This happens if the main server process was forcibly killed, e.g. by the kill command on Linux, or taskkill/TaskManager on Windows.
Previously, the process would stick around as a zombie, which messed up terminals in some cases (e.g. git bash), though even having zombies with no side effects is bad enough.
This reverts commit cbe0f44c4f7bc3715acbf148f981bd93111c4c8f.
This achieves the same result as the reverted commit wrt. process in the
same manner (writing a keepalive into the socket and checking if it
failed to send). However, it does _not_ allow the process to die on
reaching pipe EOF, since this can cause many spams of subprocesses when
stdin is actually not a tty (e.g. in a Docker container).
these weren't getting corrected since php-cs-fixer 3.0 due to a change in the default configuration for native_function_invocation. Since the builds are randomly choosing to use php-cs-fixer 2.19 at the moment, the consistency is a problem.
this happens if the parent process is killed via SIGINT, because its stdin will be closed, interrupting a blocking read. This might also happen if the user pressed CTRL+D, so we don't die unless end of socket stream was also detected.
closes#4335
