add field ids when generating a scaffold form.

Backport of 27f103f

This is a follow up to a6d065e. When using `form_with` you must supply
field ids manually. Since the scaffold generator is using labels we
need to make sure that they are linked up properly.

railties/CHANGELOG.md

@@ -1,3 +1,11 @@
+*   Specify form field ids when generating a scaffold.
+
+    This makes sure that the labels are linked up with the fields. The
+    regression was introduced when the template was switched to
+    `form_with`.
+
+    *Yves Senn*
+
 ## Rails 5.1.0.rc1 (March 20, 2017) ##
 
 *   Add `app:update` task to engines.

railties/lib/rails/generators/erb/scaffold/templates/_form.html.erb

@@ -15,15 +15,15 @@
   <div class="field">
 <% if attribute.password_digest? -%>
     <%%= form.label :password %>
-    <%%= form.password_field :password %>
+    <%%= form.password_field :password, id: :<%= field_id(:password) %> %>
   </div>
 
   <div class="field">
     <%%= form.label :password_confirmation %>
-    <%%= form.password_field :password_confirmation %>
+    <%%= form.password_field :password_confirmation, id: :<%= field_id(:password_confirmation) %> %>
 <% else -%>
     <%%= form.label :<%= attribute.column_name %> %>
-    <%%= form.<%= attribute.field_type %> :<%= attribute.column_name %> %>
+    <%%= form.<%= attribute.field_type %> :<%= attribute.column_name %>, id: :<%= field_id(attribute.column_name) %> %>
 <% end -%>
   </div>
 

railties/lib/rails/generators/named_base.rb

@@ -149,6 +149,10 @@ def new_helper # :doc:
           "new_#{singular_table_name}_url"
         end
 
+        def field_id(attribute_name)
+          [singular_table_name, attribute_name].join('_')
+        end
+
         def singular_table_name # :doc:
           @singular_table_name ||= (pluralize_table_names? ? table_name.singularize : table_name)
         end

railties/test/generators/scaffold_generator_test.rb

@@ -437,8 +437,8 @@ def test_scaffold_generator_belongs_to
     end
 
     assert_file "app/views/accounts/_form.html.erb" do |content|
-      assert_match(/^\W{4}<%= form\.text_field :name %>/, content)
-      assert_match(/^\W{4}<%= form\.text_field :currency_id %>/, content)
+      assert_match(/^\W{4}<%= form\.text_field :name, id: :account_name %>/, content)
+      assert_match(/^\W{4}<%= form\.text_field :currency_id, id: :account_currency_id %>/, content)
     end
   end
 
@@ -461,8 +461,8 @@ def test_scaffold_generator_password_digest
     end
 
     assert_file "app/views/users/_form.html.erb" do |content|
-      assert_match(/<%= form\.password_field :password %>/, content)
-      assert_match(/<%= form\.password_field :password_confirmation %>/, content)
+      assert_match(/<%= form\.password_field :password, id: :user_password %>/, content)
+      assert_match(/<%= form\.password_field :password_confirmation, id: :user_password_confirmation %>/, content)
     end
 
     assert_file "app/views/users/index.html.erb" do |content|