[PHP-BUG] Bug #70904 [NEW]: `yield from` incorrectly marks valid generator as finished

From:             srice at fb dot com
Operating system: Linux
PHP version:      7.0.0RC7
Package:          PHP Language Specification
Bug Type:         Bug
Bug description:`yield from` incorrectly marks valid generator as finished

Description:
------------
The current implementation of the valid method doesnt properly take into
account the possibility that the inner generator could be executed
outside of the context of the outer generator. In this case, its saying
that the outer generator isnt valid because the inner generator isnt
valid, but in fact the outer generator still has more to execute.

Test script:
---------------
<?php

function g1() {
  yield 1;
  yield 2;
}

function g2($g1) {
  yield from $g1;
  echo "!\n";
  yield 3;
}

$g1 = g1();
$g2 = g2($g1);

while ($g2->valid()) {
  var_dump($g2->current());
  $g1->next();
}

Expected result:
----------------
I would expect the following:

int(1)
int(2)
NULL
NULL
NULL
...(infinite loop)

I say this because g2 got primed to the yield from statement, so it
should be returning for current whatever g1 is returning for current.
For a finished generator, this would be NULL.

Actual result:
--------------
int(1)
int(2)

-- 
Edit bug report at https://bugs.php.net/bug.php?id=70904&edit=1
-- 
Try a snapshot (PHP 5.4):   https://bugs.php.net/fix.php?id=70904&r=trysnapshot54
Try a snapshot (PHP 5.5):   https://bugs.php.net/fix.php?id=70904&r=trysnapshot55
Try a snapshot (trunk):     https://bugs.php.net/fix.php?id=70904&r=trysnapshottrunk
Fixed in SVN:               https://bugs.php.net/fix.php?id=70904&r=fixed
Fixed in release:           https://bugs.php.net/fix.php?id=70904&r=alreadyfixed
Need backtrace:             https://bugs.php.net/fix.php?id=70904&r=needtrace
Need Reproduce Script:      https://bugs.php.net/fix.php?id=70904&r=needscript
Try newer version:          https://bugs.php.net/fix.php?id=70904&r=oldversion
Not developer issue:        https://bugs.php.net/fix.php?id=70904&r=support
Expected behavior:          https://bugs.php.net/fix.php?id=70904&r=notwrong
Not enough info:            https://bugs.php.net/fix.php?id=70904&r=notenoughinfo
Submitted twice:            https://bugs.php.net/fix.php?id=70904&r=submittedtwice
register_globals:           https://bugs.php.net/fix.php?id=70904&r=globals
PHP 4 support discontinued: https://bugs.php.net/fix.php?id=70904&r=php4
Daylight Savings:           https://bugs.php.net/fix.php?id=70904&r=dst
IIS Stability:              https://bugs.php.net/fix.php?id=70904&r=isapi
Install GNU Sed:            https://bugs.php.net/fix.php?id=70904&r=gnused
Floating point limitations: https://bugs.php.net/fix.php?id=70904&r=float
No Zend Extensions:         https://bugs.php.net/fix.php?id=70904&r=nozend
MySQL Configuration Error:  https://bugs.php.net/fix.php?id=70904&r=mysqlcfg