Refactor the devise_error_messages! helper to render a partial (#4616)

This should make it more intuitive and easier for developers using the
project to implement their own layout for errors.

app/helpers/devise_helper.rb

@@ -1,27 +1,11 @@
 # frozen_string_literal: true
 
 module DeviseHelper
-  # A simple way to show error messages for the current devise resource. If you need
-  # to customize this method, you can either overwrite it in your application helpers or
-  # copy the views to your application.
-  #
-  # This method is intended to stay simple and it is unlikely that we are going to change
-  # it to add more behavior or options.
+  # Retain this method for backwards compatibility, deprecated in favour of modifying the
+  # devise/shared/error_messages partial
   def devise_error_messages!
     return "" if resource.errors.empty?
 
-    messages = resource.errors.full_messages.map { |msg| content_tag(:li, msg) }.join
-    sentence = I18n.t("errors.messages.not_saved",
-                      count: resource.errors.count,
-                      resource: resource.class.model_name.human.downcase)
-
-    html = <<-HTML
-    <div id="error_explanation">
-      <h2>#{sentence}</h2>
-      <ul>#{messages}</ul>
-    </div>
-    HTML
-
-    html.html_safe
+    render "devise/shared/error_messages", resource: resource
   end
 end

app/views/devise/confirmations/new.html.erb

@@ -1,7 +1,7 @@
 <h2>Resend confirmation instructions</h2>
 
 <%= form_for(resource, as: resource_name, url: confirmation_path(resource_name), html: { method: :post }) do |f| %>
-  <%= devise_error_messages! %>
+  <%= render "devise/shared/error_messages", resource: resource %>
 
   <div class="field">
     <%= f.label :email %><br />

app/views/devise/passwords/edit.html.erb

@@ -1,7 +1,7 @@
 <h2>Change your password</h2>
 
 <%= form_for(resource, as: resource_name, url: password_path(resource_name), html: { method: :put }) do |f| %>
-  <%= devise_error_messages! %>
+  <%= render "devise/shared/error_messages", resource: resource %>
   <%= f.hidden_field :reset_password_token %>
 
   <div class="field">

app/views/devise/passwords/new.html.erb

@@ -1,7 +1,7 @@
 <h2>Forgot your password?</h2>
 
 <%= form_for(resource, as: resource_name, url: password_path(resource_name), html: { method: :post }) do |f| %>
-  <%= devise_error_messages! %>
+  <%= render "devise/shared/error_messages", resource: resource %>
 
   <div class="field">
     <%= f.label :email %><br />

app/views/devise/registrations/edit.html.erb

@@ -1,7 +1,7 @@
 <h2>Edit <%= resource_name.to_s.humanize %></h2>
 
 <%= form_for(resource, as: resource_name, url: registration_path(resource_name), html: { method: :put }) do |f| %>
-  <%= devise_error_messages! %>
+  <%= render "devise/shared/error_messages", resource: resource %>
 
   <div class="field">
     <%= f.label :email %><br />

app/views/devise/registrations/new.html.erb

@@ -1,7 +1,7 @@
 <h2>Sign up</h2>
 
 <%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
-  <%= devise_error_messages! %>
+  <%= render "devise/shared/error_messages", resource: resource %>
 
   <div class="field">
     <%= f.label :email %><br />

app/views/devise/shared/_error_messages.html.erb

@@ -0,0 +1,15 @@
+<% if resource.errors.any? %>
+  <div id="error_explanation">
+    <h2>
+      <%= I18n.t("errors.messages.not_saved",
+                 count: resource.errors.count,
+                 resource: resource.class.model_name.human.downcase)
+       %>
+    </h2>
+    <ul>
+      <% resource.errors.full_messages.each do |message| %>
+        <li><%= message %>
+      <% end %>
+    </ul>
+  </div>
+<% end %>

app/views/devise/unlocks/new.html.erb

@@ -1,7 +1,7 @@
 <h2>Resend unlock instructions</h2>
 
 <%= form_for(resource, as: resource_name, url: unlock_path(resource_name), html: { method: :post }) do |f| %>
-  <%= devise_error_messages! %>
+  <%= render "devise/shared/error_messages", resource: resource %>
 
   <div class="field">
     <%= f.label :email %><br />