Remove val io

Chisel projects no longer need -Xsource:2.11 when compiling with Scala
2.12.

Autowrapping of "val io" for compatibility mode Modules is now
implemented using reflection instead of calling the virtual method.

Also move Chisel.BlackBox to new chisel3.internal.LegacyBlackBox

9 files changed, 135 insertions, 57 deletions

diff --git a/build.sbt b/build.sbt
index 267ee57f..5030c016 100644
--- a/build.sbt
+++ b/build.sbt
@@ -18,10 +18,6 @@ lazy val commonSettings = Seq (
   scalaVersion := "2.12.12",
   crossScalaVersions := Seq("2.12.12"),
   scalacOptions := Seq("-deprecation", "-feature",
-    //  We're building with Scala > 2.11, enable the compile option
-    //  switch to support our anonymous Bundle definitions:
-    //  https://github.com/scala/bug/issues/10047
-    "-Xsource:2.11"
   ),
   libraryDependencies += "org.scala-lang" % "scala-reflect" % scalaVersion.value,
   addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.1" cross CrossVersion.full),
diff --git a/build.sc b/build.sc
index 475d432d..c37b748b 100644
--- a/build.sc
+++ b/build.sc
@@ -59,8 +59,7 @@ trait CommonModule extends CrossSbtModule with PublishModule {
   override def scalacOptions = T {
     super.scalacOptions() ++ Agg(
       "-deprecation",
-      "-feature",
-      "-Xsource:2.11"
+      "-feature"
     )
   }
 
diff --git a/core/src/main/scala/chisel3/BlackBox.scala b/core/src/main/scala/chisel3/BlackBox.scala
index 1b093ee1..2aa9a243 100644
--- a/core/src/main/scala/chisel3/BlackBox.scala
+++ b/core/src/main/scala/chisel3/BlackBox.scala
@@ -134,15 +134,11 @@ package experimental {
   */
 abstract class BlackBox(val params: Map[String, Param] = Map.empty[String, Param])(implicit compileOptions: CompileOptions) extends BaseBlackBox {
 
-  @deprecated("Removed for causing issues in Scala 2.12+. You remain free to define io Bundles " +
-    "in your BlackBoxes, but you cannot rely on an io field in every BlackBox. " +
-    "For more information, see: https://github.com/freechipsproject/chisel3/pull/1550.",
-    "Chisel 3.4"
-  )
-  def io: Record
-
-  // Private accessor to reduce number of deprecation warnings
-  private[chisel3] def _io: Record = io
+  // Find a Record port named "io" for purposes of stripping the prefix
+  private[chisel3] lazy val _io: Record =
+    this.findPort("io")
+        .collect { case r: Record => r } // Must be a Record
+        .getOrElse(null) // null handling occurs in generateComponent
 
   // Allow access to bindings from the compatibility package
   protected def _compatIoPortBound() = portsContains(_io)
@@ -150,8 +146,8 @@ abstract class BlackBox(val params: Map[String, Param] = Map.empty[String, Param
   private[chisel3] override def generateComponent(): Component = {
     _compatAutoWrapPorts()  // pre-IO(...) compatibility hack
 
-    // Restrict IO to just io, clock, and reset
-    require(_io != null, "BlackBox must have io")
+  // Restrict IO to just io, clock, and reset
+    require(_io != null, "BlackBox must have a port named 'io' of type Record!")
     require(portsContains(_io), "BlackBox must have io wrapped in IO(...)")
     require(portsSize == 1, "BlackBox must only have io as IO")
 
diff --git a/core/src/main/scala/chisel3/Module.scala b/core/src/main/scala/chisel3/Module.scala
index 9a1a0ce1..d34211f1 100644
--- a/core/src/main/scala/chisel3/Module.scala
+++ b/core/src/main/scala/chisel3/Module.scala
@@ -257,6 +257,11 @@ package experimental {
     // mainly for compatibility purposes.
     protected def portsContains(elem: Data): Boolean = _ports contains elem
 
