Add IdentityTransform

This adds an identity transform that applies an identity function to some
CircuitState, i.e., it just returns the original CircuitState. This is
useful for transform generators that may, for edge cases, generate an
empty transform sequence. Other classes (e.g., Compiler) have explicit or
implicit requirements that a transform sequence is non-empty.

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

1 files changed, 17 insertions, 0 deletions

diff --git a/src/main/scala/firrtl/transforms/IdentityTransform.scala b/src/main/scala/firrtl/transforms/IdentityTransform.scala
new file mode 100644
index 00000000..a39ca4b7
--- /dev/null
+++ b/src/main/scala/firrtl/transforms/IdentityTransform.scala
@@ -0,0 +1,17 @@
+// See LICENSE for license details.
+
+package firrtl.transforms
+
+import firrtl.{CircuitForm, CircuitState, Transform}
+
+/** Transform that applies an identity function. This returns an unmodified [[CircuitState]].
+  * @param form the input and output [[CircuitForm]]
+  */
+class IdentityTransform(form: CircuitForm) extends Transform {
+
+  final override def inputForm: CircuitForm = form
+  final override def outputForm: CircuitForm = form
+
+  final def execute(state: CircuitState): CircuitState = state
+
+}