Fix GH-15375: nested "yield from" skips items after valid()/next()

[iliaal]

Nested yield from drops the inner generator's current value on the second and later delegations when it was primed via valid()/next(). The ZEND_GENERATOR_DO_INIT guard in zend_generator_resume() reads the flag on orig_generator, but in a nested chain the fresh delegation is established by the middle generator, whose flag it never checks. Track and check the delegating generator instead.

Fixes #15375

[arnaud-lb]

This looks right to me!

[kocsismate]

Is it possible that this commit broke the symfony demo app? if you have a look at the nightly benchmark logs (https://github.com/php/php-src/actions/runs/31758646923/job/94639986302#step:16:20969), it will be visible that the end of the HTML is duplicated for some reason:

aws_instance.host (remote-exec):                 <!-- Page rendered on August 14, 2026 at 1:00:17 AM UTC -->
aws_instance.host (remote-exec):     </body>
aws_instance.host (remote-exec): </html>
aws_instance.host (remote-exec):  -->
aws_instance.host (remote-exec):     </body>
aws_instance.host (remote-exec): </html>

even though the template properly has them: https://github.com/symfony/demo/blob/v2.8.0/templates/base.html.twig#L140

I "bisected" the PHP commits one by one and this was the first commit where the benchmark broke.

[iliaal]

Yes. Same as #23301: Twig's trailing yield from [] re-emits the last chunk ( --> / </html>). #23302.

[kocsismate]

Is it possible to revert this change until the fix is merged?

[LamentXU123]

If there is a real-world impact (in fact there is) we should revert this and apply #23302

[iliaal]

Is it possible to revert this change until the fix is merged?

I reviewed the #23302 PR and it looks correct and is pretty trivial (1 line fix) which can be safely merged imho, if we don't merge in the next few days, then I'd say reverting this change is the way to go...