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