Warn users if Simple Form is not configured in the application

lib/simple_form.rb

@@ -36,6 +36,12 @@ to
 See https://github.com/plataformatec/simple_form/pull/997 for more information.
   WARN
 
+  @@configured = false
+
+  def self.configured? #:nodoc:
+    @@configured
+  end
+
   ## CONFIGURATION OPTIONS
 
   # Method used to tidy up errors.
@@ -235,6 +241,7 @@ See https://github.com/plataformatec/simple_form/pull/997 for more information.
   # Default way to setup SimpleForm. Run rails generate simple_form:install
   # to create a fresh initializer with all configuration values.
   def self.setup
+    @@configured = true
     yield self
   end
 end

lib/simple_form/railtie.rb

@@ -3,5 +3,12 @@ require 'rails/railtie'
 module SimpleForm
   class Railtie < Rails::Railtie
     config.eager_load_namespaces << SimpleForm
+
+    config.after_initialize do
+      unless SimpleForm.configured?
+        warn '[Simple Form] Simple Form is not configured in the application and will use the default values.' +
+          ' Use `rails generate simple_form:install` to generate the Simple Form configuration.'
+      end
+    end
   end
 end

test/simple_form_test.rb

@@ -6,4 +6,12 @@ class SimpleFormTest < ActiveSupport::TestCase
       assert_equal SimpleForm, config
     end
   end
+
+  test 'setup block configure Simple Form' do
+    SimpleForm.setup do |config|
+      assert_equal SimpleForm, config
+    end
+
+    assert_equal true, SimpleForm.configured?
+  end
 end