/**
     * Construct a user menu, returning HTML that can be echoed out by a
     * layout file.
     *
     * @param stdClass $user A user object, usually $USER.
     * @param bool $withlinks true if a dropdown should be built.
     * @return string HTML fragment.
     */
    public function user_menu($user = null, $withlinks = null) {
        global $USER, $CFG;
        require_once($CFG->dirroot . '/user/lib.php');

        if (is_null($user)) {
            $user = $USER;
        }

        // Note: this behaviour is intended to match that of core_renderer::login_info,
        // but should not be considered to be good practice; layout options are
        // intended to be theme-specific. Please don't copy this snippet anywhere else.
        if (is_null($withlinks)) {
            $withlinks = empty($this->page->layout_options['nologinlinks']);
        }

        // Add a class for when $withlinks is false.
        $usermenuclasses = 'usermenu';
        if (!$withlinks) {
            $usermenuclasses .= ' withoutlinks';
        }

        $returnstr = "";

        // If during initial install, return the empty return string.
        if (during_initial_install()) {
            return $returnstr;
        }

        $loginpage = $this->is_login_page();
        $loginurl = get_login_url();
        // If not logged in, show the typical not-logged-in string.
        if (!isloggedin()) {
            $returnstr = get_string('loggedinnot', 'moodle');
            if (!$loginpage) {
                $returnstr .= " (<a href=\"$loginurl\">" . get_string('login') . '</a>)';
            }
            return html_writer::div(
                html_writer::span(
                    $returnstr,
                    'login'
                ),
                $usermenuclasses
            );

        }

        // If logged in as a guest user, show a string to that effect.
        if (isguestuser()) {
            $returnstr = get_string('loggedinasguest');
            if (!$loginpage && $withlinks) {
                $returnstr .= " (<a href=\"$loginurl\">".get_string('login').'</a>)';
            }

            return html_writer::div(
                html_writer::span(
                    $returnstr,
                    'login'
                ),
                $usermenuclasses
            );
        }

        // Get some navigation opts.
        $opts = user_get_user_navigation_info($user, $this->page);

        $avatarclasses = "avatars";
        $avatarcontents = html_writer::span($opts->metadata['useravatar'], 'avatar current');
        $usertextcontents = $opts->metadata['userfullname'];

        // Other user.
        if (!empty($opts->metadata['asotheruser'])) {
            $avatarcontents .= html_writer::span(
                $opts->metadata['realuseravatar'],
                'avatar realuser'
            );
            $usertextcontents = $opts->metadata['realuserfullname'];
            $usertextcontents .= html_writer::tag(
                'span',
                get_string(
                    'loggedinas',
                    'moodle',
                    html_writer::span(
                        $opts->metadata['userfullname'],
                        'value'
                    )
                ),
                array('class' => 'meta viewingas')
            );
        }

        // Role.
        if (!empty($opts->metadata['asotherrole'])) {
//.........这里部分代码省略.........

 /**
  * Test setting the user menu avatar size.
  */
 public function test_user_menu_custom_avatar_size()
 {
     global $PAGE;
     $this->resetAfterTest(true);
     $testsize = 100;
     $user = $this->getDataGenerator()->create_user();
     $opts = user_get_user_navigation_info($user, $PAGE, array('avatarsize' => $testsize));
     $avatarhtml = $opts->metadata['useravatar'];
     $matches = [];
     preg_match('/(?:.*width=")(\\d*)(?:" height=")(\\d*)(?:".*\\/>)/', $avatarhtml, $matches);
     $this->assertCount(3, $matches);
     $this->assertEquals(intval($matches[1]), $testsize);
     $this->assertEquals(intval($matches[2]), $testsize);
 }