[PATCH 2/2] checkout: improve error messages for -b with extra argument

["René Scharfe" <l.s.r@web.de>]

When we try to create a branch "foo" based on "origin/master" and give
git commit -b an extra unsupported argument "bar", it confusingly
reports:

   $ git checkout -b foo origin/master bar
   fatal: 'bar' is not a commit and a branch 'foo' cannot be created from it

   $ git checkout --track -b foo origin/master bar
   fatal: 'bar' is not a commit and a branch 'foo' cannot be created from it

That's wrong, because it very well understands that "origin/master" is
supposed to be the start point for the new branch and not "bar".  Check
if we got a commit and show more fitting messages in that case instead:

   $ git checkout -b foo origin/master bar
   fatal: Cannot update paths and switch to branch 'foo' at the same time.

   $ git checkout --track -b foo origin/master bar
   fatal: '--track' cannot be used with updating paths

Original-patch-by: Jeff King <peff@peff.net>
Signed-off-by: René Scharfe <l.s.r@web.de>
---
 builtin/checkout.c         | 2 +-
 t/t2018-checkout-branch.sh | 2 +-
 t/t2027-checkout-track.sh  | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index e9d111bb83..24336e1017 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1689,7 +1689,7 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 		 * Try to give more helpful suggestion.
 		 * new_branch && argc > 1 will be caught later.
 		 */
-		if (opts->new_branch && argc == 1)
+		if (opts->new_branch && argc == 1 && !new_branch_info.commit)
 			die(_("'%s' is not a commit and a branch '%s' cannot be created from it"),
 				argv[0], opts->new_branch);

diff --git a/t/t2018-checkout-branch.sh b/t/t2018-checkout-branch.sh
index d99b699396..5b8c042997 100755
--- a/t/t2018-checkout-branch.sh
+++ b/t/t2018-checkout-branch.sh
@@ -265,7 +265,7 @@ test_expect_success 'checkout -b rejects an invalid start point' '
 	test_i18ngrep "is not a commit" err
 '

-test_expect_failure 'checkout -b rejects an extra path argument' '
+test_expect_success 'checkout -b rejects an extra path argument' '
 	test_must_fail git checkout -b branch4 branch1 file1 2>err &&
 	test_i18ngrep "Cannot update paths and switch to branch" err
 '
diff --git a/t/t2027-checkout-track.sh b/t/t2027-checkout-track.sh
index d0b41d7cd0..bcba1bf90c 100755
--- a/t/t2027-checkout-track.sh
+++ b/t/t2027-checkout-track.sh
@@ -16,7 +16,7 @@ test_expect_success 'checkout --track -b creates a new tracking branch' '
 	test $(git config --get branch.branch1.merge) = refs/heads/master
 '

-test_expect_failure 'checkout --track -b rejects an extra path argument' '
+test_expect_success 'checkout --track -b rejects an extra path argument' '
 	test_must_fail git checkout --track -b branch2 master one.t 2>err &&
 	test_i18ngrep "cannot be used with updating paths" err
 '
--
2.26.2