I looked for the reason why loading a simple page is extremely slow (more than 15s) when the Symfony toolbar is active and Xdebug is activated in step-by-step mode (xdebug.mode=debug).
This happens from the moment Xdebug is enabled on the browser, regardless of whether listening is enabled on the IDE.
It turns out that the Symfony toolbar is loaded using an XHR request which contains the parameter XDEBUG_IGNORE=1 in order to avoid Xdebug slowing down its loading, but this is only taken into account from the version 3.4.0alpha1 of Xdebug which was released on May 31, 2024 (https://xdebug.org/updates).
At the time of writing, there is no stable version of Xdebug that contains this patch, since the latest version available is 3.4.0beta1 was released on October 4, 2024.
With Xdebug >= 3.4.0alpha1, we go from >=15s to around 200ms to load a basic page with the Symfony toolbar active, which is still much more comfortable and efficient for development.
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