checkout: improve error messages for -b with extra argument

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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/t/t2018-checkout-branch.sh b/t/t2018-checkout-branch.sh
index b166cb302f..5f761bc616 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 branch5 branch1 file1 2>err &&
 	test_i18ngrep "Cannot update paths and switch to branch" err
 '