1 files changed, 50 insertions, 0 deletions
diff --git a/railties/lib/rails/generators/app_name.rb b/railties/lib/rails/generators/app_name.rb
new file mode 100644
index 0000000000..5bb735c4e8
--- /dev/null
+++ b/railties/lib/rails/generators/app_name.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+module Rails
+  module Generators
+    module AppName # :nodoc:
+      RESERVED_NAMES = %w(application destroy plugin runner test)
+
+      private
+        def app_name
+          @app_name ||= original_app_name.tr('\\', "").tr("-. ", "_")
+        end
+
+        def original_app_name
+          @original_app_name ||= defined_app_const_base? ? defined_app_name : File.basename(destination_root)
+        end
+
+        def defined_app_name
+          defined_app_const_base.underscore
+        end
+
+        def defined_app_const_base
+          Rails.respond_to?(:application) && defined?(Rails::Application) &&
+            Rails.application.is_a?(Rails::Application) && Rails.application.class.name.chomp("::Application")
+        end
+
+        alias :defined_app_const_base? :defined_app_const_base
+
+        def app_const_base
+          @app_const_base ||= defined_app_const_base || app_name.gsub(/\W/, "_").squeeze("_").camelize
+        end
+        alias :camelized :app_const_base
+
+        def app_const
+          @app_const ||= "#{app_const_base}::Application"
+        end
+
+        def valid_const?
+          if /^\d/.match?(app_const)
+            raise Error, "Invalid application name #{original_app_name}. Please give a name which does not start with numbers."
+          elsif RESERVED_NAMES.include?(original_app_name)
+            raise Error, "Invalid application name #{original_app_name}. Please give a " \
+                         "name which does not match one of the reserved rails " \
+                         "words: #{RESERVED_NAMES.join(", ")}"
+          elsif Object.const_defined?(app_const_base)
+            raise Error, "Invalid application name #{original_app_name}, constant #{app_const_base} is already in use. Please choose another application name."
+          end
+        end
+    end
+  end
+end