feat(extension): Block on missing required config

charmcraft/extensions/app.py

@@ -114,6 +114,7 @@ def _check_input(self) -> None:
                     f"which conflict with the {self.framework}-framework extension, "
                     "please rename or remove it"
                 )
+        invalid_non_optionals = []
         for config in self._get_nested(self.yaml_data, "config.options"):
             for reserved_config_prefix in ("webserver-", f"{self.framework}-"):
                 if config.startswith(reserved_config_prefix):
@@ -122,6 +123,19 @@ def _check_input(self) -> None:
                         f" reserved configuration prefix {reserved_config_prefix!r}, "
                         "please rename or remove it"
                     )
+            config_option_dict = self._get_nested(
+                self.yaml_data, f"config.options.{config}"
+            )
+            if config_option_dict.get("optional") is False and config_option_dict.get(
+                "default"
+            ):
+                invalid_non_optionals.append(config)
+
+        if invalid_non_optionals:
+            raise ExtensionError(
+                "Non-optional configuration options can not have default values.\n"
+                f"Please either remove the default value or set optional field to true or remove it for the {', '.join(invalid_non_optionals)} configuration option(s)."
+            )
 
     def _get_root_snippet(self) -> dict[str, Any]:
         """Return the root snippet to be merged into the user charmcraft.yaml.

docs/reference/extensions/django-framework-extension.rst

@@ -61,6 +61,8 @@ will set the ``DJANGO_ALLOWED_HOSTS`` environment variable, the ingress
 URL or the Kubernetes service URL if there is no ingress integration,
 will be set automatically.
 
+.. include:: /reuse/reference/extensions/non_optional_config.rst
+
 
 ``peers``, ``provides``, and ``requires`` keys
 ----------------------------------------------

docs/reference/extensions/fastapi-framework-extension.rst

@@ -39,7 +39,9 @@ by running ``juju config <application> token=<token>``.
         token:
           description: The token for the service.
           type: string
-          required: true
+          optional: false
+
+.. include:: /reuse/reference/extensions/non_optional_config.rst
 
 
 ``charmcraft.yaml`` > ``peers``, ``provides``, ``requires``

docs/reference/extensions/flask-framework-extension.rst

@@ -37,6 +37,8 @@ charm can set it by running ``juju config <application> token=<token>``.
           description: The token for the service.
           type: string
 
+.. include:: /reuse/reference/extensions/non_optional_config.rst
+
 
 ``charmcraft.yaml`` > ``peers``, ``provides``, ``requires``
 -----------------------------------------------------------

docs/reference/extensions/go-framework-extension.rst

@@ -48,6 +48,8 @@ charm can set it by running ``juju config <application> token=<token>``.
           description: The token for the service.
           type: string
 
+.. include:: /reuse/reference/extensions/non_optional_config.rst
+
 
 ``charmcraft.yaml`` > ``peers``, ``provides``, ``requires``
 -----------------------------------------------------------

docs/reuse/reference/extensions/non_optional_config.rst

@@ -0,0 +1,22 @@
+
+In addition to this, you can set the configuration option to be
+mandatory by setting the ``optional`` key to ``false``. This will
+block the charm and stop services until the configuration is supplied. For example,
+if your application needs an ``api-token`` to function correctly you can set
+``optional``, as shown below. This will block the charm and stop the
+services until the ``api-token`` configuration is supplied.
+
+.. code-block:: yaml
+    :caption: charmcraft.yaml
+
+    config:
+      options:
+        api-token:
+          description: The token necessary for the service to run.
+          type: string
+          optional: false
+
+.. note::
+
+    A configuration with ``optional: false`` can't also have a ``default`` key.
+    If it has both, the charm will fail to pack.

tests/extensions/test_app.py

@@ -24,6 +24,16 @@
     GoFramework,
 )
 
+NON_OPTIONAL_OPTIONS = {
+    "options": {
+        "non-optional-string": {
+            "description": "Example of a non-optional string configuration option.",
+            "type": "string",
+            "optional": False,
+        }
+    }
+}
+
 
 def make_flask_input_yaml():
     return {
@@ -33,6 +43,7 @@ def make_flask_input_yaml():
         "description": "test description",
         "bases": [{"name": "ubuntu", "channel": "22.04"}],
         "extensions": ["flask-framework"],
+        "config": NON_OPTIONAL_OPTIONS,
     }
 
 
@@ -69,7 +80,10 @@ def flask_input_yaml_fixture():
                     {"lib": "tempo_coordinator_k8s.tracing", "version": "0"},
                 ],
                 "config": {
-                    "options": {**FlaskFramework.options},
+                    "options": {
+                        **FlaskFramework.options,
+                        **NON_OPTIONAL_OPTIONS["options"],
+                    },
                 },
                 "parts": {
                     "charm": {
@@ -114,6 +128,7 @@ def flask_input_yaml_fixture():
                     "s390x": None,
                 },
                 "extensions": ["django-framework"],
+                "config": NON_OPTIONAL_OPTIONS,
             },
             False,
             {
@@ -146,7 +161,10 @@ def flask_input_yaml_fixture():
                     {"lib": "tempo_coordinator_k8s.tracing", "version": "0"},
                 ],
                 "config": {
-                    "options": {**DjangoFramework.options},
+                    "options": {
+                        **DjangoFramework.options,
+                        **NON_OPTIONAL_OPTIONS["options"],
+                    },
                 },
                 "parts": {
                     "charm": {
@@ -186,6 +204,7 @@ def flask_input_yaml_fixture():
                     "amd64": None,
                 },
                 "extensions": ["go-framework"],
+                "config": NON_OPTIONAL_OPTIONS,
             },
             True,
             {
@@ -213,7 +232,10 @@ def flask_input_yaml_fixture():
                     {"lib": "tempo_coordinator_k8s.tracing", "version": "0"},
                 ],
                 "config": {
-                    "options": {**GoFramework.options},
+                    "options": {
+                        **GoFramework.options,
+                        **NON_OPTIONAL_OPTIONS["options"],
+                    },
                 },
                 "parts": {
                     "charm": {
@@ -253,6 +275,7 @@ def flask_input_yaml_fixture():
                     "amd64": None,
                 },
                 "extensions": ["fastapi-framework"],
+                "config": NON_OPTIONAL_OPTIONS,
             },
             True,
             {
@@ -280,7 +303,10 @@ def flask_input_yaml_fixture():
                     {"lib": "tempo_coordinator_k8s.tracing", "version": "0"},
                 ],
                 "config": {
-                    "options": {**FastAPIFramework.options},
+                    "options": {
+                        **FastAPIFramework.options,
+                        **NON_OPTIONAL_OPTIONS["options"],
+                    },
                 },
                 "parts": {
                     "charm": {
@@ -404,6 +430,20 @@ def test_flask_merge_charm_libs(flask_input_yaml, tmp_path):
         {"config": {"options": {"flask-foobar": {"type": "string"}}}},
         id="reserved-config-prefix-flask",
     ),
+    pytest.param(
+        {
+            "config": {
+                "options": {
+                    "non-optional": {
+                        "type": "string",
+                        "optional": False,
+                        "default": "default value",
+                    }
+                }
+            }
+        },
+        id="non-optional-config-with-default",
+    ),
 ]