Code like Hooks::run( 'WantedPages::getQueryInfo', [ &$this, &$query ] ); will trigger warnings in PHP 7.1. Ideally the solution would be to remove &, which hasn't been needed since PHP 4, however that breaks backwards-compatibility.
Instead, we can rename $this to a different variable, and then pass it by reference. Example:
// Avoid PHP 7.1 warning of passing $this by reference $editPage = $this; Hooks::run( 'EditPage::showEditForm:initial', [ &$editPage, &$out ] );
Example commit to fix this issue: https://gerrit.wikimedia.org/r/#/c/328387/