Add autocomplete to search index

We've tried to add autocomplete to each site search input on GOV.UK.
When reviewing this we noticed that one of them was missed, the one on
https://www.gov.uk/search.

This commit corrects this by adding the component here.

app/views/search/_search_field.html.erb

@@ -6,12 +6,14 @@
 } %>
 <% end %>
 
-<%= render "govuk_publishing_components/components/search", {
+<%= render "govuk_publishing_components/components/#{search_component}", {
   inline_label: false,
   label_text: label_text,
   size: "large",
   id: "search-main",
   disable_corrections: true,
+  source_url: api_search_autocomplete_url(format: :json),
+  source_key: "suggestions",
 } %>
 
 <%= hidden_field_tag("filter_manual[]", params[:filter_manual]) if params[:filter_manual] %>

spec/controllers/search_controller_spec.rb

@@ -36,5 +36,26 @@
         expect(response).to redirect_to(destination)
       end
     end
+
+    context "when GOVUK_DISABLE_SEARCH_AUTOCOMPLETE is not set" do
+      it "renders the search autocomplete component" do
+        ClimateControl.modify GOVUK_DISABLE_SEARCH_AUTOCOMPLETE: nil do
+          get :index
+
+          expect(response.body).to include("gem-c-search-with-autocomplete")
+        end
+      end
+    end
+
+    context "when GOVUK_DISABLE_SEARCH_AUTOCOMPLETE is set" do
+      it "renders the search component instead of the autocomplete component" do
+        ClimateControl.modify GOVUK_DISABLE_SEARCH_AUTOCOMPLETE: "1" do
+          get :index
+
+          expect(response.body).not_to include("gem-c-search-with-autocomplete")
+          expect(response.body).to include("gem-c-search")
+        end
+      end
+    end
   end
 end