feat: extensions (#1009)

* feat: extensions

* refactor: remove support for passing in extensions as instances

src/django_components/app_settings.py

@@ -1,6 +1,7 @@
 import re
 from dataclasses import dataclass
 from enum import Enum
+from importlib import import_module
 from os import PathLike
 from pathlib import Path
 from typing import (
@@ -15,6 +16,7 @@ from typing import (
     Optional,
     Sequence,
     Tuple,
+    Type,
     TypeVar,
     Union,
     cast,
@@ -25,6 +27,7 @@ from django.conf import settings
 from django_components.util.misc import default
 
 if TYPE_CHECKING:
+    from django_components.extension import ComponentExtension
     from django_components.tag_formatter import TagFormatterABC
 
 
@@ -146,6 +149,25 @@ class ComponentsSettings(NamedTuple):
     ```
     """
 
+    extensions: Optional[Sequence[Union[Type["ComponentExtension"], str]]] = None
+    """
+    List of [extensions](../../concepts/advanced/extensions) to be loaded.
+
+    The extensions can be specified as:
+
+    - Python import path, e.g. `"path.to.my_extension.MyExtension"`.
+    - Extension class, e.g. `my_extension.MyExtension`.
+
+    ```python
+    COMPONENTS = ComponentsSettings(
+        extensions=[
+            "path.to.my_extension.MyExtension",
+            StorybookExtension,
+        ],
+    )
+    ```
+    """
+
     autodiscover: Optional[bool] = None
     """
     Toggle whether to run [autodiscovery](../../concepts/fundamentals/autodiscovery) at the Django server startup.
@@ -647,6 +669,7 @@ defaults = ComponentsSettings(
     debug_highlight_components=False,
     debug_highlight_slots=False,
     dynamic_component_name="dynamic",
+    extensions=[],
     libraries=[],  # E.g. ["mysite.components.forms", ...]
     multiline_tags=True,
     reload_on_file_change=False,
@@ -709,6 +732,9 @@ class InternalSettings:
                 components_settings.dynamic_component_name, defaults.dynamic_component_name
             ),
             libraries=default(components_settings.libraries, defaults.libraries),
+            # NOTE: Internally we store the extensions as a list of instances, but the user
+            #       can pass in either a list of classes or a list of import strings.
+            extensions=self._prepare_extensions(components_settings),  # type: ignore[arg-type]
             multiline_tags=default(components_settings.multiline_tags, defaults.multiline_tags),
             reload_on_file_change=self._prepare_reload_on_file_change(components_settings),
             template_cache_size=default(components_settings.template_cache_size, defaults.template_cache_size),
@@ -718,6 +744,33 @@ class InternalSettings:
             tag_formatter=default(components_settings.tag_formatter, defaults.tag_formatter),  # type: ignore[arg-type]
         )
 
+    def _prepare_extensions(self, new_settings: ComponentsSettings) -> List["ComponentExtension"]:
+        extensions: Sequence[Union[Type["ComponentExtension"], str]] = default(
+            new_settings.extensions, cast(List[str], defaults.extensions)
+        )
+
+        # Prepend built-in extensions
+        from django_components.extensions.view import ViewExtension
+
+        extensions = [ViewExtension] + list(extensions)
+
+        # Extensions may be passed in either as classes or import strings.
+        extension_instances: List["ComponentExtension"] = []
+        for extension in extensions:
+            if isinstance(extension, str):
+                import_path, class_name = extension.rsplit(".", 1)
+                extension_module = import_module(import_path)
+                extension = cast(Type["ComponentExtension"], getattr(extension_module, class_name))
+
+            if isinstance(extension, type):
+                extension_instance = extension()
+            else:
+                extension_instances.append(extension)
+
+            extension_instances.append(extension_instance)
+
+        return extension_instances
+
     def _prepare_reload_on_file_change(self, new_settings: ComponentsSettings) -> bool:
         val = new_settings.reload_on_file_change
         # TODO_REMOVE_IN_V1
@@ -780,6 +833,10 @@ class InternalSettings:
     def LIBRARIES(self) -> List[str]:
         return self._settings.libraries  # type: ignore[return-value]
 
+    @property
+    def EXTENSIONS(self) -> List["ComponentExtension"]:
+        return self._settings.extensions  # type: ignore[return-value]
+
     @property
     def MULTILINE_TAGS(self) -> bool:
         return self._settings.multiline_tags  # type: ignore[return-value]