bash-it/plugins/available/alias-completion.plugin.bash

# shellcheck shell=bash
# Load after the other completions to understand what needs to be completed
# BASH_IT_LOAD_PRIORITY: 365

cite about-plugin
about-plugin 'Automatic completion of aliases'

# References:
# http://superuser.com/a/437508/119764
# http://stackoverflow.com/a/1793178/1228454

# This needs to be a plugin so it gets executed after the completions and the aliases have been defined.
# Bash-it loads its components in the order
# 1) Aliases
# 2) Completions
# 3) Plugins
# 4) Custom scripts

# Automatically add completion for all aliases to commands having completion functions
function alias_completion {
	local namespace="alias_completion"
	local tmp_file completion_loader alias_name alias_tokens line completions
	local alias_arg_words new_completion compl_func compl_wrapper

	# parse function based completion definitions, where capture group 2 => function and 3 => trigger
	local compl_regex='complete( +[^ ]+)* -F ([^ ]+) ("[^"]+"|[^ ]+)'
	# parse alias definitions, where capture group 1 => trigger, 2 => command, 3 => command arguments
	local alias_regex="alias( -- | )([^=]+)='(\"[^\"]+\"|[^ ]+)(( +[^ ]+)*)'"

	# create array of function completion triggers, keeping multi-word triggers together
	eval "completions=($(complete -p | sed -Ene "/$compl_regex/s//'\3'/p"))"
	((${#completions[@]} == 0)) && return 0

	# create temporary file for wrapper functions and completions
	tmp_file="$(mktemp -t "${namespace}-${RANDOM}XXXXXX")" || return 1

	completion_loader="$(complete -p -D 2> /dev/null | sed -Ene 's/.* -F ([^ ]*).*/\1/p')"

	# read in "<alias> '<aliased command>' '<command args>'" lines from defined aliases
	# some aliases do have backslashes that needs to be interpreted
	# shellcheck disable=SC2162
	while read line; do
		eval "alias_tokens=($line)" 2> /dev/null || continue # some alias arg patterns cause an eval parse error
		# shellcheck disable=SC2154 # see `eval` above
		alias_name="${alias_tokens[0]}" alias_cmd="${alias_tokens[1]}" alias_args="${alias_tokens[2]# }"

		# skip aliases to pipes, boolean control structures and other command lists
		# (leveraging that eval errs out if $alias_args contains unquoted shell metacharacters)
		eval "alias_arg_words=($alias_args)" 2> /dev/null || continue
		# avoid expanding wildcards
		read -a alias_arg_words <<< "$alias_args"

		# skip alias if there is no completion function triggered by the aliased command
		if ! _bash-it-array-contains-element "$alias_cmd" "${completions[@]}"; then
			if [[ -n "$completion_loader" ]]; then
				# force loading of completions for the aliased command
				eval "$completion_loader $alias_cmd"
				# 124 means completion loader was successful
				[[ $? -eq 124 ]] || continue
				completions+=("$alias_cmd")
			else
				continue
			fi
		fi
		new_completion="$(complete -p "$alias_cmd" 2> /dev/null)"

		# create a wrapper inserting the alias arguments if any
		if [[ -n $alias_args ]]; then
			compl_func="${new_completion/#* -F /}"
			compl_func="${compl_func%% *}"
			# avoid recursive call loops by ignoring our own functions
			if [[ "${compl_func#_"$namespace"::}" == "$compl_func" ]]; then
				compl_wrapper="_${namespace}::${alias_name}"
				echo "function $compl_wrapper {
                        local compl_word=\$2
                        local prec_word=\$3
                        # check if prec_word is the alias itself. if so, replace it
                        # with the last word in the unaliased form, i.e.,
                        # alias_cmd + ' ' + alias_args.
                        if [[ \$COMP_LINE == \"\$prec_word \$compl_word\" ]]; then
                            prec_word='$alias_cmd $alias_args'
                            prec_word=\${prec_word#* }
                        fi
                        (( COMP_CWORD += ${#alias_arg_words[@]} ))
                        COMP_WORDS=($alias_cmd $alias_args \${COMP_WORDS[@]:1})
                        (( COMP_POINT -= \${#COMP_LINE} ))
                        COMP_LINE=\${COMP_LINE/$alias_name/$alias_cmd $alias_args}
                        (( COMP_POINT += \${#COMP_LINE} ))
                        $compl_func \"$alias_cmd\" \"\$compl_word\" \"\$prec_word\"
                    }" >> "$tmp_file"
				new_completion="${new_completion/ -F $compl_func / -F $compl_wrapper }"
			fi
		fi

		# replace completion trigger by alias
		if [[ -n $new_completion ]]; then
			new_completion="${new_completion% *} $alias_name"
			echo "$new_completion" >> "$tmp_file"
		fi
	done < <(alias -p | sed -Ene "s/$alias_regex/\2 '\3' '\4'/p")
	# shellcheck source=/dev/null
	source "$tmp_file" && command rm -f "$tmp_file"
}

alias_completion