Psalm: Template parameters are not resolved for implicit `getIterator()` call

[weirdan]

https://getpsalm.org/r/6512bf307d

<?php
  namespace NS;
  /**
   * @template TKey
   * @template TValue
   */
  interface ICollection extends \IteratorAggregate {
     /** @return \Traversable<TKey,TValue> */
     public function getIterator();
  }

  class Collection implements ICollection {
     /** @var array */
     private $data;
     public function __construct(array $data) {
       $this->data = $data;
     }
     /** @psalm-suppress LessSpecificImplementedReturnType */
     public function getIterator(): \Traversable {
       return new \ArrayIterator($this->data);
     }
  }
  /** @var ICollection<string, int> */
  $c = new Collection(["a" => 1]);

  foreach ($c as $k => $v) { atan($k); strlen($v); } // $k and $v are reported as TKey, TValue, (and mixed if any methods are called on them)
  foreach ($c->getIterator() as $k => $v) { atan($k); strlen($v); } // $k and $v resolved to string/int property

Expected: both loops result in $k/$v types inferred as string/int.
Actual: only loop with explicit getIterator() resolve $k/$v as expected. Implicit call in first loop reports variables as TKey/TValue, and mixed if any method calls are performed on them.

[weirdan]

Note: when I dropped the ICollection interface and moved template definitions to the Collection itself Psalm was able to infer both cases properly. So it might have something to do with inheritance.

[muglug]

Did this work before https://github.com/vimeo/psalm/commit/1d3e66c79818d1c022670bc8f299f48ffd85d998?

[weirdan]

It didn't, the output is the same with 80cd77832b0020f5acb0ede2653ff773c438dd79

[muglug]

Thanks for this!