Merge branch 'rs/checkout-b-track-error'

The error message from "git checkout -b foo -t bar baz" was
confusing.

* rs/checkout-b-track-error:
  checkout: improve error messages for -b with extra argument
  checkout: add tests for -b and --track

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);
 

t/t2018-checkout-branch.sh

@@ -260,4 +260,14 @@ test_expect_success 'checkout -b to a new branch preserves mergeable changes des
 	test_cmp expect actual
 '
 
+test_expect_success 'checkout -b rejects an invalid start point' '
+	test_must_fail git checkout -b branch4 file1 2>err &&
+	test_i18ngrep "is not a commit" err
+'
+
+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
+'
+
 test_done

t/t2027-checkout-track.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+
+test_description='tests for git branch --track'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit one &&
+	test_commit two
+'
+
+test_expect_success 'checkout --track -b creates a new tracking branch' '
+	git checkout --track -b branch1 master &&
+	test $(git rev-parse --abbrev-ref HEAD) = branch1 &&
+	test $(git config --get branch.branch1.remote) = . &&
+	test $(git config --get branch.branch1.merge) = refs/heads/master
+'
+
+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
+'
+
+test_done