complete: zsh: use zsh completion for the main cmd

So that we can have a nice zsh completion output:

% git <tab>
add       -- add file contents to the index
bisect    -- find by binary search the change that introduced a bug
branch    -- list, create, or delete branches
checkout  -- checkout a branch or paths to the working tree
clone     -- clone a repository into a new directory
commit    -- record changes to the repository
diff      -- show changes between commits, commit and working tree, etc
fetch     -- download objects and refs from another repository
grep      -- print lines matching a pattern
init      -- create an empty Git repository or reinitialize an existing one
log       -- show commit logs
merge     -- join two or more development histories together
mv        -- move or rename a file, a directory, or a symlink
pull      -- fetch from and merge with another repository or a local branch
push      -- update remote refs along with associated objects
rebase    -- forward-port local commits to the updated upstream head
reset     -- reset current HEAD to the specified state
rm        -- remove files from the working tree and from the index
show      -- show various types of objects
status    -- show the working tree status
tag       -- create, list, delete or verify a tag object signed with GPG

And other niceties, like 'git --git-dir=<tab>' showing only directories.

For the rest, the bash completion stuff is still used.

Also, add my copyright, since this more than a thin wrapper.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Felipe Contreras

contrib/completion/git-completion.zsh

@@ -2,6 +2,8 @@
 
 # zsh completion wrapper for git
 #
+# Copyright (c) 2012-2013 Felipe Contreras <felipe.contreras@gmail.com>
+#
 # You need git's bash completion script installed somewhere, by default on the
 # same directory as this script.
 #
@@ -21,6 +23,9 @@ complete ()
 	return 0
 }
 
+zstyle -T ':completion:*:*:git:*' tag-order && \
+	zstyle ':completion:*:*:git:*' tag-order 'common-commands'
+
 zstyle -s ":completion:*:*:git:*" script script
 test -z "$script" && script="$(dirname ${funcsourcetrace[1]%:*})"/git-completion.bash
 ZSH_VERSION='' . "$script"
@@ -69,6 +74,115 @@ __gitcomp_file ()
 	compadd -Q -p "${2-}" -f -- ${=1} && _ret=0
 }
 
+__git_zsh_bash_func ()
+{
+	emulate -L ksh
+
+	local command=$1
+
+	local completion_func="_git_${command//-/_}"
+	declare -f $completion_func >/dev/null && $completion_func && return
+
+	local expansion=$(__git_aliased_command "$command")
+	if [ -n "$expansion" ]; then
+		completion_func="_git_${expansion//-/_}"
+		declare -f $completion_func >/dev/null && $completion_func
+	fi
+}
+
+__git_zsh_cmd_common ()
+{
+	local -a list
+	list=(
+	add:'add file contents to the index'
+	bisect:'find by binary search the change that introduced a bug'
+	branch:'list, create, or delete branches'
+	checkout:'checkout a branch or paths to the working tree'
+	clone:'clone a repository into a new directory'
+	commit:'record changes to the repository'
+	diff:'show changes between commits, commit and working tree, etc'
+	fetch:'download objects and refs from another repository'
+	grep:'print lines matching a pattern'
+	init:'create an empty Git repository or reinitialize an existing one'
+	log:'show commit logs'
+	merge:'join two or more development histories together'
+	mv:'move or rename a file, a directory, or a symlink'
+	pull:'fetch from and merge with another repository or a local branch'
+	push:'update remote refs along with associated objects'
+	rebase:'forward-port local commits to the updated upstream head'
+	reset:'reset current HEAD to the specified state'
+	rm:'remove files from the working tree and from the index'
+	show:'show various types of objects'
+	status:'show the working tree status'
+	tag:'create, list, delete or verify a tag object signed with GPG')
+	_describe -t common-commands 'common commands' list && _ret=0
+}
+
+__git_zsh_cmd_alias ()
+{
+	local -a list
+	list=(${${${(0)"$(git config -z --get-regexp '^alias\.')"}#alias.}%$'\n'*})
+	_describe -t alias-commands 'aliases' list $* && _ret=0
+}
+
+__git_zsh_cmd_all ()
+{
+	local -a list
+	emulate ksh -c __git_compute_all_commands
+	list=( ${=__git_all_commands} )
+	_describe -t all-commands 'all commands' list && _ret=0
+}
+
+__git_zsh_main ()
+{
+	local curcontext="$curcontext" state state_descr line
+	typeset -A opt_args
+	local -a orig_words
+
+	orig_words=( ${words[@]} )
+
+	_arguments -C \
+		'(-p --paginate --no-pager)'{-p,--paginate}'[pipe all output into ''less'']' \
+		'(-p --paginate)--no-pager[do not pipe git output into a pager]' \
+		'--git-dir=-[set the path to the repository]: :_directories' \
+		'--bare[treat the repository as a bare repository]' \
+		'(- :)--version[prints the git suite version]' \
+		'--exec-path=-[path to where your core git programs are installed]:: :_directories' \
+		'--html-path[print the path where git''s HTML documentation is installed]' \
+		'--info-path[print the path where the Info files are installed]' \
+		'--man-path[print the manpath (see `man(1)`) for the man pages]' \
+		'--work-tree=-[set the path to the working tree]: :_directories' \
+		'--namespace=-[set the git namespace]' \
+		'--no-replace-objects[do not use replacement refs to replace git objects]' \
+		'(- :)--help[prints the synopsis and a list of the most commonly used commands]: :->arg' \
+		'(-): :->command' \
+		'(-)*:: :->arg' && return
+
+	case $state in
+	(command)
+		_alternative \
+                         'alias-commands:alias:__git_zsh_cmd_alias' \
+                         'common-commands:common:__git_zsh_cmd_common' \
+                         'all-commands:all:__git_zsh_cmd_all' && _ret=0
+		;;
+	(arg)
+		local command="${words[1]}" __git_dir
+
+		if (( $+opt_args[--bare] )); then
+			__git_dir='.'
+		else
+			__git_dir=${opt_args[--git-dir]}
+		fi
+
+		(( $+opt_args[--help] )) && command='help'
+
+		words=( ${orig_words[@]} )
+
+		__git_zsh_bash_func $command
+		;;
+	esac
+}
+
 _git ()
 {
 	local _ret=1
@@ -78,7 +192,11 @@ _git ()
 	prev=${words[CURRENT-1]}
 	let cword=CURRENT-1
 
-	emulate ksh -c __${service}_main
+	if (( $+functions[__${service}_zsh_main] )); then
+		__${service}_zsh_main
+	else
+		emulate ksh -c __${service}_main
+	fi
 
 	let _ret && _default -S '' && _ret=0
 	return _ret