Offer zsh-autosuggestion as a completion candidate

autosuggest-complete.zsh

# Make the autosuggestion a completion value
function _autosuggest_complete() {
	local -a candidates

	# IMPROVEMENT: If we can be sure that autosuggest has already run we can
	#              just grab the suggestion variable, avoiding the double call
	local orignal_ZSH_AUTOSUGGEST_USE_ASYNC=$ZSH_AUTOSUGGEST_USE_ASYNC
	ZSH_AUTOSUGGEST_USE_ASYNC=0 # need the result immediately
	_zsh_autosuggest_strategy_$ZSH_AUTOSUGGEST_STRATEGY "$BUFFER"
	ZSH_AUTOSUGGEST_USE_ASYNC=$orignal_ZSH_AUTOSUGGEST_USE_ASYNC

	# Escape ':' since it has special meaning to _describe
	candidates=( ${${suggestion[$((CURSOR-$#PREFIX+1)),-1]}//:\\:} )
	_describe -t auto-suggestion auto-suggestion candidates -Q
}
# Functions marked with '-first-' is called first by the '_complete' completer
compdef _autosuggest_complete -first-