Add zsh completion

* Update help description and README.md

Signed-off-by: Silvin Lubecki <silvin.lubecki@docker.com>

README.md

@@ -250,7 +250,7 @@ Options:
   -v, --version            Print version information
 
 Commands:
-  completion  Generates bash completion scripts
+  completion  Generates completion scripts for the specified shell (bash or zsh)
   deploy      Deploy or update an application
   fork        Create a fork of an existing application to be modified
   helm        Generate a Helm chart
@@ -265,3 +265,28 @@ Commands:
 
 Run 'docker-app COMMAND --help' for more information on a command.
 ```
+
+## Shell completion
+
+### Bash
+
+Load the docker-app completion code for bash into the current shell:
+```sh
+$ source <(docker-app completion bash)
+```
+Set the docker-app completion code for bash to autoload on startup in your ~/.bashrc, ~/.profile or ~/.bash_profile:
+```sh
+source <(docker-app completion bash)
+```
+**Note**: `bash-completion` is needed.
+
+### Zsh
+
+Load the docker-app completion code for zsh into the current shell
+```sh
+$ source <(docker-app completion zsh)
+```
+Set the docker-app completion code for zsh to autoload on startup in your ~/.zshrc
+```sh
+source <(docker-app completion zsh)
+```

cmd/docker-app/completion.go

@@ -1,27 +1,187 @@
 package main
 
 import (
+	"bytes"
+	"fmt"
+	"io"
+
 	"github.com/docker/cli/cli"
 	"github.com/docker/cli/cli/command"
 	"github.com/spf13/cobra"
 )
 
 func completionCmd(dockerCli command.Cli, rootCmd *cobra.Command) *cobra.Command {
 	return &cobra.Command{
-		Use:   "completion",
-		Short: "Generates bash completion scripts",
-		Long: `To load completion run
-
-. <(docker-app completion)
+		Use:   "completion SHELL",
+		Short: "Generates completion scripts for the specified shell (bash or zsh)",
+		Long: `# Load the docker-app completion code for bash into the current shell
+. <(docker-app completion bash)
+# Set the docker-app completion code for bash to autoload on startup in your ~/.bashrc,
+# ~/.profile or ~/.bash_profile
+. <(docker-app completion bash)
+# Note: bash-completion is needed.
 
-To configure your bash shell to load completions for each session add to your bashrc
-
-# ~/.bashrc or ~/.profile
-. <(docker-app completion)
+# Load the docker-app completion code for zsh into the current shell
+source <(docker-app completion zsh)
+# Set the docker-app completion code for zsh to autoload on startup in your ~/.zshrc
+source <(docker-app completion zsh)
 `,
-		Args: cli.NoArgs,
+		Args: cli.RequiresMaxArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
-			return rootCmd.GenBashCompletion(dockerCli.Out())
+			switch {
+			case len(args) == 0:
+				return rootCmd.GenBashCompletion(dockerCli.Out())
+			case args[0] == "bash":
+				return rootCmd.GenBashCompletion(dockerCli.Out())
+			case args[0] == "zsh":
+				return runCompletionZsh(dockerCli.Out(), rootCmd)
+			default:
+				return fmt.Errorf("%q is not a supported shell", args[0])
+			}
 		},
 	}
 }
+
+const (
+	// Largely inspired by https://github.com/kubernetes/kubernetes/blob/master/pkg/kubectl/cmd/completion.go
+	zsh_head = `#compdef dockerapp
+__dockerapp_bash_source() {
+	alias shopt=':'
+	alias _expand=_bash_expand
+	alias _complete=_bash_comp
+	emulate -L sh
+	setopt kshglob noshglob braceexpand
+ 	source "$@"
+}
+ __dockerapp_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 [ "$1" = "__dockerapp_compopt" ]; then
+			echo builtin
+			return 0
+		fi
+	fi
+	type "$@"
+}
+ __dockerapp_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
+}
+ __dockerapp_compopt() {
+	true # don't do anything. Not supported by bashcompinit in zsh
+}
+ __dockerapp_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]#"$colon_word"}
+		done
+	fi
+}
+ __dockerapp_get_comp_words_by_ref() {
+	cur="${COMP_WORDS[COMP_CWORD]}"
+	prev="${COMP_WORDS[${COMP_CWORD}-1]}"
+	words=("${COMP_WORDS[@]}")
+	cword=("${COMP_CWORD[@]}")
+}
+ __dockerapp_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}\" = *.$1 || -d \"\${w}\" ]]"; then
+			qw="$(__dockerapp_quote "${w}")"
+			if [ -d "${w}" ]; then
+				COMPREPLY+=("${qw}/")
+			else
+				COMPREPLY+=("${qw}")
+			fi
+		fi
+	done
+}
+ __dockerapp_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
+ __dockerapp_convert_bash_to_zsh() {
+	sed \
+	-e 's/declare -F/whence -w/' \
+	-e 's/_get_comp_words_by_ref "\$@"/_get_comp_words_by_ref "\$*"/' \
+	-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}/__dockerapp_filedir/g" \
+	-e "s/${LWORD}_get_comp_words_by_ref${RWORD}/__dockerapp_get_comp_words_by_ref/g" \
+	-e "s/${LWORD}__ltrim_colon_completions${RWORD}/__dockerapp_ltrim_colon_completions/g" \
+	-e "s/${LWORD}compgen${RWORD}/__dockerapp_compgen/g" \
+	-e "s/${LWORD}compopt${RWORD}/__dockerapp_compopt/g" \
+	-e "s/${LWORD}declare${RWORD}/builtin declare/g" \
+	-e "s/\\\$(type${RWORD}/\$(__dockerapp_type/g" \
+	<<'BASH_COMPLETION_EOF'
+`
+	zsh_tail = `
+BASH_COMPLETION_EOF
+}
+ __dockerapp_bash_source <(__dockerapp_convert_bash_to_zsh)
+_complete dockerapp 2>/dev/null
+`
+)
+
+func runCompletionZsh(out io.Writer, rootCmd *cobra.Command) error {
+	fmt.Fprint(out, zsh_head)
+	buf := new(bytes.Buffer)
+	rootCmd.GenBashCompletion(buf)
+	fmt.Fprint(out, buf.String())
+	fmt.Fprint(out, zsh_tail)
+	return nil
+}