Add missing hash, eql?, == to various node classes

Some of the nodes classes are missing either one or many of the common comparison methods #hash, #eql? and #==.

This makes comparision and working with the ast sometimes painful, as equality or operations likes array differences (which uses a hash behind the scene) produces unexpected results.

A test has been added that ensures that every descendants of Node:
* have all 3 methods
* that all 3 methods were defined from the same class
* that the class defining all 3 is also a descendant of Node, to avoid the default ones that rely on identity only

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/arel/nodes/function.rb b/lib/arel/nodes/function.rb
index 28a394e9f3..b2b89ee9ff 100644
--- a/lib/arel/nodes/function.rb
+++ b/lib/arel/nodes/function.rb
@@ -29,6 +29,8 @@ module Arel
           self.alias == other.alias &&
           self.distinct == other.distinct
       end
+      alias :== :eql?
+
     end
 
     %w{