2 files changed, 67 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)
+    }
+
+}
diff --git a/src/test/scala/chiselTests/stage/phases/AddImplicitOutputAnnotationFileSpec.scala b/src/test/scala/chiselTests/stage/phases/AddImplicitOutputAnnotationFileSpec.scala
new file mode 100644
index 00000000..f5fe0440
--- /dev/null
+++ b/src/test/scala/chiselTests/stage/phases/AddImplicitOutputAnnotationFileSpec.scala
@@ -0,0 +1,42 @@
+// See LICENSE for license details.
+
+package chiselTests.stage.phases
+
+import org.scalatest.{FlatSpec, Matchers}
+
+import chisel3.experimental.RawModule
+import chisel3.stage.ChiselGeneratorAnnotation
+import chisel3.stage.phases.{AddImplicitOutputAnnotationFile, Elaborate}
+
+import firrtl.AnnotationSeq
+import firrtl.options.{OutputAnnotationFileAnnotation, Phase}
+
+class AddImplicitOutputAnnotationFileSpec extends FlatSpec with Matchers {
+
+  class Foo extends RawModule { override val desiredName = "Foo" }
+
+  class Fixture { val phase: Phase = new AddImplicitOutputAnnotationFile }
+
+  behavior of classOf[AddImplicitOutputAnnotationFile].toString
+
+  it should "not override an existing OutputAnnotationFileAnnotation" in new Fixture {
+    val annotations: AnnotationSeq = Seq(
+      ChiselGeneratorAnnotation(() => new Foo),
+      OutputAnnotationFileAnnotation("Bar") )
+
+    Seq( new Elaborate, phase )
+      .foldLeft(annotations)((a, p) => p.transform(a))
+      .collect{ case a: OutputAnnotationFileAnnotation => a.file }
+      .toSeq should be (Seq("Bar"))
+  }
+
+  it should "generate an OutputAnnotationFileAnnotation from a ChiselCircuitAnnotation" in new Fixture {
+    val annotations: AnnotationSeq = Seq( ChiselGeneratorAnnotation(() => new Foo) )
+
+    Seq( new Elaborate, phase )
+      .foldLeft(annotations)((a, p) => p.transform(a))
+      .collect{ case a: OutputAnnotationFileAnnotation => a.file }
+      .toSeq should be (Seq("Foo"))
+  }
+
+}