Bootstrap 4 navigation accounting for Blade in Sage 9

controller.php

<?php

namespace App;

// Add to functions, or to a dedicated controllers file
// Needs a global body class to hook into

/**
 * Navigation arguments
 *
 * @param $data
 *
 * @return mixed
 */
function navControl( $data ) {

    // Pass the walker class to a var, so it
    // doesn't instantiate here.
    $bootstrapWalker = 'wp_bootstrap_navwalker';

    // Main Nav
    $mainNavArgs = [
        'theme_location' => 'primary_navigation',
        'walker'         => new $bootstrapWalker,
        'menu_class'     => 'navbar-nav mr-auto'
    ];

    $data['mainNavArgs'] = $mainNavArgs;

    return $data;

}

add_filter( 'sage/template/global/data', 'App\\navControl' );

header.blade.php

<nav class="navbar navbar-toggleable-md navbar-light bg-faded">

  <button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse"
          data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false"
          aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>

  <a class="navbar-brand" href="{{ home_url('/') }}">{{ get_bloginfo('name', 'display') }}</a>

  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    @if (has_nav_menu('primary_navigation'))
      {!! wp_nav_menu($mainNavArgs) !!}
    @endif
  </div>
</nav>

helper.php

<?php 

// In helpers.php, or whereveer makes the most sense to you

/*
 * Add global body class to hook our data up to
 */

add_filter( 'body_class', function( $classes ) {
    return array_merge( $classes, array( 'global' ) );
} );