Spike out adding custom error messages via locales

app/components/admin/error_summary_component.rb

@@ -27,7 +27,7 @@ def humanized_class_name
   def error_items
     errors.map do |error|
       error_item = {
-        text: error.full_message,
+        text: error_message_text(error),
         data_attributes: track_analytics_data("form-error", analytics_action, error.full_message),
       }
 
@@ -51,4 +51,34 @@ def errors
                   object.errors
                 end
   end
+
+  def error_message_text(error)
+    if custom_error_present_in_locales?(error)
+      custom_error_message(error)
+    else
+      error.full_message
+    end
+  end
+
+  def custom_error_present_in_locales?(error)
+    custom_error_message(error)
+  rescue RuntimeError
+    false
+  end
+
+  def custom_error_message(error)
+    I18n.t("activerecord.errors.models.#{model_for_locale(error)}.attributes.#{attribute_for_locale(error)}.#{error.type}")
+  end
+
+  def model_for_locale(error)
+    return parent_class unless error.is_a?(ActiveModel::NestedError)
+
+    error.attribute.to_s.split(".")[-2]
+  end
+
+  def attribute_for_locale(error)
+    return error.attribute unless error.is_a?(ActiveModel::NestedError)
+
+    error.attribute.to_s.split(".").last
+  end
 end

config/locales/en/attachments.yml

@@ -0,0 +1,8 @@
+en:
+  activerecord:
+    errors:
+      models:
+        attachment:
+          attributes:
+            title:
+              blank: Enter a title

config/locales/en/editions.yml

@@ -0,0 +1,9 @@
+en:
+  activerecord:
+    errors:
+      models:
+        edition:
+          attributes:
+            first_published_at:
+              blank: Enter the date when the document was first published
+              invalid_date: The date is not in the correct format

config/locales/en/govspeak_content.yml

@@ -0,0 +1,8 @@
+en:
+  activerecord:
+    errors:
+      models:
+        govspeak_content:
+          attributes:
+            body:
+              blank: Enter a body

features/step_definitions/previously_published_steps.rb

@@ -37,7 +37,7 @@
 end
 
 Then(/^I see a validation error for the missing publication date$/) do
-  expect(page).to have_content("First published at can't be blank")
+  expect(page).to have_content("Enter the date when the document was first published")
 end
 
 Then(/^I should not see a validation error on the previously published date$/) do

test/components/admin/error_summary_component_test.rb

@@ -109,6 +109,15 @@ class Admin::ErrorSummaryComponentTest < ViewComponent::TestCase
     assert_equal third_link.text, "Date is invalid"
     assert_equal third_link[:href], "#error_summary_test_object_date"
   end
+
+  test "Uses custom error messages when present in the locales" do
+    attachment = build(:attachment, title: nil)
+    attachment.validate
+
+    render_inline(Admin::ErrorSummaryComponent.new(object: attachment, parent_class: "attachment"))
+
+    assert_equal "Enter a title", page.all(".gem-c-error-summary__list-item")[0].find("a").text
+  end
 end
 
 class ErrorSummaryTestObject

test/functional/admin/publications_controller_test.rb

@@ -88,7 +88,7 @@ class Admin::PublicationsControllerTest < ActionController::TestCase
 
   test "should validate first_published_at field on create if previously_published is true" do
     post :create, params: { edition: controller_attributes_for(:publication).merge(previously_published: "true") }
-    assert_equal "First published at can't be blank", assigns(:edition).errors.full_messages.last
+    assert_equal "First published at Enter the date when the document was first published", assigns(:edition).errors.full_messages.last
   end
 
   view_test "edit displays publication fields and guidance" do

test/unit/app/models/edition_test.rb

@@ -783,7 +783,7 @@ class EditionTest < ActiveSupport::TestCase
   test "first_published_at required when previously_published" do
     edition = build(:edition, previously_published: true)
     assert_not edition.valid?
-    assert_equal "First published at can't be blank", edition.errors.full_messages.first
+    assert_equal "First published at Enter the date when the document was first published", edition.errors.full_messages.first
 
     edition.first_published_at = Time.zone.now
     assert edition.valid?