sync: Fix sorting for nested projects

The current logic to create checkout layers doesn't work in all cases.
For example, let's assume there are three projects: "foo", "foo/bar" and
"foo-bar". Sorting lexicographical order is incorrect as foo-bar would
be placed between foo and foo/bar, breaking layering logic.

Instead, we split filepaths based using path delimiter (always /) and
then use lexicographical sort.

BUG=b:325119758
TEST=./run_tests, manual sync on chromiumos repository

Change-Id: I76924c3cc6ba2bb860d7a3e48406a6bba8f58c10
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/412338
Tested-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: George Engelbrecht <engeg@google.com>

tests/test_subcmds_sync.py

@@ -304,29 +304,54 @@ class LocalSyncState(unittest.TestCase):
         self.assertEqual(self.state.GetFetchTime(projA), 5)
 
 
+class FakeProject:
+    def __init__(self, relpath):
+        self.relpath = relpath
+
+    def __str__(self):
+        return f"project: {self.relpath}"
+
+    def __repr__(self):
+        return str(self)
+
+
 class SafeCheckoutOrder(unittest.TestCase):
     def test_no_nested(self):
-        p_f = mock.MagicMock(relpath="f")
-        p_foo = mock.MagicMock(relpath="foo")
+        p_f = FakeProject("f")
+        p_foo = FakeProject("foo")
         out = sync._SafeCheckoutOrder([p_f, p_foo])
         self.assertEqual(out, [[p_f, p_foo]])
 
     def test_basic_nested(self):
-        p_foo = p_foo = mock.MagicMock(relpath="foo")
-        p_foo_bar = mock.MagicMock(relpath="foo/bar")
+        p_foo = p_foo = FakeProject("foo")
+        p_foo_bar = FakeProject("foo/bar")
         out = sync._SafeCheckoutOrder([p_foo, p_foo_bar])
         self.assertEqual(out, [[p_foo], [p_foo_bar]])
 
     def test_complex_nested(self):
-        p_foo = mock.MagicMock(relpath="foo")
-        p_foo_bar = mock.MagicMock(relpath="foo/bar")
-        p_foo_bar_baz_baq = mock.MagicMock(relpath="foo/bar/baz/baq")
-        p_bar = mock.MagicMock(relpath="bar")
+        p_foo = FakeProject("foo")
+        p_foobar = FakeProject("foobar")
+        p_foo_dash_bar = FakeProject("foo-bar")
+        p_foo_bar = FakeProject("foo/bar")
+        p_foo_bar_baz_baq = FakeProject("foo/bar/baz/baq")
+        p_bar = FakeProject("bar")
         out = sync._SafeCheckoutOrder(
-            [p_foo_bar_baz_baq, p_foo, p_foo_bar, p_bar]
+            [
+                p_foo_bar_baz_baq,
+                p_foo,
+                p_foobar,
+                p_foo_dash_bar,
+                p_foo_bar,
+                p_bar,
+            ]
         )
         self.assertEqual(
-            out, [[p_bar, p_foo], [p_foo_bar], [p_foo_bar_baz_baq]]
+            out,
+            [
+                [p_bar, p_foo, p_foo_dash_bar, p_foobar],
+                [p_foo_bar],
+                [p_foo_bar_baz_baq],
+            ],
         )