Error while using FilesystemIterator

How is $uri null here? The relevant specs appear to only permit a string value. PHPStan alerts similar with warning "Call to function is_null() with string will always evaluate to false."

This implies there is a bug somewhere else in the stack that needs to be identified and resolved, setting back to needs work to identify the root fault and for eventual tests to be included with the fix.

@see https://www.php.net/manual/en/streamwrapper.dir-opendir.php
@see Drupal\Core\StreamWrapper\PhpStreamWrapperInterface

It might be true the bug is somewhere else (although after few hours I couldn't find it), but have a look at core dir_opendir method signature here: https://git.drupalcode.org/project/drupal/-/blob/11.x/core/lib/Drupal/Co...
Although the comment says it's going to be a string, the method signature does not have the type enforcing.

Any hint on debugging this would be helpful

Any hint on debugging this would be helpful

I would suggest starting with xdebug and a conditional breakpoint for when $uri is null.

I suspect we will find this is likely a child call where the stack will show a parent call somewhere else in the streamWrapper code is passing NULL. I am not expecting this will be an issue in PHP proper, although if the stack trace stops with just the dir_opendir() call that could be a possibility.

Had a moments to run the steps to reproduce through Drush:

$ ddev drush --xdebug php
Psy Shell v0.12.7 (PHP 8.3.14 — cli) by Justin Hileman
s3fs test site (Drupal 11.1.0)
> $iterator = new \FilesystemIterator('s3://');
= FilesystemIterator {#8904
    path: "s3:/",
    filename: "2024-12",
    basename: "2024-12",
    pathname: "s3://2024-12",
    extension: "",
    realPath: false,
    aTime: 1969-12-31 16:00:00,
    mTime: 1969-12-31 16:00:00,
    cTime: 1969-12-31 16:00:00,
    inode: 0,
    size: 0,
    perms: 040777,
    owner: 0,
    group: 0,
    type: "dir",
    writable: true,
    readable: true,
    executable: true,
    file: false,
    dir: true,
    link: false,
  }

> $iterator->rewind()

   TypeError  Drupal\s3fs\StreamWrapper\S3fsStream::resolvePath(): Argument #1 ($path) must be of type string, null given, called in modules/custom/s3fs/src/StreamWrapper/S3fsStream.php on line 1123.

Here is the relevant portion of the stack trace:

S3fsStream.php:1123, Drupal\s3fs\StreamWrapper\S3fsStream->dir_opendir()
StreamWrapper.php:477, Aws\S3\StreamWrapper->Aws\S3\{closure:/var/www/html/vendor/aws/aws-sdk-php/src/S3/ StreamWrapper.php:475-479}()
StreamWrapper.php:941, Aws\S3\StreamWrapper->boolCall()
StreamWrapper.php:475, Aws\S3\StreamWrapper->dir_rewinddir()
35:1, FilesystemIterator->rewind()

The parent AWS's code is passing $this->openedPath as null. We intentional don't call parent::dir_opendir() in our dir_opendir() where it would be set. I don't believe we would want to use parent::opendir() as we depend upon the database. This is a private variable so we can't just set it in our dir_opendir().

Above stack should be enough to determine a proper solution.

Cursory thoughts:
We likely need to implement dir_rewinddir() ourselves.