git checkout -b: allow switching out of an unborn branch

diff --git a/builtin/checkout.c b/builtin/checkout.c
index a5717f1637d9a018ba5f953bc356e84341b612cd..b76e2c0451cbeb73e1fd227c343413b1c8a33cc7 100644 (file)
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -715,10 +715,12 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
        unsigned char rev[20];
        int flag;
        memset(&old, 0, sizeof(old));
-       old.path = resolve_ref("HEAD", rev, 0, &flag);
+       old.path = xstrdup(resolve_ref("HEAD", rev, 0, &flag));
        old.commit = lookup_commit_reference_gently(rev, 1);
-       if (!(flag & REF_ISSYMREF))
+       if (!(flag & REF_ISSYMREF)) {
+               free((char *)old.path);
                old.path = NULL;
+       }
 
        if (old.path && !prefixcmp(old.path, "refs/heads/"))
                old.name = old.path + strlen("refs/heads/");
@@ -741,6 +743,7 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
        update_refs_for_switch(opts, &old, new);
 
        ret = post_checkout_hook(old.commit, new->commit, 1);
+       free((char *)old.path);
        return ret || opts->writeout_error;
 }
 
@@ -913,6 +916,17 @@ 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;
+
+       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;
@@ -1071,7 +1085,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
                if (strbuf_check_branch_ref(&buf, opts.new_branch))
                        die(_("git checkout: we do not like '%s' as a branch name."),
                            opts.new_branch);
-               if (!get_sha1(buf.buf, rev)) {
+               if (ref_exists(buf.buf)) {
                        opts.branch_exists = 1;
                        if (!opts.new_branch_force)
                                die(_("git checkout: branch %s already exists"),
@@ -1086,5 +1100,13 @@ 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);
 }