git-checkout: disallow --detach on unborn branch

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 4c20dae34d2fc095195d91adae0af26087306277..a94b553d054b28eee83ce6b9bd54be4659279239 100644 (file)
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -916,6 +916,19 @@ static int parse_branchname_arg(int argc, const char **argv,
        return argcount;
 }
 
+static int switch_unborn_to_new_branch(struct checkout_opts *opts)
+{
+       int status;
+       struct strbuf branch_ref = STRBUF_INIT;
+
+       if (!opts->new_branch)
+               die(_("You are on a branch yet to be born"));
+       strbuf_addf(&branch_ref, "refs/heads/%s", opts->new_branch);
+       status = create_symref("HEAD", branch_ref.buf, "checkout -b");
+       strbuf_release(&branch_ref);
+       return status;
+}
+
 int cmd_checkout(int argc, const char **argv, const char *prefix)
 {
        struct checkout_opts opts;
@@ -1089,5 +1102,13 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
        if (opts.writeout_stage)
                die(_("--ours/--theirs is incompatible with switching branches."));
 
+       if (!new.commit) {
+               unsigned char rev[20];
+               int flag;
+
+               resolve_ref("HEAD", rev, 0, &flag);
+               if ((flag & REF_ISSYMREF) && is_null_sha1(rev))
+                       return switch_unborn_to_new_branch(&opts);
+       }
        return switch_branches(&opts, &new);
 }