Raise an error if scope or enum is about to add a conflicting method to the class

[chancancode]

See #13389 for details. I left out case 4, because that does not particularly concerns me, and I don't think checking klass.new.respond_to?(...) is a good idea.

cc @senny @dhh

[senny]

@chancancode did you consider 813c8c0 ? What can be the sign of a mistake is a feature in other situations.

As an illustration:

module Publishable
  extend ActiveSupport::Concern

  included do
    enum status: [:proposed, :written, :published]
  end

  def published!
    super
    "do publish work..."
  end
end

[schneems]

@senny we could do some metaprogramming to avoid that scenario using singleton_method_added like this:

class ActiveRecord; end
class ActiveRecord::Base
  class << self
    def singleton_method_added(method_name)
      puts "We could check '#{method_name}' as it is added to #{self}"
      super
    end
  end
end

class Barz < ActiveRecord::Base
  def self.any_method_you_want
  end
end

# => "We could check 'any_method_you_want' as it is added to Barz"

Though this only works if the singleton_method_added is already inherited or included, if you put the include at the bottom of the class, it wouldn't check anything.

[chancancode]

@senny, good catch, will update to make this order independent

[chancancode]

@senny updated!

[schneems]

Tangent: 

It would have been easier if there was an accessor method/object.

Model.enum.shipped?

Instead of the method going straight on the class:

Model.shipped?

—
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On Tue, Dec 24, 2013 at 6:22 AM, Godfrey Chan notifications@github.com
wrote:

@senny updated!

Reply to this email directly or view it on GitHub:
#13450 (comment)

[chancancode]

@schneems check out the discussion in #13389 :)

[rafaelfranca]

Seems good to me

[rafaelfranca]

Will this handle private methods too?

[chancancode]

Fixed via in chancancode@f350402, thanks 😁

[chancancode]

Update: some open points...

1. Base.method_defined?("#{value}?") is no good (doesn't check for private methods, etc). Should use the same logic as dangerous_attribute?. Resolution: I'm going to do a small refactor to make those methods available here and reuse them.
2. if respond_to?(value) doesn't check for private class methods etc, but by doing so it'll raise on many not-too-dangerous cases (e.g. you cannot have a scope called open because it conflicts with Kernel.open which was mixed into Class. Resolution: use a mixed blacklist approach.

[chancancode]

@rafaelfranca @senny Sorry for the hold up, I re-implemented this just now. The 'dangerous' logic is basically the same as attribute method (defined on Base but not on Base.superclass) for both instance and class method. The only exception is that enum instance methods conflicts with stuff added from another enum from within the same class.

This catches the most "dangerous" scenarios (conflict with AR internals) but still allows the programmer to do some potentially dangerous stuff such as re-defining a scope/enum in a subclass or override an existing user-defined class method with a scope.

I also thought about extracting some of these into Active Support, but the logic we use here is actually quite specific to AR, so I don't know how useful that would be. If you still think that's helpful I can give it a shot.

[chancancode]

The extraction would look roughly like this:

class Module
  def method_defined_within?(name, sup = Module)
    if method_defined?(name) || private_method_defined?(name)
      if sup.method_defined?(name) || sup.private_method_defined?(name)
        instance_method(name).owner != sup.instance_method(name).owner
      else
        true
      end
    else
      false
    end
  end

  def class_method_defined_within?(name, sup = Module)
    if respond_to?(name, true)
      if sup.respond_to?(name, true)
        method(name).owner != sup.method(name).owner
      else
        true
      end
    else
      false
    end
  end

  private
    def safe_define_method(name, base = self, sup = Module, &block)
      unless base.method_defined_within?(name, sup)
        define_method(name, &block)
      end
    end

    def safe_define_method!(name, base = self, sup = Module, &block)
      safe_define_method(name, base, sup, &block) ||
        raise ArgumentError, "Attempted to redefine the method #{name} " \
          "when it is already defined by #{base.name}."
    end

    def safe_define_class_method(name, base = self, sup = Module, &block)
      unless base.class_method_defined_within?(name, sup)
        base.singleton_class.send(:define_method, name, &block)
      end
    end

    def safe_define_class_method!(name, base = self, sup = Module, &block)
      safe_define_class_method(name, base, sup, block) ||
        raise ArgumentError, "Attempted to redefine the class method #{name} " \
          "when it is already defined by #{base.name}."
    end
end

class Class
  def method_defined_within?(name, sup = self.superclass)
    super(name, sup)
  end

  def class_method_defined_within?(name, sup = self.superclass)
    super(name, sup)
  end

  private
    def safe_define_method(name, base = self, sup = base.superclass, &block)
      super(name, base, sup, &block)
    end

    def safe_define_method!(name, base = self, sup = base.superclass, &block)
      super(name, base, sup, &block)
    end

    def safe_define_class_method(name, base = self, sup = base.superclass, &block)
      super(name, base, sup, &block)
    end

    def safe_define_class_method!(name, base = self, sup = base.superclass, &block)
      super(name, base, sup, &block)
    end
end

[seuros]

With this change, tables that use uuid as id and redefine :first and :last are broken now.

[rafaelfranca]

Redefine how?

[seuros]

Like this
scope :first, -> { order('created_at').first }
scope :last, -> { order('created_at DESC').first }

[rafaelfranca]

why would you do this?

But anyway, you still can have the same behavior.

def self.first
  order('created_at').first
end

def self.last
  order('created_at DESC').first
end

[carlosantoniodasilva]

In general you should not use scopes to return AR objects, scopes should return other relations. In any case you can still use class methods for that, as @rafaelfranca just pointed out.

[seuros]

Thanks you @rafaelfranca