Use Jinja async mode, refs #628

datasette/app.py

@@ -583,7 +583,9 @@ class Datasette:
                 ),
             ]
         )
-        self.jinja_env = Environment(loader=template_loader, autoescape=True)
+        self.jinja_env = Environment(
+            loader=template_loader, autoescape=True, enable_async=True
+        )
         self.jinja_env.filters["escape_css_string"] = escape_css_string
         self.jinja_env.filters["quote_plus"] = lambda u: urllib.parse.quote_plus(u)
         self.jinja_env.filters["escape_sqlite"] = escape_sqlite
@@ -730,5 +732,5 @@ class DatasetteRouter(AsgiRouter):
         else:
             template = self.ds.jinja_env.select_template(templates)
             await asgi_send_html(
-                send, template.render(info), status=status, headers=headers
+                send, await template.render_async(info), status=status, headers=headers
             )

datasette/views/base.py

@@ -139,7 +139,7 @@ class BaseView(AsgiView):
             extra_template_vars.update(extra_vars)
 
         return Response.html(
-            template.render(
+            await template.render_async(
                 {
                     **context,
                     **{

tests/fixtures.py

@@ -446,13 +446,19 @@ def render_cell(value, database):
 
 @hookimpl
 def extra_template_vars(template, database, table, view_name, request, datasette):
+    async def query_database(sql):
+        first_db = list(datasette.databases.keys())[0]
+        return (
+            await datasette.execute(first_db, sql)
+        ).rows[0][0]
     async def inner():
         return {
             "extra_template_vars_from_awaitable": json.dumps({
                 "template": template,
                 "scope_path": request.scope["path"],
                 "awaitable": True,
-            }, default=lambda b: b.decode("utf8"))
+            }, default=lambda b: b.decode("utf8")),
+            "query_database": query_database,
         }
     return inner
 

tests/test_plugins.py

@@ -1,5 +1,6 @@
 from bs4 import BeautifulSoup as Soup
 from .fixtures import app_client, make_app_client, TEMP_PLUGIN_SECRET_FILE  # noqa
+from datasette.utils import sqlite3
 import base64
 import json
 import os
@@ -214,3 +215,20 @@ def test_plugins_extra_template_vars(restore_working_directory):
             "awaitable": True,
             "scope_path": "/-/metadata",
         } == extra_template_vars_from_awaitable
+
+
+def test_plugins_async_template_function(restore_working_directory):
+    for client in make_app_client(
+        template_dir=str(pathlib.Path(__file__).parent / "test_templates")
+    ):
+        response = client.get("/-/metadata")
+        assert response.status == 200
+        extra_from_awaitable_function = (
+            Soup(response.body, "html.parser")
+            .select("pre.extra_from_awaitable_function")[0]
+            .text
+        )
+        expected = (
+            sqlite3.connect(":memory:").execute("select sqlite_version()").fetchone()[0]
+        )
+        assert expected == extra_from_awaitable_function

tests/test_templates/show_json.html

@@ -5,4 +5,5 @@
 Test data for extra_template_vars:
 <pre class="extra_template_vars">{{ extra_template_vars|safe }}</pre>
 <pre class="extra_template_vars_from_awaitable">{{ extra_template_vars_from_awaitable|safe }}</pre>
+<pre class="extra_from_awaitable_function">{{ query_database("select sqlite_version();") }}</pre>
 {% endblock %}