Allow search autocomplete to be easily disabled

Autocomplete uses a denylist to stop certain terms from serving
suggestions. The process to update the denylist is very manual and
developer heavy.

It might be difficult to update the denylist over the holiday period. In
that situation the decision might be taken to temporarily turn off
autocomplete entirely.

An environment variable is used to determine whether or not to render
search with autocomplete. The value of this variable will be applied
globally across all applications that use site search.

This environment variable will either exist, or not. The value of it
doesn't really matter. If it exists, then search with autocomplete
should be disabled. A value of "1" is used in the tests, as that is the
default value being set in the helm charts.

See alphagov/govuk-helm-charts#2832

app/controllers/finders_controller.rb

@@ -58,6 +58,7 @@ def show_page_variables
     @sort_presenter = sort_presenter
     @pagination = pagination_presenter
     @spelling_suggestion_presenter = spelling_suggestion_presenter
+    @search_component = use_autocomplete? ? "search_with_autocomplete" : "search"
   end
 
 private
@@ -386,4 +387,8 @@ def filter_query_array(arr)
       arr.reject { |v| v == "all" }.compact.presence
     end
   end
+
+  def use_autocomplete?
+    true unless ENV["GOVUK_DISABLE_SEARCH_AUTOCOMPLETE"]
+  end
 end

app/views/finders/show_all_content_finder.html.erb

@@ -53,7 +53,7 @@
     <div class="govuk-grid-row">
       <div class="govuk-grid-column-two-thirds-from-desktop">
         <div id="keywords" role="search" aria-label="Sitewide">
-          <%= render "govuk_publishing_components/components/search_with_autocomplete", {
+          <%= render "govuk_publishing_components/components/#{@search_component}", {
             id: "finder-keyword-search",
             name: "keywords",
             type: 'search',

spec/controllers/finders_controller_spec.rb

@@ -251,6 +251,24 @@
         expect(response.status).to eq(200)
         expect(response).to render_template("finders/show_all_content_finder")
       end
+
+      describe "search autocomplete" do
+        it "renders the search autocomplete when enabled" do
+          ClimateControl.modify GOVUK_DISABLE_SEARCH_AUTOCOMPLETE: nil do
+            get :show, params: { slug: "search/all", keywords: "hello" }
+
+            expect(response.body).to include("gem-c-search-with-autocomplete")
+          end
+        end
+
+        it "does not render the autocomplete when disabled" do
+          ClimateControl.modify GOVUK_DISABLE_SEARCH_AUTOCOMPLETE: "1" do
+            get :show, params: { slug: "search/all", keywords: "hello" }
+
+            expect(response.body).not_to include("gem-c-search-with-autocomplete")
+          end
+        end
+      end
     end
   end