+    // This is dangerous because it can be called before the module is closed and thus there could
+    // be more ports and names have not yet been finalized.
+    // This should only to be used during the process of closing when it is safe to do so.
+    private[chisel3] def findPort(name: String): Option[Data] = _ports.find(_.seedOpt.contains(name))
+
     protected def portsSize: Int = _ports.size
 
     /** Generates the FIRRTL Component (Module or Blackbox) of this Module.
diff --git a/core/src/main/scala/chisel3/RawModule.scala b/core/src/main/scala/chisel3/RawModule.scala
index bb84c444..ac6a2d1f 100644
--- a/core/src/main/scala/chisel3/RawModule.scala
+++ b/core/src/main/scala/chisel3/RawModule.scala
@@ -3,6 +3,7 @@
 package chisel3
 
 import scala.collection.mutable.{ArrayBuffer, HashMap}
+import scala.util.Try
 import scala.collection.JavaConversions._
 import scala.language.experimental.macros
 
@@ -150,40 +151,62 @@ trait RequireSyncReset extends Module {
   override private[chisel3] def mkReset: Bool = Bool()
 }
 
-package internal {
+package object internal {
+
+  // Private reflective version of "val io" to maintain Chisel.Module semantics without having
+  // io as a virtual method. See https://github.com/freechipsproject/chisel3/pull/1550 for more
+  // information about the removal of "val io"
+  private def reflectivelyFindValIO(self: BaseModule): Record = {
+    // Java reflection is faster and works for the common case
+    def tryJavaReflect: Option[Record] = Try {
+      self.getClass.getMethod("io").invoke(self).asInstanceOf[Record]
+    }.toOption
+    // Anonymous subclasses don't work with Java reflection, so try slower, Scala reflection
+    def tryScalaReflect: Option[Record] = {
+      val ru = scala.reflect.runtime.universe
+      import ru.{Try => _, _}
+      val m = ru.runtimeMirror(self.getClass.getClassLoader)
+      val im = m.reflect(self)
+      val tpe = im.symbol.toType
+      // For some reason, in anonymous subclasses, looking up the Term by name (TermName("io"))
+      // hits an internal exception. Searching for the term seems to work though so we use that.
+      val ioTerm: Option[TermSymbol] = tpe.decls.collectFirst {
+        case d if d.name.toString == "io" && d.isTerm => d.asTerm
+      }
+      ioTerm.flatMap { term =>
+        Try {
+          im.reflectField(term).get.asInstanceOf[Record]
+        }.toOption
+      }
+    }
+
+    tryJavaReflect
+      .orElse(tryScalaReflect)
+      .map(_.autoSeed("io"))
+      .orElse {
+        // Fallback if reflection fails, user can wrap in IO(...)
+        self.findPort("io")
+          .collect { case r: Record => r }
+      }.getOrElse(throwException(
+        s"Compatibility mode Module '$this' must have a 'val io' Bundle. " +
+        "If there is such a field and you still see this error, autowrapping has failed (sorry!). " +
+        "Please wrap the Bundle declaration in IO(...)."
+      ))
+  }
 
   /** Legacy Module class that restricts IOs to just io, clock, and reset, and provides a constructor
     * for threading through explicit clock and reset.
     *
-    * While this class isn't planned to be removed anytime soon (there are benefits to restricting
-    * IO), the clock and reset constructors will be phased out. Recommendation is to wrap the module
-    * in a withClock/withReset/withClockAndReset block, or directly hook up clock or reset IO pins.
+    * This is only intended as a bridge from chisel3 to Chisel.Module, do not extend this in user
+    * code, use [[Module]]
     */
   abstract class LegacyModule(implicit moduleCompileOptions: CompileOptions) extends Module {
-    // IO for this Module. At the Scala level (pre-FIRRTL transformations),
-    // connections in and out of a Module may only go through `io` elements.
-    @deprecated("Removed for causing issues in Scala 2.12+. You remain free to define io Bundles " +
-      "in your Modules, but you cannot rely on an io field in every Module. " +
-      "For more information, see: https://github.com/freechipsproject/chisel3/pull/1550.",
-      "Chisel 3.4"
-    )
-    def io: Record
-
-    // Private accessor to reduce number of deprecation warnings
-    private[chisel3] def _io: Record = io
+
+    private lazy val _io: Record = reflectivelyFindValIO(this)
 
