1 files changed, 91 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/migration/compatibility.rb b/activerecord/lib/active_record/migration/compatibility.rb
new file mode 100644
index 0000000000..1b94573870
--- /dev/null
+++ b/activerecord/lib/active_record/migration/compatibility.rb
@@ -0,0 +1,91 @@
+module ActiveRecord
+  class Migration
+    module Compatibility # :nodoc: all
+      V5_0 = Current
+
+      module FourTwoShared
+        module TableDefinition
+          def timestamps(*, **options)
+            options[:null] = true if options[:null].nil?
+            super
+          end
+        end
+
+        def create_table(table_name, options = {})
+          if block_given?
+            super(table_name, options) do |t|
+              class << t
+                prepend TableDefinition
+              end
+              yield t
+            end
+          else
+            super
+          end
+        end
+
+        def add_timestamps(*, **options)
+          options[:null] = true if options[:null].nil?
+          super
+        end
+
+        def index_exists?(table_name, column_name, options = {})
+          column_names = Array(column_name).map(&:to_s)
+          options[:name] =
+            if options.key?(:name).present?
+              options[:name].to_s
+            else
+              index_name(table_name, column: column_names)
+            end
+          super
+        end
+
+        def remove_index(table_name, options = {})
+          options = { column: options } unless options.is_a?(Hash)
+          options[:name] = index_name_for_remove(table_name, options)
+          super(table_name, options)
+        end
+
+        private
+
+        def index_name_for_remove(table_name, options = {})
+          index_name = index_name(table_name, options)
+
+          unless index_name_exists?(table_name, index_name, true)
+            if options.is_a?(Hash) && options.has_key?(:name)
+              options_without_column = options.dup
+              options_without_column.delete :column
+              index_name_without_column = index_name(table_name, options_without_column)
+
+              return index_name_without_column if index_name_exists?(table_name, index_name_without_column, false)
+            end
+
+            raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' does not exist"
+          end
+
+          index_name
+        end
+      end
+
+      class V4_2 < V5_0
+        # 4.2 is defined as a module because it needs to be shared with
+        # Legacy. When the time comes, V5_0 should be defined straight
+        # in its class.
+        include FourTwoShared
+      end
+
+      module Legacy
+        include FourTwoShared
+
+        def run(*)
+          ActiveSupport::Deprecation.warn \
+            "Directly inheriting from ActiveRecord::Migration is deprecated. " \
+            "Please specify the Rails release the migration was written for:\n" \
+            "\n" \
+            "  class #{self.class.name} < ActiveRecord::Migration[4.2]"
+          super
+        end
+      end
+    end
+  end
+end