diff options
| -rw-r--r-- | activesupport/lib/active_support/whiny_nil.rb | 43 | ||||
| -rw-r--r-- | activesupport/test/whiny_nil_test.rb | 40 |
2 files changed, 83 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/whiny_nil.rb b/activesupport/lib/active_support/whiny_nil.rb new file mode 100644 index 0000000000..4a83cd585e --- /dev/null +++ b/activesupport/lib/active_support/whiny_nil.rb @@ -0,0 +1,43 @@ +# Extensions to nil which allow for more helpful error messages for +# people who are new to rails. +# +# The aim is to ensure that when users pass nil to methods where that isn't +# appropriate, instead of NoMethodError and the name of some method used +# by the framework users will see a message explaining what type of object +# was expected. + + +class NilClass + WHINERS = [ ActiveRecord::Base, Array ] + + @@method_class_map = Hash.new + + WHINERS.each do |klass| + methods = klass.public_instance_methods - public_instance_methods + methods.each do |method| + @@method_class_map[method.to_sym] = klass + end + end + + private + def method_missing(method, *args, &block) + if @@method_class_map.include?(method) + raise_nil_warning_for @@method_class_map[method] + else + super + end + end + + def raise_nil_warning_for(klass) + raise NoMethodError, NIL_WARNING_MESSAGE % klass + end + + NIL_WARNING_MESSAGE = <<-end_message unless const_defined?(:NIL_WARNING_MESSAGE) +WARNING: You have a nil object when you probably didn't expect it! Odds are you +want an instance of %s instead. + +Look in the callstack to see where you're working with an object that could be nil. +Investigate your methods and make sure the object is what you expect! + end_message +end + diff --git a/activesupport/test/whiny_nil_test.rb b/activesupport/test/whiny_nil_test.rb new file mode 100644 index 0000000000..ffa15ceeaa --- /dev/null +++ b/activesupport/test/whiny_nil_test.rb @@ -0,0 +1,40 @@ +require 'test/unit' + + +## mock to enable testing without activerecord +module ActiveRecord + class Base + def save! + end + end +end + +require 'active_support/whiny_nil' + + + +class WhinyNilTest < Test::Unit::TestCase + def test_unchanged + begin + nil.method_thats_not_in_whiners + rescue NoMethodError => nme + assert_match(/nil:NilClass/, nme.message) + end + end + + def test_active_record + begin + nil.save! + rescue NoMethodError => nme + assert(!(nme.message =~ /nil:NilClass/)) + end + end + + def test_array + begin + nil.each + rescue NoMethodError => nme + assert(!(nme.message =~ /nil:NilClass/)) + end + end +end
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