This function is in plugin.php file in wordpress core. I read the code and didn't get quietly what does it do. Can anyone give some explanation for this function?
Sometimes the easiest way is to go to docs...
Attempts activation of plugin in a "sandbox" and redirects on success.
A plugin that is already activated will not attempt to be activated again.
The way it works is by setting the redirection to the error before trying to include the plugin file. If the plugin fails, then the redirection will not be overwritten with the success message. Also, the options will not be updated and the activation hook will not be called on plugin error.
It should be noted that in no way the below code will actually prevent errors within the file. The code should not be used elsewhere to replicate the "sandbox", which uses redirection to work.
If any errors are found or text is outputted, then it will be captured to ensure that the success redirection will update the error redirection.