lib/checkout: Fix regression in subpath for regular files

This is what caused the merge of
https://github.com/projectatomic/rpm-ostree/pull/652
to blow up, since https://github.com/ostreedev/ostree/pull/848
landed right before we tried to merge it.

When I was writing that PR I remember having an uncertain feeling
since we were doing a `mkdirat` above, but at the time I thought
we'd have test suite coverage...turns out we didn't.

For backwards compatibility, we need to continue to do a `mkdirat` here of the
parent. However...I can't think of a reason anyone would *want* that behavior.
Hence, let's add a special trick - if the destination name is `.`, we skip
`mkdirat()`. That way rpm-ostree for example can open a dfd for `/etc` and avoid
the `mkdir`.

Fold the subpath tests into `test-basic.sh` since it's not worth a separate
file. Add a test case for checking out a file.

Closes: #854
Approved by: jlebon

tests/basic-test.sh

@@ -341,6 +341,18 @@ cd ${test_tmpdir}
 $OSTREE checkout --subpath /yet/another test2 checkout-test2-subpath
 cd checkout-test2-subpath
 assert_file_has_content tree/green "leaf"
+cd ${test_tmpdir}
+rm checkout-test2-subpath -rf
+$OSTREE ls -R test2
+# Test checking out a file
+$OSTREE checkout --subpath /baz/saucer test2 checkout-test2-subpath
+assert_file_has_content checkout-test2-subpath/saucer alien
+# Test checking out a file without making a subdir
+mkdir t
+cd t
+$OSTREE checkout --subpath /baz/saucer test2 .
+assert_file_has_content saucer alien
+rm t -rf
 echo "ok checkout subpath"
 
 cd ${test_tmpdir}

tests/test-repo-checkout-subpath.sh

@@ -1,35 +0,0 @@
-#!/bin/bash
-#
-# Copyright (C) 2011,2013 Colin Walters <walters@verbum.org>
-# Copyright (C) 2014 Red Hat, Inc.
-#
-# This library is free software; you can redistribute it and/or
-# modify it under the terms of the GNU Lesser General Public
-# License as published by the Free Software Foundation; either
-# version 2 of the License, or (at your option) any later version.
-#
-# This library is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-# Lesser General Public License for more details.
-#
-# You should have received a copy of the GNU Lesser General Public
-# License along with this library; if not, write to the
-# Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-# Boston, MA 02111-1307, USA.
-
-set -euo pipefail
-
-. $(dirname $0)/libtest.sh
-
-setup_test_repository "bare"
-
-echo '1..1'
-
-repopath=${test_tmpdir}/ostree-srv/gnomerepo
-
-${CMD_PREFIX} ostree --repo=repo checkout -U --subpath=/ test2 checkedout
-
-${CMD_PREFIX} ostree --repo=repo checkout -U --subpath=/firstfile test2 checkedout2
-
-echo "ok"