Merge branch 'ab/checkout-branch-info-leakfix'

We added an unrelated sanity checking that leads to a BUG() while
plugging a leak, which triggered in a repository with symrefs in
the local branch namespace that point at a ref outside.  Partially
revert the change to avoid triggering the BUG().

* ab/checkout-branch-info-leakfix:
  checkout: avoid BUG() when hitting a broken repository

Author: gitster

builtin/checkout.c

@@ -1094,9 +1094,6 @@ static int switch_branches(const struct checkout_opts *opts,
 		const char *p;
 		if (skip_prefix(old_branch_info.path, prefix, &p))
 			old_branch_info.name = xstrdup(p);
-		else
-			BUG("should be able to skip past '%s' in '%s'!",
-			    prefix, old_branch_info.path);
 	}
 
 	if (opts->new_orphan_branch && opts->orphan_from_empty_tree) {

t/t2018-checkout-branch.sh

@@ -85,6 +85,19 @@ test_expect_success 'setup' '
 	git branch -m branch1
 '
 
+test_expect_success 'checkout a branch without refs/heads/* prefix' '
+	git clone --no-tags . repo-odd-prefix &&
+	(
+		cd repo-odd-prefix &&
+
+		origin=$(git symbolic-ref refs/remotes/origin/HEAD) &&
+		git symbolic-ref refs/heads/a-branch "$origin" &&
+
+		git checkout -f a-branch &&
+		git checkout -f a-branch
+	)
+'
+
 test_expect_success 'checkout -b to a new branch, set to HEAD' '
 	test_when_finished "
 		git checkout branch1 &&