bash-completion: Support running when set -u is enabled

Under "set -u" semantics, it is an error to access undefined variables.
Some user environments may enable this setting in the interactive shell.

In any context where the completion functions access an undefined
variable, accessing a default empty string (aka "${1-}" instead of "$1")
is a reasonable way to code the function, as it silences the undefined
variable error while still supplying an empty string.

In this patch, functions that should always take an argument still use
$1. Functions that have optional arguments use ${1-}.

Signed-off-by: Ted Pavlic <ted@tedpavlic.com>
Acked-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -52,7 +52,7 @@ esac
 
 __gitdir ()
 {
-	if [ -z "$1" ]; then
+	if [ -z "${1-}" ]; then
 		if [ -n "$__git_dir" ]; then
 			echo "$__git_dir"
 		elif [ -d .git ]; then
@@ -111,7 +111,7 @@ __git_ps1 ()
 			fi
 		fi
 
-		if [ -n "$1" ]; then
+		if [ -n "${1-}" ]; then
 			printf "$1" "${b##refs/heads/}$r"
 		else
 			printf " (%s)" "${b##refs/heads/}$r"
@@ -143,22 +143,22 @@ __gitcomp ()
 		;;
 	*)
 		local IFS=$'\n'
-		COMPREPLY=($(compgen -P "$2" \
-			-W "$(__gitcomp_1 "$1" "$4")" \
+		COMPREPLY=($(compgen -P "${2-}" \
+			-W "$(__gitcomp_1 "${1-}" "${4-}")" \
 			-- "$cur"))
 		;;
 	esac
 }
 
 __git_heads ()
 {
-	local cmd i is_hash=y dir="$(__gitdir "$1")"
+	local cmd i is_hash=y dir="$(__gitdir "${1-}")"
 	if [ -d "$dir" ]; then
 		git --git-dir="$dir" for-each-ref --format='%(refname:short)' \
 			refs/heads
 		return
 	fi
-	for i in $(git ls-remote "$1" 2>/dev/null); do
+	for i in $(git ls-remote "${1-}" 2>/dev/null); do
 		case "$is_hash,$i" in
 		y,*) is_hash=n ;;
 		n,*^{}) is_hash=y ;;
@@ -170,13 +170,13 @@ __git_heads ()
 
 __git_tags ()
 {
-	local cmd i is_hash=y dir="$(__gitdir "$1")"
+	local cmd i is_hash=y dir="$(__gitdir "${1-}")"
 	if [ -d "$dir" ]; then
 		git --git-dir="$dir" for-each-ref --format='%(refname:short)' \
 			refs/tags
 		return
 	fi
-	for i in $(git ls-remote "$1" 2>/dev/null); do
+	for i in $(git ls-remote "${1-}" 2>/dev/null); do
 		case "$is_hash,$i" in
 		y,*) is_hash=n ;;
 		n,*^{}) is_hash=y ;;
@@ -188,7 +188,7 @@ __git_tags ()
 
 __git_refs ()
 {
-	local i is_hash=y dir="$(__gitdir "$1")"
+	local i is_hash=y dir="$(__gitdir "${1-}")"
 	local cur="${COMP_WORDS[COMP_CWORD]}" format refs
 	if [ -d "$dir" ]; then
 		case "$cur" in