fix(child-process): unexpected pane closing issue with nushell (#648)

* fix unexpected pane closing issue with nushell

nushell doesn't create a new process group when spawnning a process,
so all processes including the ones spwanned by us are in the same
foreground group. So if kernel will send signal to every member of this
group.

This patch fixes this issue by creating a new foreground process group
when spawnning a new terminal pane.

Fix #615

Signed-off-by: Tw <tw19881113@gmail.com>

* add comment about unsafe

Co-authored-by: Aram Drevekenin <aram@poor.dev>

zellij-server/src/os_input_output.rs

@@ -1,5 +1,6 @@
 use std::env;
 use std::os::unix::io::RawFd;
+use std::os::unix::process::CommandExt;
 use std::path::PathBuf;
 use std::process::{Child, Command};
 use std::sync::{Arc, Mutex};
@@ -102,10 +103,21 @@ fn handle_terminal(cmd: RunCommand, orig_termios: termios::Termios) -> (RawFd, P
                 let pid_secondary = match fork_pty_res.fork_result {
                     ForkResult::Parent { child } => child,
                     ForkResult::Child => {
-                        let child = Command::new(cmd.command)
-                            .args(&cmd.args)
-                            .spawn()
-                            .expect("failed to spawn");
+                        let child = unsafe {
+                            Command::new(cmd.command)
+                                .args(&cmd.args)
+                                .pre_exec(|| -> std::io::Result<()> {
+                                    // this is the "unsafe" part, for more details please see:
+                                    // https://doc.rust-lang.org/std/os/unix/process/trait.CommandExt.html#notes-and-safety
+                                    unistd::setpgid(Pid::from_raw(0), Pid::from_raw(0))
+                                        .expect("failed to create a new process group");
+                                    Ok(())
+                                })
+                                .spawn()
+                                .expect("failed to spawn")
+                        };
+                        unistd::tcsetpgrp(0, Pid::from_raw(child.id() as i32))
+                            .expect("faled to set child's forceground process group");
                         handle_command_exit(child);
                         ::std::process::exit(0);
                     }