drupal_phpstan_bootstrap.php

<?php

use Symfony\Component\HttpFoundation\Request;
use Drupal\Core\DrupalKernel;

$autoload = require __DIR__ . '/vendor/autoload.php';

$cwd = getcwd();
chdir('docroot');
$drupalKernel = DrupalKernel::createFromRequest(
  Request::createFromGlobals(),
  $autoload,
  'dev',
  true,
  __DIR__
);
$drupalKernel->boot();
$drupalKernel->getContainer()->get('module_handler')->loadAll();
chdir($cwd);

return $autoload;

phpstan.neon

parameters:
  bootstrap: ./drupal_phpstan_autoload.php
  ignoreErrors:
    - '#Function pager_.*#'
    - ... ignore some other errors here, not _all_ functions are registered in the bootstrap