_project.py: fix the case where a simple string is passed to host-files

also add a test

src/buildstream/_project.py

@@ -764,7 +764,7 @@ def _load_second_pass(self):
         host_files = shell_options.get_sequence("host-files", default=[])
         for host_file in host_files:
             if isinstance(host_file, ScalarNode):
-                mount = HostMount(host_file)
+                mount = HostMount(host_file.as_str())
             else:
                 # Some validation
                 host_file.validate_keys(["path", "host_path", "optional"])

tests/integration/shell.py

@@ -159,7 +159,7 @@ def test_no_shell(cli, datafiles):
 
 
 # Test that bind mounts defined in project.conf work
-@pytest.mark.parametrize("path", [("/etc/pony.conf"), ("/usr/share/pony/pony.txt")])
+@pytest.mark.parametrize("path", [("/etc/pony.conf"), ("/usr/share/pony/pony.txt"), (None)])
 @pytest.mark.datafiles(DATA_DIR)
 @pytest.mark.skipif(not HAVE_SANDBOX, reason="Only available with a functioning sandbox")
 @pytest.mark.xfail(
@@ -169,9 +169,12 @@ def test_no_shell(cli, datafiles):
 def test_host_files(cli, datafiles, path):
     project = str(datafiles)
     ponyfile = os.path.join(project, "files", "shell-mount", "pony.txt")
-    result = execute_shell(
-        cli, project, ["cat", path], config={"shell": {"host-files": [{"host_path": ponyfile, "path": path}]}}
-    )
+    if path is None:
+        result = execute_shell(cli, project, ["cat", ponyfile], config={"shell": {"host-files": [ponyfile]}})
+    else:
+        result = execute_shell(
+            cli, project, ["cat", path], config={"shell": {"host-files": [{"host_path": ponyfile, "path": path}]}}
+        )
     assert result.exit_code == 0
     assert result.output == "pony\n"