fix(storage): handle manifest without backend config

sunbeam-python/sunbeam/storage/steps.py

@@ -303,7 +303,8 @@ def prompt(
                 if crt := backends.root.get(self.backend_name):
                     # Since question generation depends on field name,
                     # do not dump by alias
-                    preseed = crt.model_dump(by_alias=False)["config"]
+                    if crt.config is not None:
+                        preseed = crt.config.model_dump(by_alias=False)
 
         # Preseed from user is higher priority than manifest
         preseed.update(self.preseed)

sunbeam-python/tests/unit/sunbeam/storage/test_base.py

@@ -279,6 +279,12 @@ def test_remove_backend(self, backend, mock_deployment, mock_console, tmp_path):
     def test_build_terraform_vars(self, backend, mock_deployment, mock_manifest):
         """Test Terraform variables generation."""
         backend_name = "test-backend"
+        charm_manifest = Mock(channel="latest/edge", revision=None)
+        backend_manifest = Mock()
+        backend_manifest.software.charms = {backend.charm_name: charm_manifest}
+        mock_manifest.storage.root = {
+            backend.backend_type: Mock(root={backend_name: backend_manifest})
+        }
         config = backend.config_type().model_validate(
             {
                 "required-field": "test",
@@ -294,7 +300,7 @@ def test_build_terraform_vars(self, backend, mock_deployment, mock_manifest):
         assert tfvars["principal_application"] == backend.principal_application
         assert "charm_name" in tfvars
         assert tfvars["charm_name"] == backend.charm_name
-        assert "charm_channel" in tfvars
+        assert tfvars["charm_channel"] == "latest/edge"
         assert "charm_base" in tfvars
         assert "endpoint_bindings" in tfvars
         assert "charm_config" in tfvars

sunbeam-python/tests/unit/sunbeam/storage/test_steps.py

@@ -12,6 +12,7 @@
 from sunbeam.core.steps import DeployMachineApplicationStep
 from sunbeam.storage.models import SecretDictField
 from sunbeam.storage.steps import (
+    BaseStorageBackendDeployStep,
     DeploySpecificCinderVolumeStep,
     basemodel_validator,
     generate_questions_from_config,
@@ -103,6 +104,98 @@ def test_optional_questions_include_validation(self):
             optional_question.validation_function(-1)  # type: ignore[arg-type]
 
 
+class TestBaseStorageBackendDeployStep:
+    """Tests for the base storage backend deployment step."""
+
+    @pytest.fixture
+    def deploy_step(
+        self,
+        basic_deployment,
+        basic_client,
+        basic_tfhelper,
+        basic_jhelper,
+        basic_manifest,
+        mock_backend,
+        test_model,
+    ):
+        """Create a base storage backend deployment step."""
+        return BaseStorageBackendDeployStep(
+            basic_deployment,
+            basic_client,
+            basic_tfhelper,
+            basic_jhelper,
+            basic_manifest,
+            {
+                "required_field": "cli-value",
+                "secret_field": "cli-secret",
+            },
+            "test-backend",
+            mock_backend,
+            test_model,
+        )
+
+    def test_prompt_without_manifest_config(
+        self, deploy_step, basic_manifest, mock_backend
+    ):
+        """CLI configuration is used when manifest config is absent."""
+        backend_manifest = Mock(config=None)
+        basic_manifest.storage.root = {
+            mock_backend.backend_type: Mock(
+                root={deploy_step.backend_name: backend_manifest}
+            )
+        }
+
+        with (
+            patch("sunbeam.storage.steps.load_answers", return_value={}),
+            patch("sunbeam.storage.steps.QuestionBank") as question_bank,
+            patch("sunbeam.storage.steps.ConfirmQuestion") as confirm_question,
+            patch("sunbeam.storage.steps.write_answers"),
+        ):
+            question_bank.return_value.questions = {}
+            confirm_question.return_value.ask.return_value = False
+
+            deploy_step.prompt()
+
+        assert question_bank.call_args.kwargs["preseed"] == {
+            "required_field": "cli-value",
+            "secret_field": "cli-secret",
+        }
+
+    def test_prompt_cli_config_overrides_manifest_config(
+        self, deploy_step, basic_manifest, mock_backend
+    ):
+        """CLI configuration takes precedence over manifest configuration."""
+        manifest_config = mock_backend.config_type().model_validate(
+            {
+                "required-field": "manifest-value",
+                "secret-field": "manifest-secret",
+                "optional-field": "manifest-optional",
+            }
+        )
+        backend_manifest = Mock(config=manifest_config)
+        basic_manifest.storage.root = {
+            mock_backend.backend_type: Mock(
+                root={deploy_step.backend_name: backend_manifest}
+            )
+        }
+
+        with (
+            patch("sunbeam.storage.steps.load_answers", return_value={}),
+            patch("sunbeam.storage.steps.QuestionBank") as question_bank,
+            patch("sunbeam.storage.steps.ConfirmQuestion") as confirm_question,
+            patch("sunbeam.storage.steps.write_answers"),
+        ):
+            question_bank.return_value.questions = {}
+            confirm_question.return_value.ask.return_value = False
+
+            deploy_step.prompt()
+
+        preseed = question_bank.call_args.kwargs["preseed"]
+        assert preseed["required_field"] == "cli-value"
+        assert preseed["secret_field"] == "cli-secret"
+        assert preseed["optional_field"] == "manifest-optional"
+
+
 class TestDeploySpecificCinderVolumeStep:
     """Tests for DeploySpecificCinderVolumeStep class."""