Add bash auto completion support

Adds auto completion support that's generated via:
```
$ kompose complete
```

This file is added to /etc/bash_completion.d/kompose.sh

README.md

@@ -70,12 +70,20 @@ Kompose is in Fedora 24 and 25 repositories. You can install it just like any ot
 sudo dnf -y install kompose
 ```
 
-## Bash Completion
+## Shell autocompletion
 
-Running this below command in order to benefit from bash completion
+We support both `bash` and `zsh` for autocompletion.
+
+Bash:
 
 ```console
-$ PROG=kompose source script/bash_autocomplete
+source <(kompose completion bash)
+```
+
+Zsh:
+
+```console
+source <(kompose completion zsh)
 ```
 
 ## Building

cmd/completion.go

@@ -0,0 +1,222 @@
+package cmd
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/Sirupsen/logrus"
+	"github.com/spf13/cobra"
+	"io"
+	"os"
+)
+
+var completion = &cobra.Command{
+	Use:   "completion SHELL",
+	Short: "Generate a bash auto completion file",
+	Long: `Generate a bash auto completion script.
+
+	Auto completion supports both bash and zsh.
+
+	The output is to stdout.
+
+	Examples:
+	$ source <(kompose completion bash)
+	$ source <(kompose completion zsh)
+
+	Will load the bash completion code.
+	`,
+
+	RunE: func(cmd *cobra.Command, args []string) error {
+
+		err := Generate(cmd, args)
+		if err != nil {
+			logrus.Fatalf("Error: %s", err)
+		}
+
+		return nil
+	},
+}
+
+// Generate the the approriate autocompletion file
+func Generate(cmd *cobra.Command, args []string) error {
+
+	// Check the passed in arguments
+	if len(args) == 0 {
+		return fmt.Errorf("Shell not specified. ex. kompose completion [bash|zsh]")
+	}
+	if len(args) > 1 {
+		return fmt.Errorf("Too many arguments. Expected only the shell type. ex. kompose completion [bash|zsh]")
+	}
+	shell := args[0]
+	if shell != "bash" && shell != "zsh" {
+	}
+
+	// Generate bash through cobra if selected
+	if shell == "bash" {
+		return cmd.Root().GenBashCompletion(os.Stdout)
+
+		// Generate zsh with the appropriate conversion as well as bash inclusion
+	} else if shell == "zsh" {
+		return runCompletionZsh(os.Stdout, cmd.Root())
+
+		// Else, return an error.
+	} else {
+		return fmt.Errorf("not a compatible shell, bash and zsh are only supported")
+	}
+}
+
+func init() {
+	RootCmd.AddCommand(completion)
+}
+
+/*
+	This is copied from
+	https://github.com/kubernetes/kubernetes/blob/ea18d5c32ee7c320fe96dda6b0c757476908e696/pkg/kubectl/cmd/completion.go
+	in order to generate ZSH completion support.
+*/
+func runCompletionZsh(out io.Writer, kompose *cobra.Command) error {
+
+	zshInitialization := `
+__kompose_bash_source() {
+	alias shopt=':'
+	alias _expand=_bash_expand
+	alias _complete=_bash_comp
+	emulate -L sh
+	setopt kshglob noshglob braceexpand
+	source "$@"
+}
+__kompose_type() {
+	# -t is not supported by zsh
+	if [ "$1" == "-t" ]; then
+		shift
+		# fake Bash 4 to disable "complete -o nospace". Instead
+		# "compopt +-o nospace" is used in the code to toggle trailing
+		# spaces. We don't support that, but leave trailing spaces on
+		# all the time
+		if [ "$1" = "__kompose_compopt" ]; then
+			echo builtin
