entc: add codegen support for mixin

Summary: Pull Request resolved: https://github.com/facebookincubator/ent/pull/43

Reviewed By: alexsn

Differential Revision: D17600868

fbshipit-source-id: 39a242a541fa2a2dd2db1c9919fecf192ff098bf

entc/integration/migrate/entv1/user/user.go

@@ -42,6 +42,7 @@ var Columns = []string{
 
 var (
 	fields = schema.User{}.Fields()
+
 	// descName is the schema descriptor for name field.
 	descName = fields[1].Descriptor()
 	// NameValidator is a validator for the "name" field. It is called by the builders before save.

entc/integration/migrate/entv2/user/user.go

@@ -48,10 +48,12 @@ var Columns = []string{
 
 var (
 	fields = schema.User{}.Fields()
+
 	// descBuffer is the schema descriptor for buffer field.
 	descBuffer = fields[3].Descriptor()
 	// DefaultBuffer holds the default value on creation for the buffer field.
 	DefaultBuffer = descBuffer.Default.([]byte)
+
 	// descTitle is the schema descriptor for title field.
 	descTitle = fields[4].Descriptor()
 	// DefaultTitle holds the default value on creation for the title field.