Simplify the logic to display the minimum password length hint

There's no real need to pass 2 variables to the view to figure that out,
we can simply display the message relying on whether or not the
`@minimum_password_length` variable is present.

CHANGELOG.md

@@ -1,6 +1,9 @@
 ### Unreleased
 
 * enhancements
+  * The hint about minimum password length required both `@validatable` and `@minimum_password_length`
+    variables on the views, it now uses only the latter. If you have generated the views
+    relying on the `@validatable` variable, replace it with `@minimum_password_length`.
   * Added an ActiveSupport load hook for `:devise_controller` (by @nakhli)
   * Location fragments are now preserved between requests (by @jbourassa)
   * Added an `after_remembered` callback for the Rememerable module (by @BM5k)

app/controllers/devise_controller.rb

@@ -156,8 +156,7 @@ MESSAGE
 
   # Sets minimum password length to show to user
   def set_minimum_password_length
-    @validatable = devise_mapping.validatable?
-    if @validatable
+    if devise_mapping.validatable?
       @minimum_password_length = resource_class.password_length.min
     end
   end

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

@@ -6,7 +6,7 @@
 
   <div class="field">
     <%= f.label :password, "New password" %><br />
-    <% if @validatable %>
+    <% if @minimum_password_length %>
     <em>(<%= @minimum_password_length %> characters minimum)</em>
     <% end %><br />
     <%= f.password_field :password, autofocus: true, autocomplete: "off" %>

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

@@ -10,7 +10,7 @@
 
   <div class="field">
     <%= f.label :password %>
-    <% if @validatable %>
+    <% if @minimum_password_length %>
     <em>(<%= @minimum_password_length %> characters minimum)</em>
     <% end %><br />
     <%= f.password_field :password, autocomplete: "off" %>

lib/generators/templates/simple_form_for/passwords/edit.html.erb

@@ -7,7 +7,7 @@
   <%= f.full_error :reset_password_token %>
 
   <div class="form-inputs">
-    <%= f.input :password, label: "New password", required: true, autofocus: true, hint: ("#{@minimum_password_length} characters minimum" if @validatable) %>
+    <%= f.input :password, label: "New password", required: true, autofocus: true, hint: ("#{@minimum_password_length} characters minimum" if @minimum_password_length) %>
     <%= f.input :password_confirmation, label: "Confirm your new password", required: true %>
   </div>
 

lib/generators/templates/simple_form_for/registrations/new.html.erb

@@ -5,7 +5,7 @@
 
   <div class="form-inputs">
     <%= f.input :email, required: true, autofocus: true %>
-    <%= f.input :password, required: true, hint: ("#{@minimum_password_length} characters minimum" if @validatable) %>
+    <%= f.input :password, required: true, hint: ("#{@minimum_password_length} characters minimum" if @minimum_password_length) %>
     <%= f.input :password_confirmation, required: true %>
   </div>