Correctly persist selected facets in hidden fields

Closes #963

datasette/templates/table.html

@@ -88,9 +88,6 @@
             </div>
             <label class="sort_by_desc small-screen-only"><input type="checkbox" name="_sort_by_desc"{% if sort_desc %} checked{% endif %}> descending</label>
         {% endif %}
-        {% for facet in sorted_facet_results %}
-            <input type="hidden" name="_facet" value="{{ facet.name }}">
-        {% endfor %}
         {% for key, value in form_hidden_args %}
             <input type="hidden" name="{{ key }}" value="{{ value }}">
         {% endfor %}

datasette/views/table.py

@@ -778,6 +778,12 @@ class TableView(RowTableShared):
             )
             self.ds.update_with_inherited_metadata(metadata)
             form_hidden_args = []
+            # Add currently selected facets
+            for arg in special_args:
+                if arg == "_facet" or arg.startswith("_facet_"):
+                    form_hidden_args.extend(
+                        (arg, item) for item in request.args.getlist(arg)
+                    )
             for arg in ("_fts_table", "_fts_pk"):
                 if arg in special_args:
                     form_hidden_args.append((arg, special_args[arg]))

tests/test_html.py

@@ -448,12 +448,16 @@ def test_facet_display(app_client):
 
 
 def test_facets_persist_through_filter_form(app_client):
-    response = app_client.get("/fixtures/facetable?_facet=planet_int&_facet=city_id")
+    response = app_client.get(
+        "/fixtures/facetable?_facet=planet_int&_facet=city_id&_facet_array=tags"
+    )
     assert response.status == 200
     inputs = Soup(response.body, "html.parser").find("form").findAll("input")
     hiddens = [i for i in inputs if i["type"] == "hidden"]
-    assert [("_facet", "city_id"), ("_facet", "planet_int")] == [
-        (hidden["name"], hidden["value"]) for hidden in hiddens
+    assert [(hidden["name"], hidden["value"]) for hidden in hiddens] == [
+        ("_facet", "planet_int"),
+        ("_facet", "city_id"),
+        ("_facet_array", "tags"),
     ]