Add IdentityLike mix-in for TransformLike

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/src/main/scala/firrtl/options/Phase.scala b/src/main/scala/firrtl/options/Phase.scala
index ffe3788f..847a4cf2 100644
--- a/src/main/scala/firrtl/options/Phase.scala
+++ b/src/main/scala/firrtl/options/Phase.scala
@@ -79,6 +79,29 @@ trait TransformLike[A] extends LazyLogging {
 
 }
 
+/** Mix-in that makes a [[firrtl.options.TransformLike TransformLike]] guaranteed to be an identity function on some
+  * type.
+  * @tparam A the transformed type
+  */
+trait IdentityLike[A] { this: TransformLike[A] =>
+
+  /** The internal operation of this transform which, in order for this to be an identity function, must return nothing.
+    * @param a an input object
+    * @return nothing
+    */
+  protected def internalTransform(a: A): Unit = Unit
+
+  /** This method will execute `internalTransform` and then return the original input object
+    * @param a an input object
+    * @return the input object
+    */
+  final override def transform(a: A): A = {
+    internalTransform(a)
+    a
+  }
+
+}
+
 /** Mixin that defines dependencies between [[firrtl.options.TransformLike TransformLike]]s (hereafter referred to as
   * "transforms")
   *