Description

Many commands can generate zsh completions, which is very useful. Unfortunately, running many such commands slows down zsh startup. (A notable example is pipenv, which takes over a second.)

I have seen a number of zsh plugins/modules use a trick where they only generate the completion function if it does not exist, or the command binary is newer. I have generalized this mechanism in my own zsh customization module:

local gendir="${0:h}/generated-functions"
fpath=("$gendir" $fpath)

# Generate a completion function
# usage: gencomp COMMAND ARGS...
# example: gencomp kubectl completion zsh
function gencomp() {
  gencompx '' "$@"
}

# Generate a completion function and add an extra line at the bottom of the file
# usage: gencompx LINE COMMAND ARGS...
# example: gencompx __start_helm helm completion zsh
function gencompx() {
  local tail="$1"
  shift
  (( $+commands[$1] )) || return
  local genfile="$gendir/_$1"
  if [[ ! $commands[$1] -ot "$genfile" ]]; then
    "$@" >! "$genfile"
    [[ "$tail" ]] && echo "$tail" >> "$genfile"
  fi
}

The gencompx function is used when the completion does not add a call to the function itself, otherwise you need to press tab twice the first time. The contents of the generated-functions directory is not committed to version control, obviously.

Question: does in make sense to include this mechanism in prezto itself? I'd be happy to provide a pull request.

Apart from that, any corrections or suggestions are also very welcome. I have not dived into zsh/prezto too deeply, so I might have missed an existing similar feature.