"Invalid installation files detected" message may be confusing

The message "Invalid installation files detected, upgrade cannot continue", is not helpful as it includes no indication of which files are blocking the upgrade.

To reproduce the problem

• add a file at /admin/generator.php
• decrement Moodle version number in database

  UPDATE mdl_config SET value=(value-1) WHERE name='version'

• log in to Moodle as admin to initiate upgrade process
• notice that upgrade "Invalid installation files detected" message does not include any indication of which files are blocking the upgrade.

The following modifications will report a list of files and folders that are blocking the upgrade and allow the server admin to take remedial action:

lib/upgradelib

• around line 319
• upgrade_stale_php_files_present()
• return an array of stale files or false

  upgrade_stale_php_files_present() in lib/upgradelib.php
  function upgrade_stale_php_files_present() {
  global $CFG;
  $files = array();
  $someexamplesofremovedfiles = array(
  /* list of files goes here */
  );
  foreach ($someexamplesofremovedfiles as $file) {
  if (file_exists($CFG->dirroot.$file)) {
  $files[] = $file;
  }
  }
  if (count($files)) {
  return $files;
  } else {
  return false;
  }
  }

admin/renderer.php

• around line 66
• upgrade_stale_php_files_page() method
• optionally accept and display an array of file/folder paths

  upgrade_stale_php_files_page() in admin/renderer.php
  public function upgrade_stale_php_files_page($files = false) {
  /* start output as before */
  $output .= get_string('upgradestalefilesinfo', 'admin', get_docs_url('Upgrading'));
  if ($files) {
  $output .= html_writer::start_tag('ul');
  foreach ($files as $file) {
  $output .= html_writer::tag('li', $file);
  }
  $output .= html_writer::end_tag('ul');
  } else {
  $output .= html_writer::empty_tag('br');
  }
  /* finish output as before */
  }

admin/index.php

• around line 203
• pass list of stale files from upgrade_stale_php_files_present() to $output->upgrade_stale_php_files_page($files)

  admin/index.php
  if ($files = upgrade_stale_php_files_present()) {
  $PAGE->set_title($stradministration);
  $PAGE->set_cacheable(false);
  $output = $PAGE->get_renderer('core', 'admin');
  echo $output->upgrade_stale_php_files_page($files);
  die();
  }