Use nested hash data attributes in build_data_attributes method (#530)

Uses the nested hash method of declaring data attributes in
build_data_attributes, as this is what `deep_merge_html_attributes`
expects.

Fixes #529

app/helpers/govuk_link_helper.rb

@@ -188,9 +188,11 @@ def controller_warning_message(value)
 
   def build_data_attributes(data_module, prevent_double_click: nil)
     {
-      "data-module": data_module,
-      "data-prevent-double-click": prevent_double_click
-    }.compact
+      data: {
+        module: data_module,
+        "prevent-double-click": prevent_double_click
+      }.compact
+    }
   end
 end
 

spec/helpers/govuk_link_helper_spec.rb

@@ -181,10 +181,10 @@ def url_for(path)
     end
 
     context "when there are custom attributes" do
-      let(:kwargs) { { lang: "en-GB", dir: "ltr" } }
+      let(:kwargs) { { lang: "en-GB", dir: "ltr", data: { module: "custom-module" } } }
 
       specify "the custom attributes are present on the link" do
-        expect(subject).to have_tag("a", text: "hello", with: { href: "/world", class: "govuk-link", lang: "en-GB", dir: "ltr" })
+        expect(subject).to have_tag("a", text: "hello", with: { href: "/world", class: "govuk-link", lang: "en-GB", dir: "ltr", "data-module": "custom-module" })
       end
     end
 
@@ -314,10 +314,10 @@ def url_for(path)
     end
 
     context "when there are custom attributes" do
-      let(:kwargs) { { lang: "en-GB", dir: "ltr" } }
+      let(:kwargs) { { lang: "en-GB", dir: "ltr", data: { module: "custom-module" } } }
 
       specify "the custom attributes are present on the link" do
-        expect(subject).to have_tag("a", text: "hello", with: { href: "mailto:[email protected]", class: "govuk-link", lang: "en-GB", dir: "ltr" })
+        expect(subject).to have_tag("a", text: "hello", with: { href: "mailto:[email protected]", class: "govuk-link", lang: "en-GB", dir: "ltr", "data-module": "custom-module" })
       end
     end
   end
@@ -502,10 +502,10 @@ def url_for(path)
     end
 
     context "when there are custom attributes" do
-      let(:kwargs) { { lang: "en-GB", dir: "ltr" } }
+      let(:kwargs) { { lang: "en-GB", dir: "ltr", data: { module: "custom-module" } } }
 
       specify "the custom attributes are present on the link" do
-        expect(subject).to have_tag("a", text: "hello", with: { href: "/world", class: "govuk-button", lang: "en-GB", dir: "ltr" })
+        expect(subject).to have_tag("a", text: "hello", with: { href: "/world", class: "govuk-button", lang: "en-GB", dir: "ltr", "data-module": "custom-module" })
       end
     end
   end
@@ -661,7 +661,7 @@ def url_for(path)
     end
 
     context "when there are custom attributes" do
-      let(:kwargs) { { lang: "en-GB", dir: "ltr" } }
+      let(:kwargs) { { lang: "en-GB", dir: "ltr", data: { module: "custom-module" } } }
 
       specify "the custom attributes are present on the button" do
         expect(subject).to have_tag("form", with: { method: "post", action: "/world" }) do
@@ -672,6 +672,7 @@ def url_for(path)
               class: %w[govuk-button],
               dir: "ltr",
               lang: "en-GB",
+              "data-module": "custom-module"
             }
           )
         end