+			return 0
+		fi
+	fi
+	type "$@"
+}
+__kompose_compgen() {
+	local completions w
+	completions=( $(compgen "$@") ) || return $?
+	# filter by given word as prefix
+	while [[ "$1" = -* && "$1" != -- ]]; do
+		shift
+		shift
+	done
+	if [[ "$1" == -- ]]; then
+		shift
+	fi
+	for w in "${completions[@]}"; do
+		if [[ "${w}" = "$1"* ]]; then
+			echo "${w}"
+		fi
+	done
+}
+__kompose_compopt() {
+	true # don't do anything. Not supported by bashcompinit in zsh
+}
+__kompose_declare() {
+	if [ "$1" == "-F" ]; then
+		whence -w "$@"
+	else
+		builtin declare "$@"
+	fi
+}
+__kompose_ltrim_colon_completions()
+{
+	if [[ "$1" == *:* && "$COMP_WORDBREAKS" == *:* ]]; then
+		# Remove colon-word prefix from COMPREPLY items
+		local colon_word=${1%${1##*:}}
+		local i=${#COMPREPLY[*]}
+		while [[ $((--i)) -ge 0 ]]; do
+			COMPREPLY[$i]=${COMPREPLY[$i]#"$colon_word"}
+		done
+	fi
+}
+__kompose_get_comp_words_by_ref() {
+	cur="${COMP_WORDS[COMP_CWORD]}"
+	prev="${COMP_WORDS[${COMP_CWORD}-1]}"
+	words=("${COMP_WORDS[@]}")
+	cword=("${COMP_CWORD[@]}")
+}
+__kompose_filedir() {
+	local RET OLD_IFS w qw
+	__debug "_filedir $@ cur=$cur"
+	if [[ "$1" = \~* ]]; then
+		# somehow does not work. Maybe, zsh does not call this at all
+		eval echo "$1"
+		return 0
+	fi
+	OLD_IFS="$IFS"
+	IFS=$'\n'
+	if [ "$1" = "-d" ]; then
+		shift
+		RET=( $(compgen -d) )
+	else
+		RET=( $(compgen -f) )
+	fi
+	IFS="$OLD_IFS"
+	IFS="," __debug "RET=${RET[@]} len=${#RET[@]}"
+	for w in ${RET[@]}; do
+		if [[ ! "${w}" = "${cur}"* ]]; then
+			continue
+		fi
+		if eval "[[ \"\${w}\" = *.$1 || -d \"\${w}\" ]]"; then
+			qw="$(__kompose_quote "${w}")"
+			if [ -d "${w}" ]; then
+				COMPREPLY+=("${qw}/")
+			else
+				COMPREPLY+=("${qw}")
+			fi
+		fi
+	done
+}
+__kompose_quote() {
+    if [[ $1 == \'* || $1 == \"* ]]; then
+        # Leave out first character
+        printf %q "${1:1}"
+    else
+    	printf %q "$1"
+    fi
+}
+autoload -U +X bashcompinit && bashcompinit
+# use word boundary patterns for BSD or GNU sed
+LWORD='[[:<:]]'
+RWORD='[[:>:]]'
+if sed --help 2>&1 | grep -q GNU; then
+	LWORD='\<'
+	RWORD='\>'
+fi
+__kompose_convert_bash_to_zsh() {
+	sed \
+	-e 's/declare -F/whence -w/' \
+	-e 's/local \([a-zA-Z0-9_]*\)=/local \1; \1=/' \
+	-e 's/flags+=("\(--.*\)=")/flags+=("\1"); two_word_flags+=("\1")/' \
+	-e 's/must_have_one_flag+=("\(--.*\)=")/must_have_one_flag+=("\1")/' \
+	-e "s/${LWORD}_filedir${RWORD}/__kompose_filedir/g" \
+	-e "s/${LWORD}_get_comp_words_by_ref${RWORD}/__kompose_get_comp_words_by_ref/g" \
+	-e "s/${LWORD}__ltrim_colon_completions${RWORD}/__kompose_ltrim_colon_completions/g" \
+	-e "s/${LWORD}compgen${RWORD}/__kompose_compgen/g" \
+	-e "s/${LWORD}compopt${RWORD}/__kompose_compopt/g" \
+	-e "s/${LWORD}declare${RWORD}/__kompose_declare/g" \
+	-e "s/\\\$(type${RWORD}/\$(__kompose_type/g" \
+	<<'BASH_COMPLETION_EOF'
+`
+	out.Write([]byte(zshInitialization))
+
+	buf := new(bytes.Buffer)
+	kompose.GenBashCompletion(buf)
+	out.Write(buf.Bytes())
+
+	zshTail := `
+BASH_COMPLETION_EOF
+}
+__kompose_bash_source <(__kompose_convert_bash_to_zsh)
+`
+	out.Write([]byte(zshTail))
+	return nil
+}