Deprecate passing offset to find_nth

All uses of the `offset` are passing `offset_index`. Better to push
down the `offset` consideration into `find_nth`.

This also works toward enabling `find_nth_with_limit` to take
advantage of the `loaded?` state of the relation.

activerecord/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Deprecate sending the `offset` argument to `find_nth`. Please use the
+    `offset` method on relation instead.
+
+    *Ben Woosley*
+
 ## Rails 5.0.0.beta1 (December 18, 2015) ##
 
 *   Order the result of `find(ids)` to match the passed array, if the relation

activerecord/lib/active_record/relation/finder_methods.rb

@@ -119,7 +119,7 @@ def first(limit = nil)
       if limit
         find_nth_with_limit(offset_index, limit)
       else
-        find_nth(0, offset_index)
+        find_nth 0
       end
     end
 
@@ -169,7 +169,7 @@ def last!
     #   Person.offset(3).second # returns the second object from OFFSET 3 (which is OFFSET 4)
     #   Person.where(["user_name = :u", { u: user_name }]).second
     def second
-      find_nth(1, offset_index)
+      find_nth 1
     end
 
     # Same as #second but raises ActiveRecord::RecordNotFound if no record
@@ -185,7 +185,7 @@ def second!
     #   Person.offset(3).third # returns the third object from OFFSET 3 (which is OFFSET 5)
     #   Person.where(["user_name = :u", { u: user_name }]).third
     def third
-      find_nth(2, offset_index)
+      find_nth 2
     end
 
     # Same as #third but raises ActiveRecord::RecordNotFound if no record
@@ -201,7 +201,7 @@ def third!
     #   Person.offset(3).fourth # returns the fourth object from OFFSET 3 (which is OFFSET 6)
     #   Person.where(["user_name = :u", { u: user_name }]).fourth
     def fourth
-      find_nth(3, offset_index)
+      find_nth 3
     end
 
     # Same as #fourth but raises ActiveRecord::RecordNotFound if no record
@@ -217,7 +217,7 @@ def fourth!
     #   Person.offset(3).fifth # returns the fifth object from OFFSET 3 (which is OFFSET 7)
     #   Person.where(["user_name = :u", { u: user_name }]).fifth
     def fifth
-      find_nth(4, offset_index)
+      find_nth 4
     end
 
     # Same as #fifth but raises ActiveRecord::RecordNotFound if no record
@@ -233,7 +233,7 @@ def fifth!
     #   Person.offset(3).forty_two # returns the forty-second object from OFFSET 3 (which is OFFSET 44)
     #   Person.where(["user_name = :u", { u: user_name }]).forty_two
     def forty_two
-      find_nth(41, offset_index)
+      find_nth 41
     end
 
     # Same as #forty_two but raises ActiveRecord::RecordNotFound if no record
@@ -488,17 +488,25 @@ def find_take
       end
     end
 
-    def find_nth(index, offset)
+    def find_nth(index, offset = nil)
       if loaded?
         @records[index]
       else
+        if offset
+          ActiveSupport::Deprecation.warn(<<-MSG.squish)
+            Passing an offset argument to find_nth is deprecated,
+            please use Relation#offset instead.
+          MSG
+        else
+          offset = offset_index
+        end
         offset += index
         @offsets[offset] ||= find_nth_with_limit(offset, 1).first
       end
     end
 
     def find_nth!(index)
-      find_nth(index, offset_index) or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
+      find_nth(index) or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
     end
 
     def find_nth_with_limit(offset, limit)