Abandon TOP support.

Initially, `TOP` was introduced to support `limit` for MSSQL database.
Unlike PostgreSQL/MySQL/SQLite, MSSQL does not have native `LIMIT`/`OFFSET` support.
The commit adding `TOP` is 1a246f71616cf246a75ef6cbdb56032e43d4e643.

However, it figured out that `TOP` implementation was weak and it's not sufficient
to also support `OFFSET`, then `TOP` was substituted with
`ROW_NUMBER()` subquery in be48ed3071fd6524d0145c4ad3faeb4aafe3eda3.
This is a well known trick in MSSQL -
https://stackoverflow.com/questions/2135418/equivalent-of-limit-and-offset-for-sql-server.

So now we don't need this `visit_Arel_Nodes_Top` at all.
It does nothing useful but also adds an extra space after `SELECT` when `LIMIT` is being
used for **any** database.

2 files changed, 2 insertions, 5 deletions

diff --git a/activerecord/lib/arel/nodes/select_core.rb b/activerecord/lib/arel/nodes/select_core.rb
index 2defe61974..73461ff683 100644
--- a/activerecord/lib/arel/nodes/select_core.rb
+++ b/activerecord/lib/arel/nodes/select_core.rb
@@ -3,13 +3,12 @@
 module Arel # :nodoc: all
   module Nodes
     class SelectCore < Arel::Nodes::Node
-      attr_accessor :top, :projections, :wheres, :groups, :windows
+      attr_accessor :projections, :wheres, :groups, :windows
       attr_accessor :havings, :source, :set_quantifier
 
       def initialize
         super()
         @source         = JoinSource.new nil
-        @top            = nil
 
         # https://ronsavage.github.io/SQL/sql-92.bnf.html#set%20quantifier
         @set_quantifier = nil
@@ -43,7 +42,7 @@ module Arel # :nodoc: all
 
       def hash
         [
-          @source, @top, @set_quantifier, @projections,
+          @source, @set_quantifier, @projections,
           @wheres, @groups, @havings, @windows
         ].hash
       end
@@ -51,7 +50,6 @@ module Arel # :nodoc: all
       def eql?(other)
         self.class == other.class &&
           self.source == other.source &&
-          self.top == other.top &&
           self.set_quantifier == other.set_quantifier &&
           self.projections == other.projections &&
           self.wheres == other.wheres &&
diff --git a/activerecord/lib/arel/nodes/unary.rb b/activerecord/lib/arel/nodes/unary.rb
index a3c0045897..00639304e4 100644
--- a/activerecord/lib/arel/nodes/unary.rb
+++ b/activerecord/lib/arel/nodes/unary.rb
@@ -37,7 +37,6 @@ module Arel # :nodoc: all
       On
       Ordering
       RollUp
-      Top
     }.each do |name|
       const_set(name, Class.new(Unary))
     end