Add opt-in AutoCloneType for Records (backport #2781) (#2785)

* Add opt-in AutoCloneType for Records (#2781)

There is a new trait, chisel3.experimental.AutoCloneType that is mixed
in to Bundle and can optionally be mixed in to user-defined Records. The
compiler plugin prints a deprecation warning on any user-defined
implementation of cloneType, telling the user to mix in AutoCloneType
before upgrading to 3.6.

(cherry picked from commit a234fd48ac8f5942c38fef5797292014e407b586)

# Conflicts:
#	core/src/main/scala/chisel3/Aggregate.scala
#	plugin/src/main/scala/chisel3/internal/plugin/BundleComponent.scala

* Resolve backport conflicts

* Do not make MixedVec extend AutoCloneType

It is a binary incompatible change that can wait for 3.6.

* Waive MiMa false positives

Co-authored-by: Jack Koenig <koenig@sifive.com>

1 files changed, 22 insertions, 10 deletions

diff --git a/core/src/main/scala/chisel3/Aggregate.scala b/core/src/main/scala/chisel3/Aggregate.scala
index 042e78b1..aacf0b1c 100644
--- a/core/src/main/scala/chisel3/Aggregate.scala
+++ b/core/src/main/scala/chisel3/Aggregate.scala
@@ -1158,6 +1158,16 @@ abstract class Record(private[chisel3] implicit val compileOptions: CompileOptio
     * Results in "`\$className(elt0.name -> elt0.value, ...)`"
     */
   def toPrintable: Printable = toPrintableHelper(elements.toList)
+
+  /** Implementation of cloneType that is [optionally for Record] overridden by the compiler plugin
+    *
+    * @note This should _never_ be overridden or called in user-code
+    */
+  protected def _cloneTypeImpl: Record = {
+    throwException(
+      s"Internal Error! This should have been implemented by the chisel3-plugin. Please file an issue against chisel3"
+    )
+  }
 }
 
 /**
@@ -1182,6 +1192,15 @@ package experimental {
   class BundleLiteralException(message: String) extends ChiselException(message)
   class VecLiteralException(message: String) extends ChiselException(message)
 
+  /** Indicates that the compiler plugin should generate [[cloneType]] for this type
+    *
+    * All user-defined [[Record]]s should mix this trait in as it will be required for upgrading to Chisel 3.6.
+    */
+  trait AutoCloneType { self: Record =>
+
+    override def cloneType: this.type = _cloneTypeImpl.asInstanceOf[this.type]
+
+  }
 }
 
 /** Base class for data types defined as a bundle of other data types.
@@ -1217,7 +1236,7 @@ package experimental {
   *   }
   * }}}
   */
-abstract class Bundle(implicit compileOptions: CompileOptions) extends Record {
+abstract class Bundle(implicit compileOptions: CompileOptions) extends Record with experimental.AutoCloneType {
   assert(
     _usingPlugin,
     "The Chisel compiler plugin is now required for compiling Chisel code. " +
@@ -1385,15 +1404,8 @@ abstract class Bundle(implicit compileOptions: CompileOptions) extends Record {
     clone
   }
 
-  /** Implementation of cloneType using runtime reflection. This should _never_ be overridden or called in user-code
-    *
-    * @note This is overridden by the compiler plugin (this implementation is never called)
-    */
-  protected def _cloneTypeImpl: Bundle = {
-    throwException(
-      s"Internal Error! This should have been implemented by the chisel3-plugin. Please file an issue against chisel3"
-    )
-  }
+  // This is overriden for binary compatibility reasons in 3.5
+  override protected def _cloneTypeImpl: Bundle = super._cloneTypeImpl.asInstanceOf[Bundle]
 
   /** Default "pretty-print" implementation
     * Analogous to printing a Map