Description:
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Under PHP 7.1, calling session_set_cookie_params with an active session will successfully change the cookie sent to the client, IF session_regenerate_id is called afterward.

In PHP 7.2, calling session_set_cookie_params with an active session emits a warning:

Warning:  session_set_cookie_params(): Cannot change session cookie parameters when session is active

Additionally, the cookie is _not_ changed.

I've seen this described as a change which merely emits warnings informing developers of patterns that never worked in the first place and just failed silently (for example, the comments on #75650), but in this case presumably the function is bailing out after printing the warning, and the actual behavior is changed.

I was unable to find any discussion of this change in the migration documentation for PHP 7.2.

Test script:
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session_start();
$params = session_get_cookie_params();
session_set_cookie_params(100, $params['path'], $params['domain'], $params['secure']);
session_regenerate_id();

// Under 7.1 this emits a Set-Cookie with the 100-second lifetime respected

// Under 7.2, it produces a warning and the Set-Cookie does not respect the new lifetime