Trap Ctrl-C in the REPL: if no command is running clear the prompt, if some command is running ask for confirmation before exiting

[lihaoyi]

This ports over one of the other Ammonite features to the Scala 3 REPL, making it behave much more similarly to other prompt environment (Bash, Python, etc.):

• If there is no code running, Ctrl-C just resets the prompt without exiting
• If there is code running, Ctrl-C first interrupts the thread to try and force a gentle exit. A second Ctrl-C would then terminate the process.

Unfortunately we will no longer be able to terminate the thread forcefully, as Thread.stop is busted Java >20 (see com-lihaoyi/Ammonite#1379), so using Thread.interrupt and sys.exit is the best we have

Tested manually using bin/scala. Doesn't work in sbt repl due to SBT also intercepting the signal, but that's a separate issue we can follow up later

[bishabosha]

scala> while true do
     |   Thread.sleep(1000)
     |   println("still alive!")
     |
still alive!
still alive!
^C
Interrupting running thread, Ctrl-C again to terminate the REPL Process
java.lang.InterruptedException: sleep interrupted
  at java.base/java.lang.Thread.sleep(Native Method)
  ... 32 elided

scala>

Nice!

[bishabosha]

the double Ctl+c doesn't quit for me but keeps resetting the prompt

Edit: it has to be a true infinite loop, with no yielding, for double interrupt to work (so no sleep)

[lihaoyi]

Ctrl-C only exits the process when it is running code that it is unable to interrupt. Doesn't need to be infinite, as long as it's running: the first Ctrl-C will ask for confirmation, the second Ctrl-C will exit the process