[plugin] Disable BundleComponent by default, add option to enable

build.sbt

@@ -179,6 +179,8 @@ lazy val chisel = (project in file(".")).
     mimaPreviousArtifacts := Set(),
     libraryDependencies += defaultVersions("treadle") % "test",
     scalacOptions in Test ++= Seq("-language:reflectiveCalls"),
+    // Only used in Test for 3.4.x, used in Compile in 3.5
+    scalacOptions in Test += "-P:chiselplugin:useBundlePlugin",
     scalacOptions in Compile in doc ++= Seq(
       "-diagrams",
       "-groups",

plugin/src/main/scala-2.12/chisel3/internal/plugin/BundleComponent.scala

@@ -10,7 +10,9 @@ import scala.tools.nsc.symtab.Flags
 import scala.tools.nsc.transform.TypingTransformers
 
 // TODO This component could also implement val elements in Bundles
-private[plugin] class BundleComponent(val global: Global) extends PluginComponent with TypingTransformers {
+private[plugin] class BundleComponent(val global: Global, arguments: ChiselPluginArguments)
+    extends PluginComponent
+    with TypingTransformers {
   import global._
 
   val phaseName: String = "chiselbundlephase"
@@ -23,8 +25,17 @@ private[plugin] class BundleComponent(val global: Global) extends PluginComponen
       // This plugin doesn't work on Scala 2.11 nor Scala 3. Rather than complicate the sbt build flow,
       // instead we just check the version and if its an early Scala version, the plugin does nothing
       val scalaVersion = scala.util.Properties.versionNumberString.split('.')
-      if (scalaVersion(0).toInt == 2 && scalaVersion(1).toInt >= 12) {
+      val scalaVersionOk = scalaVersion(0).toInt == 2 && scalaVersion(1).toInt >= 12
+      if (scalaVersionOk && arguments.useBundlePlugin) {
         unit.body = new MyTypingTransformer(unit).transform(unit.body)
+      } else {
+        val reason = if (!scalaVersionOk) {
+          s"invalid Scala version '${scala.util.Properties.versionNumberString}'"
+        } else {
+          s"not enabled via '${arguments.useBundlePluginFullOpt}'"
+        }
+        // Enable this with scalacOption '-Ylog:chiselbundlephase'
+        global.log(s"Skipping BundleComponent on account of $reason.")
       }
     }
   }

plugin/src/main/scala-2.12/chisel3/internal/plugin/ChiselPlugin.scala

@@ -6,13 +6,32 @@ import scala.tools.nsc
 import nsc.Global
 import nsc.plugins.{Plugin, PluginComponent}
 
+private[plugin] case class ChiselPluginArguments(var useBundlePlugin: Boolean = false) {
+  def useBundlePluginOpt = "useBundlePlugin"
+  def useBundlePluginFullOpt = s"-P:chiselplugin:$useBundlePluginOpt"
+}
+
 // The plugin to be run by the Scala compiler during compilation of Chisel code
 class ChiselPlugin(val global: Global) extends Plugin {
   val name = "chiselplugin"
   val description = "Plugin for Chisel 3 Hardware Description Language"
+  private val arguments = ChiselPluginArguments()
   val components: List[PluginComponent] = List[PluginComponent](
     new ChiselComponent(global),
-    new BundleComponent(global)
+    new BundleComponent(global, arguments)
   )
+
+  override def init(options: List[String], error: String => Unit): Boolean = {
+    for (option <- options) {
+      if (option == arguments.useBundlePluginOpt) {
+        arguments.useBundlePlugin = true
+      } else {
+        error(s"Option not understood: '$option'")
+      }
+    }
+    true
+  }
+
+
 }
 

src/test/scala/chiselTests/AutoClonetypeSpec.scala

@@ -4,6 +4,7 @@ package chiselTests
 
 import chisel3._
 import chisel3.testers.TestUtils
+import chisel3.util.QueueIO
 
 class BundleWithIntArg(val i: Int) extends Bundle {
   val out = UInt(i.W)
@@ -65,6 +66,11 @@ class NestedAnonymousBundle extends Bundle {
 // Not necessarily good style (and not necessarily recommended), but allowed to preserve compatibility.
 class BundleWithArgumentField(val x: Data, val y: Data) extends Bundle
 
+// Needs to be top-level so that reflective autoclonetype works
+class InheritingBundle extends QueueIO(UInt(8.W), 8) {
+  val error = Output(Bool())
+}
+
 // TODO all `.suggestNames` are due to https://github.com/chipsalliance/chisel3/issues/1802
 class AutoClonetypeSpec extends ChiselFlatSpec with Utils {
   val usingPlugin: Boolean = TestUtils.usingPlugin
@@ -253,10 +259,21 @@ class AutoClonetypeSpec extends ChiselFlatSpec with Utils {
     elaborate(new MyModule(3))
   }
 
+  behavior of "Compiler Plugin Autoclonetype"
+
+  // Necessary test for 3.4.x, but we will break this (for non-plugin users) in 3.5
+  it should "NOT break code that extends chisel3.util Bundles (whether they use the plugin or not)" in {
+    class MyModule extends MultiIOModule {
+      val io = IO(new InheritingBundle)
+      io.deq <> io.enq
+      io.count := 0.U
+      io.error := true.B
+    }
+    elaborate(new MyModule)
+  }
+
   // New tests from the plugin
   if (usingPlugin) {
-    behavior of "Compiler Plugin Autoclonetype"
-
     it should "support Bundles with non-val parameters" in {
       class MyBundle(i: Int) extends Bundle {
         val foo = UInt(i.W)