     // Allow access to bindings from the compatibility package
     protected def _compatIoPortBound() = portsContains(_io)
 
-    private[chisel3] override def namePorts(names: HashMap[HasId, String]): Unit = {
-      for (port <- getModulePorts) {
-        // This should already have been caught
-        if (!names.contains(port)) throwException(s"Unable to name port $port in $this")
-        val name = names(port)
-        port.setRef(ModuleIO(this, _namespace.name(name)))
-      }
-    }
-
     private[chisel3] override def generateComponent(): Component = {
       _compatAutoWrapPorts()  // pre-IO(...) compatibility hack
 
@@ -195,5 +218,33 @@ package internal {
 
       super.generateComponent()
     }
+
+    override def _compatAutoWrapPorts(): Unit = {
+      if (!_compatIoPortBound() && _io != null) {
+        _bindIoInPlace(_io)
+      }
+    }
+  }
+
+  import chisel3.experimental.Param
+
+  /** Legacy BlackBox class will reflectively autowrap val io
+    *
+    * '''Do not use this class in user code'''. Use whichever `Module` is imported by your wildcard
+    * import (preferably `import chisel3._`).
+    */
+  abstract class LegacyBlackBox(params: Map[String, Param] = Map.empty[String, Param])
+                               (implicit moduleCompileOptions: CompileOptions)
+      extends chisel3.BlackBox(params) {
+
+    override private[chisel3] lazy val _io: Record = reflectivelyFindValIO(this)
+
+    // This class auto-wraps the BlackBox with IO(...), allowing legacy code (where IO(...) wasn't
+    // required) to build.
+    override def _compatAutoWrapPorts(): Unit = {
+      if (!_compatIoPortBound()) {
+        _bindIoInPlace(_io)
+      }
+    }
   }
 }
diff --git a/src/main/scala/chisel3/compatibility.scala b/src/main/scala/chisel3/compatibility.scala
index 38ef80ba..7066384b 100644
--- a/src/main/scala/chisel3/compatibility.scala
+++ b/src/main/scala/chisel3/compatibility.scala
@@ -259,16 +259,7 @@ package object Chisel {
 
   implicit def resetToBool(reset: Reset): Bool = reset.asBool
 
-  import chisel3.experimental.Param
-  abstract class BlackBox(params: Map[String, Param] = Map.empty[String, Param]) extends chisel3.BlackBox(params) {
-    // This class auto-wraps the BlackBox with IO(...), allowing legacy code (where IO(...) wasn't
-    // required) to build.
-    override def _compatAutoWrapPorts(): Unit = {
-      if (!_compatIoPortBound()) {
-        _bindIoInPlace(io)
-      }
-    }
-  }
+  type BlackBox = chisel3.internal.LegacyBlackBox
 
   type MemBase[T <: Data] = chisel3.MemBase[T]
 
@@ -321,12 +312,6 @@ package object Chisel {
       this(None, Option(_reset))(moduleCompileOptions)
     def this(_clock: Clock, _reset: Bool)(implicit moduleCompileOptions: CompileOptions) =
       this(Option(_clock), Option(_reset))(moduleCompileOptions)
-
-    override def _compatAutoWrapPorts(): Unit = {
-      if (!_compatIoPortBound() && io != null) {
-        _bindIoInPlace(io)
-      }
-    }
   }
 
   val Module = chisel3.Module
diff --git a/src/test/scala/chiselTests/AnalogIntegrationSpec.scala b/src/test/scala/chiselTests/AnalogIntegrationSpec.scala
index 3af54d1d..7478f2eb 100644
--- a/src/test/scala/chiselTests/AnalogIntegrationSpec.scala
+++ b/src/test/scala/chiselTests/AnalogIntegrationSpec.scala
@@ -31,6 +31,10 @@ class AnalogBlackBox(index: Int) extends BlackBox(Map("index" -> index)) {
   val io = IO(new AnalogBlackBoxIO(1))
 }
 
