Create a shortcode in Roots 9.0. Source: https://discourse.roots.io/t/the-correct-way-to-add-shortcode/14394/4

functions.php

/**
 * Sage required files
 *
 * The mapped array determines the code library included in your theme.
 * Add or remove files to the array as needed. Supports child theme overrides.
 */
array_map(function ($file) use ($sage_error) {
    $file = "../app/{$file}.php";
    if (!locate_template($file, true, true)) {
        $sage_error(sprintf(__('Error locating <code>%s</code> for inclusion.', 'sage'), $file), 'File not found');
    }
}, ['helpers', 'setup', 'filters', 'admin', 'shortcodes']); //add shortcodes to the required files array

shortcodes.php

<?php
// app/shortocodes.php

namespace App;

use App\Controllers\App;

/**
 * Return if Shortcodes already exists.
 */
if (class_exists('Shortcodes')) {
    return;
}

/**
 * Shortcodes
 */
class Shortcodes
{
    /**
     * Constructor
     */
    public function __construct()
    {
        $shortcodes = [
            'calendario'
        ];

        return collect($shortcodes)
            ->map(function ($shortcode) {
                return add_shortcode($shortcode, [$this, strtr($shortcode, ['-' => '_'])]);
            });
    }

    /**
     * Calendar
     * Loads the calendar event partial
     *
     * @param  array  $atts
     * @param  string $content
     * @return string
     */
    public function calendario($atts, $content = null)
    {
        return \App\template('partials.eventos', array('shortcode' => 'true'));
    }

}

new Shortcodes();