bash: use for-each-ref format 'refname:short'

Using this format simplifies the code for completing refs and (in some
cases) improves performance significantly.

For repositories like the current git.git (with more than 200 refs)
there is no real performance difference, but for a repository with 2000
refs the total time needed to complete the refs is reduced by ~25% (from
around 400ms to around 305ms).

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Acked-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -154,11 +154,8 @@ __git_heads ()
 {
 	local cmd i is_hash=y dir="$(__gitdir "$1")"
 	if [ -d "$dir" ]; then
-		for i in $(git --git-dir="$dir" \
-			for-each-ref --format='%(refname)' \
-			refs/heads ); do
-			echo "${i#refs/heads/}"
-		done
+		git --git-dir="$dir" for-each-ref --format='%(refname:short)' \
+			refs/heads
 		return
 	fi
 	for i in $(git ls-remote "$1" 2>/dev/null); do
@@ -175,11 +172,8 @@ __git_tags ()
 {
 	local cmd i is_hash=y dir="$(__gitdir "$1")"
 	if [ -d "$dir" ]; then
-		for i in $(git --git-dir="$dir" \
-			for-each-ref --format='%(refname)' \
-			refs/tags ); do
-			echo "${i#refs/tags/}"
-		done
+		git --git-dir="$dir" for-each-ref --format='%(refname:short)' \
+			refs/tags
 		return
 	fi
 	for i in $(git ls-remote "$1" 2>/dev/null); do
@@ -197,16 +191,8 @@ __git_refs ()
 	local cmd i is_hash=y dir="$(__gitdir "$1")"
 	if [ -d "$dir" ]; then
 		if [ -e "$dir/HEAD" ]; then echo HEAD; fi
-		for i in $(git --git-dir="$dir" \
-			for-each-ref --format='%(refname)' \
-			refs/tags refs/heads refs/remotes); do
-			case "$i" in
-				refs/tags/*)    echo "${i#refs/tags/}" ;;
-				refs/heads/*)   echo "${i#refs/heads/}" ;;
-				refs/remotes/*) echo "${i#refs/remotes/}" ;;
-				*)              echo "$i" ;;
-			esac
-		done
+		git --git-dir="$dir" for-each-ref --format='%(refname:short)' \
+			refs/tags refs/heads refs/remotes
 		return
 	fi
 	for i in $(git ls-remote "$dir" 2>/dev/null); do