Cancel completion, but only completion, in zsh

Question

When a completion function takes a long time, I can interrupt it by pressing Ctrl+C (terminal interrupt key, sends SIGINT) or Ctrl+G (bound to send-break). I am then left with the uncompleted word.

However, if I happen to hit Ctrl+C or Ctrl+G just as the completion function finishes, my key press may cancel the command line and give me a fresh prompt instead of cancelling the completion.

How can I set up zsh so that a certain key will cancel an ongoing completion but do nothing if no completion function is active?

Answer 1

Here's a solution that sets up a SIGINT handler that makes Ctrl+C only interrupt when completion is active.

# A completer widget that sets a flag for the duration of
# the completion so the SIGINT handler knows whether completion
# is active. It would be better if we could check some internal
# zsh parameter to determine if completion is running, but as 
# far as I'm aware that isn't possible.
function interruptible-expand-or-complete {
 COMPLETION_ACTIVE=1
 # Bonus feature: automatically interrupt completion
 # after a three second timeout.
 # ( sleep 3; kill -INT $$ ) &!
 zle expand-or-complete
 COMPLETION_ACTIVE=0
}
# Bind our completer widget to tab.
zle -N interruptible-expand-or-complete
bindkey '^I' interruptible-expand-or-complete
# Interrupt only if completion is active.
function TRAPINT {
 if [[ $COMPLETION_ACTIVE == 1 ]]; then
 COMPLETION_ACTIVE=0
 zle -M "Completion canceled." 
 # Returning non-zero tells zsh to handle SIGINT,
 # which will interrupt the completion function. 
 return 1
 else
 # Returning zero tells zsh that we handled SIGINT;
 # don't interrupt whatever is currently running.
 return 0
 fi
}

Answer 2

I don't know if this is an acceptable solution or not, but sending a SIGSTOP (Ctrl+S) seems to have the desired effect, with the added benefit that you can start up the autocomplete again if you send a SIGSTART (Ctrl+Q) before typing anything else. I'm not an expert on job control though, so this may leave some additional clutter related to the stopped job.

• Gilles 'SO- stop being evil': Ctrl+S and Ctrl+Q are flow control commands. They only affect output to the terminal, which is irrelevant here. Predictably, Ctrl+S has no effect during completion (zsh disables the terminal setting anyway, it grabs the key combination). Pressing Ctrl+Z (which sends SIGTOP) has no effect either.
• Aaron Okano: Thanks! I wasn't entirely sure what was going on in the background. All I saw was that I got control of the terminal back.