Remove unused `DepthFirst` visitor

We only use `ToSQL` visitors in the our codebase, do not use
`DepthFirst` and `Dot` visitors.

The `DepthFirst` visitor (which was introduced at c86c37e5f) is used to
traverse an Arel (partial) ast with depth first.

Is there any worth to keep that undocumented feature with much code and
test cases.

This removes that unused `DepthFirst` code and test cases.

1 files changed, 0 insertions, 8 deletions

diff --git a/activerecord/lib/arel/nodes/node.rb b/activerecord/lib/arel/nodes/node.rb
index 8086102bde..0416ff58de 100644
--- a/activerecord/lib/arel/nodes/node.rb
+++ b/activerecord/lib/arel/nodes/node.rb
@@ -6,7 +6,6 @@ module Arel # :nodoc: all
     # Abstract base class for all AST nodes
     class Node
       include Arel::FactoryMethods
-      include Enumerable
 
       ###
       # Factory method to create a Nodes::Not node that has the recipient of
@@ -38,13 +37,6 @@ module Arel # :nodoc: all
         collector = engine.connection.visitor.accept self, collector
         collector.value
       end
-
-      # Iterate through AST, nodes will be yielded depth-first
-      def each(&block)
-        return enum_for(:each) unless block_given?
-
-        ::Arel::Visitors::DepthFirst.new(block).accept self
-      end
     end
   end
 end