Chore(extension): Implementation, test and docs.

Author: alithethird

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 +61,28 @@ 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.
 
+In addition to this, you can set the configuration options to be
+``non-optional`` by setting the ``optional`` key to ``False``. This will
+block the charm and stop services until the config is supplied. For example,
+if your application needs an ``api-token`` to function correctly you can set
+it ``non-optional``, as below. This will block the charm and stop the
+services until the ``api-token`` is supplied.
+
+.. code-block:: yaml
+
+    config:
+      options:
+        api-token:
+          description: The token necessary for the service to run.
+          type: string
+          optional: false
+
+.. note::
+
+    The ``non-optional`` options can not have ``default`` values. If you
+    set a ``default`` value to a ``non-optional`` configuration option
+    ``charmcraft`` will fail when packing the charm.
+
 
 ``peers``, ``provides``, and ``requires`` keys
 ----------------------------------------------

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

@@ -39,7 +39,29 @@ by running ``juju config <application> token=<token>``.
         token:
           description: The token for the service.
           type: string
-          required: true
+          optional: false
+
+In addition to this, you can set the configuration options to be
+``non-optional`` by setting the ``optional`` key to ``False``. This will
+block the charm and stop services until the config is supplied. For example,
+if your application needs an ``api-token`` to function correctly you can set
+it ``non-optional``, as below. This will block the charm and stop the
+services until the ``api-token`` is supplied.
+
+.. code-block:: yaml
+
+    config:
+      options:
+        api-token:
+          description: The token necessary for the service to run.
+          type: string
+          optional: false
+
+.. note::
+
+    The ``non-optional`` options can not have ``default`` values. If you
+    set a ``default`` value to a ``non-optional`` configuration option
+    ``charmcraft`` will fail when packing the charm.
 
 
 ``charmcraft.yaml`` > ``peers``, ``provides``, ``requires``

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

@@ -37,6 +37,28 @@ charm can set it by running ``juju config <application> token=<token>``.
           description: The token for the service.
           type: string
 
+In addition to this, you can set the configuration options to be
+``non-optional`` by setting the ``optional`` key to ``False``. This will
+block the charm and stop services until the config is supplied. For example,
+if your application needs an ``api-token`` to function correctly you can set
+it ``non-optional``, as below. This will block the charm and stop the
+services until the ``api-token`` is supplied.
+
+.. code-block:: yaml
+
+    config:
+      options:
+        api-token:
+          description: The token necessary for the service to run.
+          type: string
+          optional: false
+
+.. note::
+
+    The ``non-optional`` options can not have ``default`` values. If you
+    set a ``default`` value to a ``non-optional`` configuration option
+    ``charmcraft`` will fail when packing the charm.
+
 
 ``charmcraft.yaml`` > ``peers``, ``provides``, ``requires``
 -----------------------------------------------------------

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

@@ -48,6 +48,28 @@ charm can set it by running ``juju config <application> token=<token>``.
           description: The token for the service.
           type: string
 
+In addition to this, you can set the configuration options to be
+``non-optional`` by setting the ``optional`` key to ``False``. This will
+block the charm and stop services until the config is supplied. For example,
+if your application needs an ``api-token`` to function correctly you can set
+it ``non-optional``, as below. This will block the charm and stop the
+services until the ``api-token`` is supplied.
+
+.. code-block:: yaml
+
+    config:
+      options:
+        api-token:
+          description: The token necessary for the service to run.
+          type: string
+          optional: false
+
+.. note::
+
+    The ``non-optional`` options can not have ``default`` values. If you
+    set a ``default`` value to a ``non-optional`` configuration option
+    ``charmcraft`` will fail when packing the charm.
+
 
 ``charmcraft.yaml`` > ``peers``, ``provides``, ``requires``
 -----------------------------------------------------------

tests/extensions/test_app.py

@@ -404,6 +404,20 @@ 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-defautl",
+    ),
 ]