RowContext - row page now renders a documented Context dataclass

RowView declares context_class = RowContext; BaseView.render()
constructs the dataclass from the assembled context, dropping any keys
not declared on the class, after select_templates and
alternate_url_json have been added. Extras-named fields use
extra_field() so their documentation comes from the Extra classes;
view-added fields carry help metadata next to the view code.

Refs #2127

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

datasette/views/base.py

@@ -1,5 +1,6 @@
 import asyncio
 import csv
+import dataclasses
 import hashlib
 import sys
 import textwrap
@@ -88,6 +89,9 @@ class View:
 class BaseView:
     ds = None
     has_json_alternate = True
+    # Set to a Context subclass to render a documented template context -
+    # keys not declared on the class are dropped before rendering
+    context_class = None
 
     def __init__(self, datasette):
         self.ds = datasette
@@ -169,6 +173,11 @@ class BaseView:
                     )
                 }
             )
+        if self.context_class is not None:
+            declared = {f.name for f in dataclasses.fields(self.context_class)}
+            template_context = self.context_class(
+                **{k: v for k, v in template_context.items() if k in declared}
+            )
         return Response.html(
             await self.ds.render_template(
                 template,

datasette/views/row.py

@@ -11,16 +11,95 @@ from datasette.utils import (
     escape_sqlite,
 )
 from datasette.plugins import pm
+from dataclasses import dataclass, field
 import json
 import markupsafe
 import sqlite_utils
-from datasette.extras import extra_names_from_request
+from datasette.extras import extra_names_from_request, ExtraScope
+from . import Context, extra_field
 from .table import display_columns_and_rows
 from .table_extras import RowExtraContext, resolve_row_extras, table_extra_registry
 
 
+@dataclass
+class RowContext(Context):
+    "The page showing an individual row, e.g. /fixtures/facetable/1"
+
+    extras_scope = ExtraScope.ROW
+
+    # Fields resolved by registered extras - their documentation comes
+    # from the description on each Extra class in table_extras.py
+    columns: list = extra_field()
+    database: str = extra_field()
+    database_color: str = extra_field()
+    foreign_key_tables: list = extra_field()
+    metadata: dict = extra_field()
+    primary_keys: list = extra_field()
+    private: bool = extra_field()
+    table: str = extra_field()
+
+    # Fields added by the view code
+    ok: bool = field(
+        metadata={"help": "True if the data for this page was retrieved without errors"}
+    )
+    rows: list = field(
+        metadata={
+            "help": "The rows for this page, as a list of dictionaries mapping column name to value"
+        }
+    )
+    primary_key_values: list = field(
+        metadata={"help": "Values of the primary keys for this row, from the URL"}
+    )
+    query_ms: float = field(
+        metadata={
+            "help": "Time taken by the SQL queries for this page, in milliseconds"
+        }
+    )
+    display_columns: list = field(
+        metadata={"help": "Column objects formatted for the HTML table display"}
+    )
+    display_rows: list = field(
+        metadata={"help": "Row data formatted for the HTML table display"}
+    )
+    custom_table_templates: list = field(
+        metadata={
+            "help": "Custom template names that were considered for displaying this table"
+        }
+    )
+    row_actions: list = field(
+        metadata={"help": "Row actions made available by plugin hooks"}
+    )
+    top_row: callable = field(
+        metadata={"help": "Async function rendering the top_row plugin slot"}
+    )
+    renderers: dict = field(
+        metadata={
+            "help": "Dictionary mapping output format names (e.g. json) to their URLs for this page"
+        }
+    )
+    url_csv: str = field(metadata={"help": "URL for the CSV export of this page"})
+    url_csv_path: str = field(metadata={"help": "Path portion of the CSV export URL"})
+    url_csv_hidden_args: list = field(
+        metadata={
+            "help": "(name, value) pairs for hidden form fields used by the CSV export form"
+        }
+    )
+    settings: dict = field(
+        metadata={"help": "Dictionary of Datasette's current settings"}
+    )
+    select_templates: list = field(
+        metadata={
+            "help": "List of template names that were considered for this page, the one used marked with an asterisk"
+        }
+    )
+    alternate_url_json: str = field(
+        metadata={"help": "URL for the JSON version of this page"}
+    )
+
+
 class RowView(DataView):
     name = "row"
+    context_class = RowContext
 
     async def data(self, request, default_labels=False):
         resolved = await self.ds.resolve_row(request)

tests/test_template_context.py

@@ -186,6 +186,14 @@ def test_table_context_fields_match_documented_contract():
     }
 
 
+def test_row_context_fields_match_documented_contract():
+    from datasette.views.row import RowContext
+
+    assert {f.name for f in RowContext.documented_fields()} == {
+        key.name for key in PAGES["row"].documented_keys()
+    }
+
+
 def test_base_context_keys_all_have_docs():
     for key in BASE_CONTEXT_KEYS:
         assert key.doc, "Base context key {} is missing docs".format(key.name)