Bug #72692 [Com]: Bad behaviour of AppendIterator with Empty Generator

From: Date: Tue, 01 Jun 2021 13:11:57 +0000
Subject: Bug #72692 [Com]: Bad behaviour of AppendIterator with Empty Generator
References: 1  Groups: php.bugs 
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Edit report at https://bugs.php.net/bug.php?id=72692&edit=1

 ID:                 72692
 Comment by:         enumag at gmail dot com
 Reported by:        pierrick@php.net
 Summary:            Bad behaviour of AppendIterator with Empty Generator
 Status:             Open
 Type:               Bug
 Package:            SPL related
 PHP Version:        5.6.24
 Block user comment: N
 Private report:     N

 New Comment:

What's even worse is that this bug is quite hidden - if the empty generator is NOT the first
iterator in the AppendIterator then everything works fine. It only breaks if the empty generator is
first.

----

Test script:

<?php

function createGenerator(array $array): Generator
{
    yield from $array;
}

// Example 1 (works)

$iterator = new AppendIterator();
$iterator->append(createGenerator([1]));
$iterator->append(createGenerator([2]));
$iterator->append(createGenerator([]));
$iterator->append(createGenerator([3]));

foreach ($iterator as $value) {
    echo $value;
}

// Example 1 (fails)

$iterator = new AppendIterator();
$iterator->append(createGenerator([])); // <-- this line is new
$iterator->append(createGenerator([1]));
$iterator->append(createGenerator([2]));
$iterator->append(createGenerator([]));
$iterator->append(createGenerator([3]));

foreach ($iterator as $value) {
    echo $value;
}

----

Expected result:

123456

----

Actual result:

123
Fatal error: Uncaught Exception: Cannot traverse an already closed generator in /in/jRMa7:29
Stack trace:
#0 /in/jRMa7(29): AppendIterator->rewind()
#1 {main}
  thrown in /in/jRMa7 on line 29

Process exited with code 255.


Previous Comments:
------------------------------------------------------------------------
[2021-04-23 16:30:44] cmb@php.net

Related To: Bug #71436

------------------------------------------------------------------------
[2019-09-17 15:03:20] f dot bosch at genkgo dot nl

I hit this bug too today, still valid in PHP7.4. See https://3v4l.org/R4AH3. For others who hit this bug: use a closure
and yield from as alternative.

function createEmptyGen1() { if(false) { yield 1; } }
function createEmptyGen2() { if(false) { yield 2; } }

$ai = (function () {
    yield from createEmptyGen1();
    yield from createEmptyGen2();
})();

foreach ($ai as $_);

------------------------------------------------------------------------
[2016-07-28 23:59:57] nikic@php.net

Related: Bug #71436

------------------------------------------------------------------------
[2016-07-28 05:09:13] pierrick@php.net

Description:
------------
When giving an new empty generator, AppendIterator will directly throw an Exception "Cannot
traverse an already closed generator" even if the given generator is new.

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

function createEmptyGen() { if(false) { yield 1; } }
$gen = createEmptyGen();

$ai = new AppendIterator();
$ai->append($gen);
var_dump(iterator_to_array($gen));


Expected result:
----------------
array(0) {
}


Actual result:
--------------
Fatal error: Uncaught Exception: Cannot traverse an already closed generator in
/home/pierrick/php-src/github/foo.php:14
Stack trace:
#0 /home/pierrick/php-src/github/foo.php(14): iterator_to_array(Object(Generator))
#1 {main}
  thrown in /home/pierrick/php-src/github/foo.php on line 14



------------------------------------------------------------------------



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Edit this bug report at https://bugs.php.net/bug.php?id=72692&edit=1

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