Report every editorial attribute in the revision diff

diff_against gained external_url, published_at and user. The view renders
each metadata section only when that attribute changed, and says so once
when none did.

Metadata now precedes the locale pointer, which speaks only of translations:
above the metadata it read as "nothing changed" on a revision that had moved
the page.

2 files changed, 47 insertions, 3 deletions

diff --git a/test/controllers/revisions_controller_test.rb b/test/controllers/revisions_controller_test.rb
index 34f00a4f..d9f49e58 100644
--- a/test/controllers/revisions_controller_test.rb
+++ b/test/controllers/revisions_controller_test.rb
@@ -151,19 +151,35 @@ class RevisionsControllerTest < ActionController::TestCase
     assert_select "input[type='hidden'][name='end_revision'][value='draft']"
   end
 
-  test "diffing two revisions also shows tag, template, and asset changes" do
+  test "diffing shows tag, template, external URL and asset changes" do
     login_as :quentin
     find_or_create_draft(@node, @user)
-    @node.draft.tag_list = "update"
-    @node.draft.save!
+    draft = @node.draft
+    draft.tag_list      = "update"
+    draft.template_name = "title_only"
+    draft.external_url  = "https://example.org/"
+    draft.save!
+    draft.related_assets.create!(:asset => Asset.create!(:name => "diffed",
+                                  :upload_file_name => "diffed.png",
+                                  :upload_content_type => "image/png"))
 
     post(:diff, params: { :node_id => @node.id, :start_revision => @node.pages.first.revision, :end_revision => @node.pages.last.revision })
     assert_response :success
     assert_select "h3", Page.human_attribute_name(:tag_list)
     assert_select "h3", Page.human_attribute_name(:template_name)
+    assert_select "h3", Page.human_attribute_name(:external_url)
     assert_select "h3", Page.human_attribute_name(:assets)
   end
 
+  test "a diff with no metadata changes says so once" do
+    login_as :quentin
+
+    post(:diff, params: { :node_id => @node.id, :start_revision => @node.pages.first.revision, :end_revision => @node.pages.last.revision })
+    assert_response :success
+    assert_select ".diff_meta .diff_unchanged"
+    assert_select ".diff_meta h3", false
+  end
+
   test "revisions#index links back to the node" do
     login_as :quentin
     get :index, params: { :node_id => @node.id }
diff --git a/test/models/page_test.rb b/test/models/page_test.rb
index b737e8b0..f095a7e1 100644
--- a/test/models/page_test.rb
+++ b/test/models/page_test.rb
@@ -302,6 +302,34 @@ class PageTest < ActiveSupport::TestCase
     assert_equal "title_only", diff[:template_name][:to]
   end
 
+  test "diff_against reports external URL, publication date and author changes" do
+    n = Node.root.children.create! :slug => "meta_diff_test"
+    d = find_or_create_draft(n, @user1)
+    d.external_url = "https://old.example.org/"
+    d.published_at = Time.utc(2026, 1, 1, 12, 0, 0)
+    d.save!
+    n.publish_draft!
+
+    new_author = User.where.not(:id => n.head.user_id).first
+    d2 = find_or_create_draft(n, @user1)
+    d2.external_url = "https://new.example.org/"
+    d2.published_at = Time.utc(2026, 3, 1, 12, 0, 0)
+    d2.user         = new_author
+    d2.save!
+
+    diff = d2.diff_against(n.head)
+
+    assert diff[:external_url][:changed]
+    assert_equal "https://old.example.org/", diff[:external_url][:from]
+    assert_equal "https://new.example.org/", diff[:external_url][:to]
+
+    assert diff[:published_at][:changed]
+    assert_equal Time.utc(2026, 3, 1, 12, 0, 0).to_i, diff[:published_at][:to].to_i
+
+    assert diff[:user][:changed]
+    assert_equal new_author.login, diff[:user][:to].login
+  end
+
   test "diff_against reports added and removed assets by filename" do
     n = Node.root.children.create! :slug => "asset_diff_test"
     d = find_or_create_draft(n, @user1)