Arel: make Or nodes "Nary" like And

Fix: rails#51386

This significantly reduce the depth of the tree for large `OR`
conditions. I was initially a bit on the fence about that fix,
but given that `And` is already implemented this way, I see no
reasons not to do the same.

Amusingly, the reported repro script now makes SQLite fail:

```ruby
SQLite3::SQLException: Expression tree is too large (maximum depth 1000)
```

Author: byroot

activerecord/lib/active_record/relation/predicate_builder.rb

@@ -142,7 +142,7 @@ def grouping_queries(queries)
           queries.first
         else
           queries.map! { |query| query.reduce(&:and) }
-          queries = queries.reduce { |result, query| Arel::Nodes::Or.new(result, query) }
+          queries = queries.reduce { |result, query| Arel::Nodes::Or.new([result, query]) }
           Arel::Nodes::Grouping.new(queries)
         end
       end

activerecord/lib/active_record/relation/query_methods.rb

@@ -1098,7 +1098,7 @@ def or!(other) # :nodoc:
         raise ArgumentError, "Relation passed to #or must be structurally compatible. Incompatible values: #{incompatible_values}"
       end
 
-      self.where_clause = self.where_clause.or(other.where_clause)
+      self.where_clause = where_clause.or(other.where_clause)
       self.having_clause = having_clause.or(other.having_clause)
       self.references_values |= other.references_values
 

activerecord/lib/active_record/relation/where_clause.rb

@@ -47,7 +47,11 @@ def or(other)
           right = right.ast
           right = right.expr if right.is_a?(Arel::Nodes::Grouping)
 
-          or_clause = Arel::Nodes::Or.new(left, right)
+          or_clause = if left.is_a?(Arel::Nodes::Or)
+            Arel::Nodes::Or.new(left.children + [right])
+          else
+            Arel::Nodes::Or.new([left, right])
+          end
 
           common.predicates << Arel::Nodes::Grouping.new(or_clause)
           common

activerecord/lib/arel/nodes.rb

@@ -41,8 +41,8 @@
 require "arel/nodes/regexp"
 require "arel/nodes/cte"
 
-# nary
-require "arel/nodes/and"
+# nary (And and Or)
+require "arel/nodes/nary"
 
 # function
 # FIXME: Function + Alias can be rewritten as a Function and Alias node.

activerecord/lib/arel/nodes/binary.rb

@@ -111,12 +111,6 @@ def invert
       end
     end
 
-    class Or < Binary
-      def fetch_attribute(&block)
-        left.fetch_attribute(&block) && right.fetch_attribute(&block)
-      end
-    end
-
     %w{
       Assignment
       Join

activerecord/lib/arel/nodes/and.rb renamed to activerecord/lib/arel/nodes/nary.rb

@@ -2,7 +2,7 @@
 
 module Arel # :nodoc: all
   module Nodes
-    class And < Arel::Nodes::NodeExpression
+    class Nary < Arel::Nodes::NodeExpression
       attr_reader :children
 
       def initialize(children)
@@ -23,7 +23,7 @@ def fetch_attribute(&block)
       end
 
       def hash
-        children.hash
+        [self.class, children].hash
       end
 
       def eql?(other)
@@ -32,5 +32,8 @@ def eql?(other)
       end
       alias :== :eql?
     end
+
+    And = Class.new(Nary)
+    Or = Class.new(Nary)
   end
 end

activerecord/lib/arel/nodes/node.rb

@@ -127,7 +127,7 @@ def not
       # Factory method to create a Nodes::Grouping node that has an Nodes::Or
       # node as a child.
       def or(right)
-        Nodes::Grouping.new Nodes::Or.new(self, right)
+        Nodes::Grouping.new Nodes::Or.new([self, right])
       end
 
       ###

activerecord/lib/arel/predications.rb

@@ -232,7 +232,7 @@ def quoted_array(others)
       def grouping_any(method_id, others, *extras)
         nodes = others.map { |expr| send(method_id, expr, *extras) }
         Nodes::Grouping.new nodes.inject { |memo, node|
-          Nodes::Or.new(memo, node)
+          Nodes::Or.new([memo, node])
         }
       end
 

activerecord/lib/arel/visitors/dot.rb

@@ -191,6 +191,7 @@ def visit__children(o)
           end
         end
         alias :visit_Arel_Nodes_And :visit__children
+        alias :visit_Arel_Nodes_Or :visit__children
         alias :visit_Arel_Nodes_With :visit__children
 
         def visit_String(o)

activerecord/lib/arel/visitors/to_sql.rb

@@ -622,18 +622,7 @@ def visit_Arel_Nodes_And(o, collector)
         end
 
         def visit_Arel_Nodes_Or(o, collector)
-          stack = [o.right, o.left]
-
-          while o = stack.pop
-            if o.is_a?(Arel::Nodes::Or)
-              stack.push o.right, o.left
-            else
-              visit o, collector
-              collector << " OR " unless stack.empty?
-            end
-          end
-
-          collector
+          inject_join o.children, collector, " OR "
         end
 
         def visit_Arel_Nodes_Assignment(o, collector)