTimeImmutable) was called with a date, the time was incorrectly interpreted as in the default timezone (e.g., Europe/Paris) and then converted to UTC, resulting in 2026-01-29 23:00:00 UTC instead of the correct 2026-01-30 00:00:00 UTC.

The Fix (in timecop.c):
Modified the get_formatted_mock_time() function to temporarily set the default timezone to the provided timezone before calling strtotime(), then restore the original default timezone afterwards. This ensures date strings without explicit time information are correctly interpreted in the specified timezone. The fix also handles edge cases where offset-based timezones (like +00:00) are used, skipping the timezone switch for those since date_default_timezone_set() doesn't accept them.

Files Changed:

• timecop.c - Core fix in get_formatted_mock_time() function
• tests/issue_timezone_datetime.phpt - New test case for this fix

Note : the problem still exists when using offset-based timezones. (+3:00 etc.)

---

Minimal PHP test to see the problem:

<?php

echo "Default timezone: ".date_default_timezone_get();
echo "\n";

foreach ([true, false] as $activated) {
    if ($activated) {
        \Timecop::travel(new \DateTime());
    } else {
        \Timecop::return();
    }
    echo "Timecop active: ".($activated ? 'yes' : 'no')."\n";

    $dtStart = new DateTimeImmutable('2026-01-30 00:00:00', new DateTimeZone('UTC'));
    $dtStart2 = new DateTime('2026-01-30', new DateTimeZone('UTC'));

    echo $dtStart->format('Y-m-d H:i:s T')." (timestamp: ".$dtStart->getTimestamp().")\n";
    echo $dtStart2->format('Y-m-d H:i:s T')." (timestamp: ".$dtStart->getTimestamp().")\n";

    echo "\n";
}

Output :

Default timezone: Europe/Paris
Timecop active: yes
2026-01-29 23:00:00 UTC (timestamp: 1769727600)
2026-01-29 23:00:00 UTC (timestamp: 1769727600)

Timecop active: no
2026-01-30 00:00:00 UTC (timestamp: 1769731200)
2026-01-30 00:00:00 UTC (timestamp: 1769731200)

[cs278]

Makes sense to me - thanks!