Re: [PATCH] checkout: do not corrupt HEAD on empty repo

> In abe1998 ("git checkout -b: allow switching out of an unborn
> branch"), a code-path overly-optimisticly assumed that a
> branch-name was specified. This is not always the case, and as
> a result a NULL-pointer was attempted printed to .git/HEAD.
>
> This could lead to at least two different failure modes:
>  1) The CRT formated the NULL-string as something useful (e.g
>    "(null)")
>  2) The CRT crasheed.
>
> Neither were very convenient for formatting a new HEAD-reference.
>
> To fix this, reintroduce some strictness so we only take this
> new codepath if a banch-name was specified.
>
> Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
> ---
>  builtin/checkout.c         |    2 +-
>  t/t2015-checkout-unborn.sh |   11 +++++++++++
>  2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/builtin/checkout.c b/builtin/checkout.c
> index 23fc56d..35924d4 100644
> --- a/builtin/checkout.c
> +++ b/builtin/checkout.c
> @@ -1091,7 +1091,7 @@ 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) {
> +       if (!new.commit && opts.new_branch) {
>                unsigned char rev[20];
>                int flag;
>
> diff --git a/t/t2015-checkout-unborn.sh b/t/t2015-checkout-unborn.sh
> index 6352b74..2fa9458 100755
> --- a/t/t2015-checkout-unborn.sh
> +++ b/t/t2015-checkout-unborn.sh
> @@ -46,4 +46,15 @@ test_expect_success 'checking out another branch from unborn state' '
>        test_cmp expect actual
>  '
>
> +test_expect_success 'checking out in a newly created repo' '
> +       test_create_repo empty &&
> +       (
> +               cd empty &&
> +               cat .git/HEAD >expect &&
> +               test_must_fail git checkout &&
> +               cat .git/HEAD >actual &&
> +               test_cmp expect actual
> +       )
> +'
> +
>  test_done