[PATCH] prevent checkout from creating branches that start with a dash

[Bart Trojanowski <bart@jukie.net>]

It was previously possible to create a -f branch with git-checkout, which
could not be used or deleted.

        $ git checkout -b -f master
        Switched to a new branch "-f"

Signed-off-by: Bart Trojanowski <bart@jukie.net>
---
 branch.c           |   11 +++++++++++
 branch.h           |    5 +++++
 builtin-checkout.c |    4 ++++
 3 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/branch.c b/branch.c
index 56e9492..c25e362 100644
--- a/branch.c
+++ b/branch.c
@@ -170,3 +170,14 @@ void remove_branch_state(void)
 	unlink(git_path("MERGE_MSG"));
 	unlink(git_path("SQUASH_MSG"));
 }
+
+int validate_branch_name(const char *branch_name)
+{
+	if (!*branch_name)
+		return -1;
+
+	if (*branch_name == '-')
+		return -1;
+
+	return 0;
+}
diff --git a/branch.h b/branch.h
index 9f0c2a2..13999ba 100644
--- a/branch.h
+++ b/branch.h
@@ -21,4 +21,9 @@ void create_branch(const char *head, const char *name, const char *start_name,
  */
 void remove_branch_state(void);
 
+/*
+ * Check if the branch name given is well formed.  Returns 0 on success.
+ */
+int validate_branch_name(const char *branch_name);
+
 #endif
diff --git a/builtin-checkout.c b/builtin-checkout.c
index 93ea69b..f425646 100644
--- a/builtin-checkout.c
+++ b/builtin-checkout.c
@@ -553,6 +553,10 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	if (opts.force && opts.merge)
 		die("git checkout: -f and -m are incompatible");
 
+	if (opts.new_branch && validate_branch_name(opts.new_branch))
+		die("git checkout: '%s' does not look like a valid branch name",
+				opts.new_branch);
+
 	if (argc) {
 		const char **pathspec = get_pathspec(prefix, argv);
 
-- 
1.5.6.1.109.ga974cd.dirty