git-branch -d <branch>: delete unused branch.

The new flag '-d' lets you delete a branch.  For safety, it does not
lets you delete the branch you are currently on, nor a branch that
has been fully merged into your current branch.

The credit for the safety check idea goes to Daniel Barkalow.

Signed-off-by: Junio C Hamano <junkio@cox.net>

git-branch.sh

@@ -3,7 +3,7 @@
 . git-sh-setup || die "Not a git archive"
 
 usage () {
-    echo >&2 "usage: $(basename $0)"' [<branchname> [start-point]]
+    echo >&2 "usage: $(basename $0)"' [-d <branch>] | [<branch> [start-point]]
 
 If no arguments, show available branches and mark current branch with a star.
 If one argument, create a new branch <branchname> based off of current HEAD.
@@ -12,6 +12,59 @@ If two arguments, create a new branch <branchname> based off of <start-point>.
     exit 1
 }
 
+delete_branch () {
+    option="$1" branch_name="$2"
+    headref=$(readlink "$GIT_DIR/HEAD" | sed -e 's|^refs/heads/||')
+    case ",$headref," in
+    ",$branch_name,")
+	die "Cannot delete the branch you are on." ;;
+    ,,)
+	die "What branch are you on anyway?" ;;
+    esac
+    branch=$(cat "$GIT_DIR/refs/heads/$branch_name") &&
+	branch=$(git-rev-parse --verify "$branch^0") ||
+	    die "Seriously, what branch are you talking about?"
+    case "$option" in
+    -D)
+	;;
+    *)
+	mbs=$(git-merge-base -a "$branch" HEAD | tr '\012' ' ')
+	case " $mbs " in
+	*' '$branch' '*)
+	    # the merge base of branch and HEAD contains branch --
+	    # which means that the HEAD contains everything in the HEAD.
+	    ;;
+	*)
+	    echo >&2 "The branch '$branch_name' is not a strict subset of your current HEAD.
+If you are sure you want to delete it, run 'git branch -D $branch_name'."
+	    exit 1
+	    ;;
+	esac
+	;;
+    esac
+    rm -f "$GIT_DIR/refs/heads/$branch_name"
+    echo "Deleted branch $branch_name."
+    exit 0
+}
+
+while case "$#,$1" in 0,*) break ;; *,-*) ;; *) break ;; esac
+do
+	case "$1" in
+	-d | -D)
+		delete_branch "$1" "$2"
+		exit
+		;;
+	--)
+		shift
+		break
+		;;
+	-*)
+		usage
+		;;
+	esac
+	shift
+done
+
 case "$#" in
 0)
 	headref=$(readlink "$GIT_DIR/HEAD" | sed -e 's|^refs/heads/||')
@@ -36,11 +89,6 @@ case "$#" in
 esac
 branchname="$1"
 
-case "$branchname" in
--*)
-	usage;;
-esac
-
 rev=$(git-rev-parse --verify "$head") || exit
 
 [ -e "$GIT_DIR/refs/heads/$branchname" ] && die "$branchname already exists"