2 files changed, 74 insertions, 0 deletions
diff --git a/src/main/scala/chisel3/stage/phases/AddImplicitOutputFile.scala b/src/main/scala/chisel3/stage/phases/AddImplicitOutputFile.scala
new file mode 100644
index 00000000..4a4dac72
--- /dev/null
+++ b/src/main/scala/chisel3/stage/phases/AddImplicitOutputFile.scala
@@ -0,0 +1,25 @@
+// See LICENSE for license details.
+
+package chisel3.stage.phases
+
+import firrtl.AnnotationSeq
+import firrtl.options.Phase
+
+import chisel3.stage.{ChiselCircuitAnnotation, ChiselOutputFileAnnotation}
+
+/** Add a output file for a Chisel circuit, derived from the top module in the circuit, if no
+  * [[ChiselOutputFileAnnotation]] already exists.
+  */
+class AddImplicitOutputFile extends Phase {
+
+  def transform(annotations: AnnotationSeq): AnnotationSeq =
+    annotations.collectFirst{ case _: ChiselOutputFileAnnotation  => annotations }.getOrElse{
+
+      val x: Option[AnnotationSeq] = annotations
+        .collectFirst{ case a: ChiselCircuitAnnotation =>
+          ChiselOutputFileAnnotation(a.circuit.name) +: annotations }
+
+      x.getOrElse(annotations)
+    }
+
+}
diff --git a/src/test/scala/chiselTests/stage/phases/AddImplicitOutputFileSpec.scala b/src/test/scala/chiselTests/stage/phases/AddImplicitOutputFileSpec.scala
new file mode 100644
index 00000000..411aa6ba
--- /dev/null
+++ b/src/test/scala/chiselTests/stage/phases/AddImplicitOutputFileSpec.scala
@@ -0,0 +1,49 @@
+// See LICENSE for license details.
+
+package chiselTests.stage.phases
+
+import org.scalatest.{FlatSpec, Matchers}
+
+import chisel3.experimental.RawModule
+import chisel3.stage.{ChiselGeneratorAnnotation, ChiselOutputFileAnnotation}
+import chisel3.stage.phases.{AddImplicitOutputFile, Elaborate}
+
+import firrtl.AnnotationSeq
+import firrtl.options.{Phase, StageOptions, TargetDirAnnotation}
+import firrtl.options.Viewer.view
+
+class AddImplicitOutputFileSpec extends FlatSpec with Matchers {
+
+  class Foo extends RawModule { override val desiredName = "Foo" }
+
+  class Fixture { val phase: Phase = new AddImplicitOutputFile }
+
+  behavior of classOf[AddImplicitOutputFile].toString
+
+  it should "not override an existing ChiselOutputFileAnnotation" in new Fixture {
+    val annotations: AnnotationSeq = Seq(
+      ChiselGeneratorAnnotation(() => new Foo),
+      ChiselOutputFileAnnotation("Bar") )
+
+    Seq( new Elaborate, phase )
+      .foldLeft(annotations)((a, p) => p.transform(a))
+      .collect{ case a: ChiselOutputFileAnnotation => a.file }
+      .toSeq should be (Seq("Bar"))
+  }
+
+  it should "generate a ChiselOutputFileAnnotation from a ChiselCircuitAnnotation" in new Fixture {
+    val annotations: AnnotationSeq = Seq(
+      ChiselGeneratorAnnotation(() => new Foo),
+      TargetDirAnnotation("test_run_dir") )
+
+    Seq( new Elaborate, phase )
+      .foldLeft(annotations)((a, p) => p.transform(a))
+      .collect{ case a: ChiselOutputFileAnnotation => a.file }
+      .toSeq should be (Seq("Foo"))
+  }
+
+  it should "do nothing to an empty annotation sequence" in new Fixture {
+    phase.transform(AnnotationSeq(Seq.empty)).toSeq should be (empty)
+  }
+
+}