add helper function to convert chirrtl to firrtl. (#1854)

* add convert(chirrtl: cir.Circuit): fir.Circuit to convert chirrtl to firrtl.

* add scaladoc.

* add test.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

2 files changed, 27 insertions, 0 deletions

diff --git a/src/main/scala/chisel3/stage/ChiselStage.scala b/src/main/scala/chisel3/stage/ChiselStage.scala
index 1bcf5124..989b3a17 100644
--- a/src/main/scala/chisel3/stage/ChiselStage.scala
+++ b/src/main/scala/chisel3/stage/ChiselStage.scala
@@ -172,6 +172,26 @@ object ChiselStage {
       .get
   }
 
+  /** Return a [[firrtl.ir.Circuit]] for a [[chisel3.internal.firrtl.Circuit]](aka chirrtl)
+    * @param chirrtl [[chisel3.internal.firrtl.Circuit]] which need to be converted to [[firrtl.ir.Circuit]]
+    */
+  def convert(chirrtl: cir.Circuit): fir.Circuit = {
+    val phase = new ChiselPhase {
+      override val targets = Seq(
+        Dependency[chisel3.stage.phases.AddImplicitOutputFile],
+        Dependency[chisel3.stage.phases.AddImplicitOutputAnnotationFile],
+        Dependency[chisel3.stage.phases.MaybeAspectPhase],
+        Dependency[chisel3.stage.phases.Convert] )
+    }
+
+    phase
+      .transform(Seq(ChiselCircuitAnnotation(chirrtl)))
+      .collectFirst {
+        case FirrtlCircuitAnnotation(a) => a
+      }
+      .get
+  }
+
   /** Return a CHIRRTL string for a Chisel module
     * @param gen a call-by-name Chisel module
     */
diff --git a/src/test/scala/chiselTests/stage/ChiselStageSpec.scala b/src/test/scala/chiselTests/stage/ChiselStageSpec.scala
index 167e414b..7b6a2d39 100644
--- a/src/test/scala/chiselTests/stage/ChiselStageSpec.scala
+++ b/src/test/scala/chiselTests/stage/ChiselStageSpec.scala
@@ -88,6 +88,13 @@ class ChiselStageSpec extends AnyFlatSpec with Matchers with Utils {
     catchWrites { ChiselStage.convert(new Foo) } shouldBe a[Right[_, _]]
   }
 
+  ignore should "generate a FIRRTL circuit from a CHIRRTL circuit" in {
+    info("no files were written")
+    catchWrites {
+      ChiselStage.convert(ChiselStage.elaborate(new Foo))
+    } shouldBe a[Right[_, _]]
+  }
+
   behavior of "ChiselStage$.emitChirrtl"
 
   ignore should "generate a CHIRRTL string from a Chisel module" in {