+// This interface exists to give a common interface type for AnalogBlackBoxModule and
+// AnalogBlackBoxWrapper. This is the standard way to deal with the deprecation and removal of the
+// Module.io virtual method (same for BlackBox.io).
+// See https://github.com/freechipsproject/chisel3/pull/1550 for more information
 trait AnalogBlackBoxModuleIntf extends Module {
   def io: AnalogBlackBoxIO
 }
diff --git a/src/test/scala/chiselTests/BlackBox.scala b/src/test/scala/chiselTests/BlackBox.scala
index 8ae7d6ee..d3d52f96 100644
--- a/src/test/scala/chiselTests/BlackBox.scala
+++ b/src/test/scala/chiselTests/BlackBox.scala
@@ -15,6 +15,16 @@ class BlackBoxInverter extends BlackBox {
   })
 }
 
+// Due to the removal of "val io", this technically works
+// This style is discouraged, please use "val io"
+class BlackBoxInverterSuggestName extends BlackBox {
+  override def desiredName: String = "BlackBoxInverter"
+  val foo = IO(new Bundle() {
+    val in = Input(Bool())
+    val out = Output(Bool())
+  }).suggestName("io")
+}
+
 class BlackBoxPassthrough extends BlackBox {
   val io = IO(new Bundle() {
     val in = Input(Bool())
@@ -50,6 +60,18 @@ class BlackBoxTester extends BasicTester {
   stop()
 }
 
+class BlackBoxTesterSuggestName extends BasicTester {
+  val blackBoxPos = Module(new BlackBoxInverterSuggestName)
+  val blackBoxNeg = Module(new BlackBoxInverterSuggestName)
+
+  blackBoxPos.foo.in := 1.U
+  blackBoxNeg.foo.in := 0.U
+
+  assert(blackBoxNeg.foo.out === 1.U)
+  assert(blackBoxPos.foo.out === 0.U)
+  stop()
+}
+
 class BlackBoxFlipTester extends BasicTester {
   val blackBox = Module(new BlackBoxPassthrough2)
 
@@ -187,4 +209,10 @@ class BlackBoxSpec extends ChiselFlatSpec {
       }
     )
   }
+  "A BlackBoxed using suggestName(\"io\")" should "work (but don't do this)" in {
+    assertTesterPasses(
+      {new BlackBoxTesterSuggestName},
+      Seq("/chisel3/BlackBoxTest.v"),
+      TesterDriver.verilatorOnly)
+  }
 }
diff --git a/src/test/scala/chiselTests/CompatibilitySpec.scala b/src/test/scala/chiselTests/CompatibilitySpec.scala
index 50213d4d..6a77c821 100644
--- a/src/test/scala/chiselTests/CompatibilitySpec.scala
+++ b/src/test/scala/chiselTests/CompatibilitySpec.scala
@@ -239,6 +239,20 @@ class CompatibiltySpec extends ChiselFlatSpec with ScalaCheckDrivenPropertyCheck
     ChiselStage.elaborate { new RequireIOWrapModule() }
   }
 
+  "A Module without val io" should "throw an exception" in {
+    class ModuleWithoutValIO extends Module {
+      val foo = new Bundle {
+        val in = UInt(width = 32).asInput
+        val out = Bool().asOutput
+      }
+      foo.out := foo.in(1)
+    }
+    val e = intercept[Exception](
+      ChiselStage.elaborate { new ModuleWithoutValIO }
+    )
+    e.getMessage should include("must have a 'val io' Bundle")
+  }
+
   "A Module connecting output as source to input as sink when compiled with the Chisel compatibility package" should "not throw an exception" in {
 
     class SimpleModule extends Module {