New Context dataclass/subclass mechanism, refs #2127

datasette/__init__.py

@@ -1,6 +1,7 @@
-from datasette.permissions import Permission
+from datasette.permissions import Permission  # noqa
 from datasette.version import __version_info__, __version__  # noqa
 from datasette.utils.asgi import Forbidden, NotFound, Request, Response  # noqa
 from datasette.utils import actor_matches_allow  # noqa
+from datasette.views import Context  # noqa
 from .hookspecs import hookimpl  # noqa
 from .hookspecs import hookspec  # noqa

datasette/app.py

@@ -1,7 +1,8 @@
 import asyncio
-from typing import Sequence, Union, Tuple, Optional, Dict, Iterable
+from typing import Any, Dict, Iterable, List, Optional, Sequence, Tuple, Union
 import asgi_csrf
 import collections
+import dataclasses
 import datetime
 import functools
 import glob
@@ -33,6 +34,7 @@
 from jinja2.environment import Template
 from jinja2.exceptions import TemplateNotFound
 
+from .views import Context
 from .views.base import ureg
 from .views.database import database_download, database_view, TableCreateView
 from .views.index import IndexView
@@ -1115,7 +1117,11 @@ def _register_renderers(self):
             )
 
     async def render_template(
-        self, templates, context=None, request=None, view_name=None
+        self,
+        templates: Union[List[str], str, Template],
+        context: Optional[Union[Dict[str, Any], Context]] = None,
+        request: Optional[Request] = None,
+        view_name: Optional[str] = None,
     ):
         if not self._startup_invoked:
             raise Exception("render_template() called before await ds.invoke_startup()")
@@ -1126,6 +1132,8 @@ async def render_template(
             if isinstance(templates, str):
                 templates = [templates]
             template = self.jinja_env.select_template(templates)
+        if dataclasses.is_dataclass(context):
+            context = dataclasses.asdict(context)
         body_scripts = []
         # pylint: disable=no-member
         for extra_script in pm.hook.extra_body_script(

datasette/views/__init__.py

@@ -0,0 +1,3 @@
+class Context:
+    "Base class for all documented contexts"
+    pass

tests/test_internals_datasette.py

@@ -1,10 +1,12 @@
 """
 Tests for the datasette.app.Datasette class
 """
-from datasette import Forbidden
+import dataclasses
+from datasette import Forbidden, Context
 from datasette.app import Datasette, Database
 from itsdangerous import BadSignature
 import pytest
+from typing import Optional
 
 
 @pytest.fixture
@@ -136,6 +138,22 @@ async def test_datasette_render_template_no_request():
     assert "Error " in rendered
 
 
+@pytest.mark.asyncio
+async def test_datasette_render_template_with_dataclass():
+    @dataclasses.dataclass
+    class ExampleContext(Context):
+        title: str
+        status: int
+        error: str
+
+    context = ExampleContext(title="Hello", status=200, error="Error message")
+    ds = Datasette(memory=True)
+    await ds.invoke_startup()
+    rendered = await ds.render_template("error.html", context)
+    assert "<h1>Hello</h1>" in rendered
+    assert "Error message" in rendered
+
+
 def test_datasette_error_if_string_not_list(tmpdir):
     # https://github.com/simonw/datasette/issues/1985
     db_path = str(tmpdir / "data.db")