1 files changed, 25 insertions, 0 deletions
diff --git a/src/main/scala/chisel3/stage/phases/AddImplicitOutputAnnotationFile.scala b/src/main/scala/chisel3/stage/phases/AddImplicitOutputAnnotationFile.scala
new file mode 100644
index 00000000..de251ab6
--- /dev/null
+++ b/src/main/scala/chisel3/stage/phases/AddImplicitOutputAnnotationFile.scala
@@ -0,0 +1,25 @@
+// See LICENSE for license details.
+
+package chisel3.stage.phases
+
+import chisel3.stage.ChiselCircuitAnnotation
+import firrtl.AnnotationSeq
+import firrtl.options.{OutputAnnotationFileAnnotation, Phase}
+
+/** Adds an [[firrtl.options.OutputAnnotationFileAnnotation]] if one does not exist. This replicates old behavior where
+  * an output annotation file was always written.
+  */
+class AddImplicitOutputAnnotationFile extends Phase {
+
+  def transform(annotations: AnnotationSeq): AnnotationSeq = annotations
+    .collectFirst{ case _: OutputAnnotationFileAnnotation => annotations }
+    .getOrElse{
+
+      val x: Option[AnnotationSeq] = annotations
+        .collectFirst{ case a: ChiselCircuitAnnotation =>
+          OutputAnnotationFileAnnotation(a.circuit.name) +: annotations }
+
+      x.getOrElse(annotations)
+    }
+
+}