Global variable assigned by reference inside a file included in a function

Below is a simplified example of how a certain 3rd party module adds a 3rd party application into a page. The application is normally meant to be standalone and accessed directly, but the module uses a function to include the application at a specific URL.

module.php:

if ($path == 'some/specific/url') {
  load_app();
}

function load_app() {
  include('./app.php');
}

app.php:

// For this example, assume $_SESSION['a'] already exists as an array of strings.

global $b;

$b = &$_SESSION['a'];

do_something();

function do_something() {
  global $b;

  // Do something with $b.

  // Problem: $b is always NULL when it should be an array.
}

The problem is that the line $b = &$_SESSION['a']; in app.php doesn't seem to work properly so $GLOBALS['b'] remains NULL which means $b is also NULL inside do_something().

This appears to be because app.php is included from within a function in module.php, so I assume it's something to do with the scope of app.php and the assignment by reference.

Unfortunately, I can't modify app.php at all and I can't move the include() outside of the load_app() function in module.php, so is there any other way that module.php can be altered to make app.php work as it is supposed to?

Solution

After much trial and error with inserting global $b; in various places in an effort to propagate the global variable, what finally worked for me was the following:

module.php:

function load_app() {
  $GLOBALS['b'] = &$_SESSION['a'];
  include('./app.php');
}

It seems that assigning the reference directly to $GLOBALS['b'] in module.php allows app.php to work properly without any modifications. Assigning the reference to global $b does not.