wp-admin/includes/class-wp-filesystem-ftpsockets.php:478Checks if resource is a directory.
$pathstringbool public function is_dir( $path ) { $cwd = $this->cwd(); if ( $this->chdir( $path ) ) { $this->chdir( $cwd ); return true; } return false; }Introduced in 2.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-admin/includes/class-wp-filesystem-ftpsockets.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.