load_template() plugin hook

Closes #1042

tests/fixtures.py

@@ -43,6 +43,7 @@ EXPECTED_PLUGINS = [
             "extra_js_urls",
             "extra_template_vars",
             "forbidden",
+            "load_template",
             "menu_links",
             "permission_allowed",
             "prepare_connection",

tests/plugins/my_plugin.py

@@ -308,3 +308,9 @@ def table_actions(datasette, database, table, actor):
             },
             {"href": datasette.urls.instance(), "label": "Table: {}".format(table)},
         ]
+
+
+@hookimpl
+def load_template(template, request):
+    if template == "show_json.html" and request.args.get("_special"):
+        return "<h1>Special show_json: {{ filename }}</h1>"

tests/test_plugins.py

@@ -801,3 +801,8 @@ def test_hook_table_actions(app_client):
         {"label": "Database: fixtures", "href": "/"},
         {"label": "Table: facetable", "href": "/"},
     ]
+
+
+def test_hook_load_template(app_client):
+    response = app_client.get("/-/databases?_special=1")
+    assert response.text == "<h1>Special show_json: databases.json</h1>"