Inconsistent behaviour with AppendIterator and empty generators
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Description
Description
I've encountered inconsistent behaviour in the handling of empty generators with AppendIterator. Please can you confirm whether this is a bug or some weird expected behaviour.
Scenario 1
When iterating over a generator that yields nothing, foreach has no items to iterate over so var_dump isn't called, as expected.
<?php
function yieldEmpty()
{
yield from [];
}
foreach (yieldEmpty() as $item) {
var_dump($item);
}
Scenario 2
When attaching a generator yielding items and a generator yielding nothing and attaching both to an AppendIterator, foreach iterates over the items from the former and the three values are output, as expected.
<?php
function yieldRows()
{
yield from ['one', 'two', 'three'];
}
function yieldEmpty()
{
yield from [];
}
$iterator = new AppendIterator();
$iterator->append(yieldRows());
$iterator->append(yieldEmpty());
foreach ($iterator as $item) {
var_dump($item);
}
Outputs (as expected):
string(3) "one"
string(3) "two"
string(5) "three"
Scenario 3
When attaching ONLY a generator yielding nothing and attaching it to an AppendIterator, foreach unexpectedly fails with an exception.
<?php
function yieldEmpty()
{
yield from [];
}
$iterator = new AppendIterator();
$iterator->append(yieldEmpty());
foreach ($iterator as $item) {
var_dump($item);
}
Expected output (following on from scenario 1 and 2):
string(3) "one"
string(3) "two"
string(5) "three"
Actual output:
PHP Fatal error: Uncaught Exception: Cannot traverse an already closed generator in /Users/richard.coupland/test3.php:11
Stack trace:
#0 /Users/richard.coupland/test3.php(11): AppendIterator->rewind()
#1 {main}
thrown in /Users/richard.coupland/test3.php on line 11
Fatal error: Uncaught Exception: Cannot traverse an already closed generator in /Users/richard.coupland/test3.php:11
Stack trace:
#0 /Users/richard.coupland/test3.php(11): AppendIterator->rewind()
#1 {main}
thrown in /Users/richard.coupland/test3.php on line 11
PHP Version
8.2.7
Operating System
No response
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the three AppendIterator scenarios with the yieldEmpty and yieldRows generators on PHP 8.2.7, focusing on the failure during foreach and AppendIterator->rewind(). Determine whether the differing behavior is intentional or a bug, then add or update regression coverage so the empty-generator case has defined, passing behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- php
- Domain
- backend
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Active
- Clarity
- Mostly clear
- Newbie friendliness
- 55/100