These changes add consistent behavior when converting expired cookies back and forth from string representation intoSymfony\Component\HttpFoundation\Cookie instances inCookie::fromString:

• WhenMax-Age is zero andexpires is in the past, theexpires date is kept as is (previous behavior:expires is overwritten with current timestamp because it is reset to current timestamp +Max-Age)
• WhenMax-Age is zero andexpires is in the future, expires is reset to current timestamp, asMax-Age is the preferred "source of truth" (same as previous behavior)
• Add tests for how the Cookie class handlesMax-Age in a cookie string and howexpires andMax-Age interact
• Extract helper functionexpiresTimestamp so converting to a unix timestamp can be reused inCookie::fromString

This is more a new feature than a bug fix in my mind, therefore I would include it in 5.1+.