Merge ~cjwatson/launchpad-buildd:backend-find-empty-output into launchpad-buildd:master

[Colin Watson]

Fix handling of empty output in Backend.find

`Backend.find` mishandled empty output (i.e. if no paths were matched): in that case it returned `['']`. It now correctly returns `[]` instead.

[William Grant (wgrant)]

review: Approve (code)

diff --git a/debian/changelog b/debian/changelog
index 7a5dcb1..cf63e39 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -2,6 +2,7 @@ launchpad-buildd (206) UNRELEASED; urgency=medium
 
   * Fix flake8 violations.
   * Refactor extra status handling to be common to all build types.
+  * Fix handling of empty output in Backend.find.
 
  -- Colin Watson <[e-mail]>  Wed, 08 Dec 2021 15:42:26 +0000
 
diff --git a/lpbuildd/target/backend.py b/lpbuildd/target/backend.py
index a7e778e..fb00dd4 100644
--- a/lpbuildd/target/backend.py
+++ b/lpbuildd/target/backend.py
@@ -146,7 +146,7 @@ class Backend:
         if name is not None:
             cmd.extend(["-name", name])
         cmd.extend(["-printf", "%P\\0"])
-        paths = self.run(cmd, get_output=True).rstrip(b"\0").split(b"\0")
+        paths = self.run(cmd, get_output=True).split(b"\0")[:-1]
         # XXX cjwatson 2017-08-04: Use `os.fsdecode` instead once we're on
         # Python 3.
         return [p.decode("UTF-8") for p in paths]
diff --git a/lpbuildd/target/tests/test_chroot.py b/lpbuildd/target/tests/test_chroot.py
index 8004fa9..10483e1 100644
--- a/lpbuildd/target/tests/test_chroot.py
+++ b/lpbuildd/target/tests/test_chroot.py
@@ -255,6 +255,7 @@ class TestChroot(TestCase):
             {"stdout": io.BytesIO(b"foo\0bar\0")},
             {"stdout": io.BytesIO(b"foo\0bar/bar\0bar/baz\0")},
             {"stdout": io.BytesIO(b"bar\0bar/bar\0")},
+            {"stdout": io.BytesIO(b"")},
             ])
         processes_fixture.add(lambda _: next(test_proc_infos), name="sudo")
         self.assertEqual(
@@ -270,6 +271,9 @@ class TestChroot(TestCase):
         self.assertEqual(
             ["bar", "bar/bar"],
             Chroot("1", "xenial", "amd64").find("/path", name="bar"))
+        self.assertEqual(
+            [],
+            Chroot("1", "xenial", "amd64").find("/path", name="nonexistent"))
 
         find_prefix = [
             "sudo", "/usr/sbin/chroot",
@@ -282,6 +286,7 @@ class TestChroot(TestCase):
             find_prefix + ["-maxdepth", "1"] + find_suffix,
             find_prefix + ["!", "-type", "d"] + find_suffix,
             find_prefix + ["-name", "bar"] + find_suffix,
+            find_prefix + ["-name", "nonexistent"] + find_suffix,
             ]
         self.assertEqual(
             expected_args,
diff --git a/lpbuildd/target/tests/test_lxd.py b/lpbuildd/target/tests/test_lxd.py
index 35be3bb..15b2f1c 100644
--- a/lpbuildd/target/tests/test_lxd.py
+++ b/lpbuildd/target/tests/test_lxd.py
@@ -797,6 +797,7 @@ class TestLXD(TestCase):
             {"stdout": io.BytesIO(b"foo\0bar\0")},
             {"stdout": io.BytesIO(b"foo\0bar/bar\0bar/baz\0")},
             {"stdout": io.BytesIO(b"bar\0bar/bar\0")},
+            {"stdout": io.BytesIO(b"")},
             ])
         processes_fixture.add(lambda _: next(test_proc_infos), name="lxc")
         self.assertEqual(
@@ -812,6 +813,8 @@ class TestLXD(TestCase):
         self.assertEqual(
             ["bar", "bar/bar"],
             LXD("1", "xenial", "amd64").find("/path", name="bar"))
+        self.assertEqual(
+            [], LXD("1", "xenial", "amd64").find("/path", name="nonexistent"))
 
         find_prefix = [
             "lxc", "exec", "lp-xenial-amd64", "--",
@@ -823,6 +826,7 @@ class TestLXD(TestCase):
             find_prefix + ["-maxdepth", "1"] + find_suffix,
             find_prefix + ["!", "-type", "d"] + find_suffix,
             find_prefix + ["-name", "bar"] + find_suffix,
+            find_prefix + ["-name", "nonexistent"] + find_suffix,
             ]
         self.assertEqual(
             expected_args,