Migrations: move version-finding responsibility

`ActiveRecord::Migration` needn't know about migration version
compatibility lookup. Delegate it to the Compatibility module.

Signed-off-by: Jeremy Daer <jeremydaer@gmail.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/migration/compatibility.rb b/activerecord/lib/active_record/migration/compatibility.rb
index a20d7e0820..69bd9ff1cf 100644
--- a/activerecord/lib/active_record/migration/compatibility.rb
+++ b/activerecord/lib/active_record/migration/compatibility.rb
@@ -1,6 +1,16 @@
 module ActiveRecord
   class Migration
     module Compatibility # :nodoc: all
+      def self.find(version)
+        version = version.to_s
+        name = "V#{version.tr('.', '_')}"
+        unless const_defined?(name)
+          versions = constants.grep(/\AV[0-9_]+\z/).map { |s| s.to_s.delete('V').tr('_', '.').inspect }
+          raise ArgumentError, "Unknown migration version #{version.inspect}; expected one of #{versions.sort.join(', ')}"
+        end
+        const_get(name)
+      end
+
       V5_0 = Current
 
       module FourTwoShared