[dhrupo]

PHP 8.6 gives several DateTimeImmutable methods a tentative static return type. Safe\DateTimeImmutable overrides them with self, so loading the class on 8.6 emits nine deprecation notices, for example:

Return type of Safe\DateTimeImmutable::modify($modify): Safe\DateTimeImmutable should either be compatible with DateTimeImmutable::modify(string $modifier): static, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

This marks add(), sub(), modify(), setDate(), setISODate(), setTime(), setTimestamp(), setTimezone() and createFromInterface() with #[\ReturnTypeWillChange], as createFromMutable() and __set_state() already are.

The new test loads the class in a separate process and asserts no deprecation is raised. It fails on 8.6.0-dev without the change. The full suite passes on PHP 8.1 to 8.6.

[dhrupo]

The failing checks here are not caused by this branch: PHPStan fails the same way on a clean master.

Running the repo's own phpstan.neon on master at b713b22, with phpVersion set explicitly, gives:

phpVersion	errors on clean master
8.1	lib/DateTime.php 43, 55, 58, 75 + lib/DateTimeImmutable.php 99 (5)
8.3	lib/DateTime.php 43, 55, 58, 75 (4)
8.6	lib/DateTime.php 43, 58, 75 + lib/DateTimeImmutable.php 246 (4)

This branch produces the same set, with the lib/DateTimeImmutable.php line shifted by the nine lines it adds. master shows green only because the Tests workflow last ran there on 24 October; phpstan.neon sets no phpVersion, so each matrix job analyses as its own version.

Since the three lib/DateTime.php errors appear at 8.1, 8.3 and 8.6 alike, no pull request can turn this workflow green until that file is addressed. I have opened a separate issue for it rather than widen this change.

What this branch does fix, measured on 8.6.0-dev (built 24 October) by loading the class directly, so Composer's autoloader cannot resolve to another checkout:

	deprecations on load
Safe\DateTimeImmutable, master	18
Safe\DateTimeImmutable, this branch	0

Safe\DateTime emits none on 8.2, 8.3 or 8.6, so this is specific to the immutable class.

At phpVersion 8.1 it also removes the lib/DateTimeImmutable.php:99 PHPStan error (Safe\DateTimeImmutable::modify() not covariant with the tentative static(DateTimeImmutable)|false).

One note on createFromInterface(): PHPStan reports that one as method.childReturnType, which the attribute does not suppress, so it is still listed at 8.6. The attribute is required at runtime even so — removing just that one brings its deprecation back on 8.6. PHPStan's stubs and PHP disagree about whether that parent return type is tentative.