Re: Bug: "git checkout -b" should be allowed in empty repo

[Junio C Hamano <gitster@pobox.com>]

Junio C Hamano <gitster@pobox.com> writes:

> Note that I am not saying that we shouldn't add support for special cases
> with special case codepaths.
>
> Perhaps we would need to sprinkle more special case magic like this (this
> is for the special case that arises from the same cause)?
> ...

And the special case for "checkout -b" may look like this.

The early part of switch_branches() that computes old is probably be
better moved to the caller cmd_checkout() and used in the new code that
detects the "unborn" case, and passed as to switch_branches() as the third
parameter.  Such improvements, adding tests and pleasant commit log
message is left as an exercise for the interested and motivated, as usual
;-)



 builtin/checkout.c |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index f1984d9..195c40b 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -922,6 +922,19 @@ static int parse_branchname_arg(int argc, const char **argv,
 	return argcount;
 }
 
+static int switch_unborn_to_new_branch(struct checkout_opts *opts, const char *old_ref)
+{
+	int status;
+	struct strbuf branch_ref = STRBUF_INIT;
+
+	strbuf_addf(&branch_ref, "refs/heads/%s", opts->new_branch);
+	warning(_("Leaving the unborn branch '%s' behind..."),
+		skip_prefix(old_ref, "refs/heads/"));
+	status = create_symref("HEAD", branch_ref.buf, "checkout -b");
+	strbuf_reset(&branch_ref);
+	return status;
+}
+
 int cmd_checkout(int argc, const char **argv, const char *prefix)
 {
 	struct checkout_opts opts;
@@ -1093,5 +1106,16 @@ 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, status;
+		char *old_ref = resolve_refdup("HEAD", rev, 0, &flag);
+
+		if ((flag & REF_ISSYMREF) && is_null_sha1(rev)) {
+			status = switch_unborn_to_new_branch(&opts, old_ref);
+			free(old_ref);
+			return status;
+		}
+	}
 	return switch_branches(&opts, &new);
 }