scripts: do not get confused with HEAD in work tree

When you have a file called HEAD in your work tree, many commands that
our scripts feed "HEAD" to would complain about the rev vs path
ambiguity.  A solution is to form command line more carefully by
appending -- to them, which makes it clear that we mean HEAD rev not
HEAD file.

This patch would apply to maint.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-am.sh

@@ -214,7 +214,7 @@ fi
 
 case "$resolved" in
 '')
-	files=$(git diff-index --cached --name-only HEAD) || exit
+	files=$(git diff-index --cached --name-only HEAD --) || exit
 	if [ "$files" ]; then
 	   echo "Dirty index: cannot apply patches (dirty: $files)" >&2
 	   exit 1
@@ -348,7 +348,7 @@ do
 		case "$resolved$interactive" in
 		tt)
 			# This is used only for interactive view option.
-			git diff-index -p --cached HEAD >"$dotest/patch"
+			git diff-index -p --cached HEAD -- >"$dotest/patch"
 			;;
 		esac
 	esac
@@ -409,7 +409,7 @@ do
 		# trust what the user has in the index file and the
 		# working tree.
 		resolved=
-		git diff-index --quiet --cached HEAD && {
+		git diff-index --quiet --cached HEAD -- && {
 			echo "No changes - did you forget to use 'git add'?"
 			stop_here_user_resolve $this
 		}
@@ -431,7 +431,7 @@ do
 		then
 		    # Applying the patch to an earlier tree and merging the
 		    # result may have produced the same tree as ours.
-		    git diff-index --quiet --cached HEAD && {
+		    git diff-index --quiet --cached HEAD -- && {
 			echo No changes -- Patch already applied.
 			go_next
 			continue

git-filter-branch.sh

@@ -95,7 +95,7 @@ USAGE="[--env-filter <command>] [--tree-filter <command>] \
 . git-sh-setup
 
 git diff-files --quiet &&
-	git diff-index --cached --quiet HEAD ||
+	git diff-index --cached --quiet HEAD -- ||
 	die "Cannot rewrite branch(es) with a dirty working directory."
 
 tempdir=.git-rewrite

git-merge-ours.sh

@@ -9,6 +9,6 @@
 # because the current index is what we will be committing as the
 # merge result.
 
-git diff-index --quiet --cached HEAD || exit 2
+git diff-index --quiet --cached HEAD -- || exit 2
 
 exit 0

git-rebase--interactive.sh

@@ -52,7 +52,7 @@ require_clean_work_tree () {
 	git rev-parse --verify HEAD > /dev/null &&
 	git update-index --refresh &&
 	git diff-files --quiet &&
-	git diff-index --cached --quiet HEAD ||
+	git diff-index --cached --quiet HEAD -- ||
 	die "Working tree is dirty"
 }
 
@@ -331,7 +331,7 @@ do
 		git rev-parse --verify HEAD > /dev/null &&
 		git update-index --refresh &&
 		git diff-files --quiet &&
-		! git diff-index --cached --quiet HEAD &&
+		! git diff-index --cached --quiet HEAD -- &&
 		. "$DOTEST"/author-script &&
 		export GIT_AUTHOR_NAME GIT_AUTHOR_NAME GIT_AUTHOR_DATE &&
 		git commit -F "$DOTEST"/message -e

git-rebase.sh

@@ -60,7 +60,7 @@ continue_merge () {
 	fi
 
 	cmt=`cat "$dotest/current"`
-	if ! git diff-index --quiet HEAD
+	if ! git diff-index --quiet HEAD --
 	then
 		if ! git-commit -C "$cmt"
 		then
@@ -253,7 +253,7 @@ fi
 
 # The tree must be really really clean.
 git update-index --refresh || exit
-diff=$(git diff-index --cached --name-status -r HEAD)
+diff=$(git diff-index --cached --name-status -r HEAD --)
 case "$diff" in
 ?*)	echo "cannot rebase: your index is not up-to-date"
 	echo "$diff"

git-stash.sh

@@ -14,7 +14,7 @@ trap 'rm -f "$TMP-*"' 0
 ref_stash=refs/stash
 
 no_changes () {
-	git diff-index --quiet --cached HEAD &&
+	git diff-index --quiet --cached HEAD -- &&
 	git diff-files --quiet
 }