Deprecate limit strings with commas

Some backends allow `LIMIT 1,2` as a shorthand for `LIMIT 1 OFFSET 2`.
Supporting this in Active Record massively complicates using bind
parameters for limit and offset, and it's trivially easy to build an
invalid SQL query by also calling `offset` on the same `Relation`.

This is a niche syntax that is only supported by a few adapters, and can
be trivially worked around by calling offset explicitly.

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index dbecb842b5..f7115c7a91 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -677,6 +677,12 @@ module ActiveRecord
     end
 
     def limit!(value) # :nodoc:
+      if ::String === value && value.include?(",")
+        ActiveSupport::Deprecation.warn(<<-WARNING)
+          Passing a string to limit in the form "1,2" is deprecated and will be
+          removed in Rails 5.1. Please call `offset` explicitly instead.
+        WARNING
+      end
       self.limit_value = value
       self
     end