Tweak Bundle._elementsImpl (#2390) (#2392)

* Change type of Bundle._elementsImpl to Iterable

It was previously SeqMap (ListMap on Scala 2.12). This change gives us
more freedom to optimize the implementation without breaking binary
compatibility. It is scala.collection.Iterable because it is perfectly
fine to return mutable collections (like Arrays) since the only use is
to Iterate on them.

* Disallow users implementing Bundle._elementsImpl

Currently, it would result in a runtime linkage error. This turns it
into a compile-time error.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
(cherry picked from commit 1b05a14ad6d5784f3b91ab510dc1095423c23ea8)

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

1 files changed, 11 insertions, 8 deletions

diff --git a/plugin/src/main/scala/chisel3/internal/plugin/BundleComponent.scala b/plugin/src/main/scala/chisel3/internal/plugin/BundleComponent.scala
index e92bbb23..d768175d 100644
--- a/plugin/src/main/scala/chisel3/internal/plugin/BundleComponent.scala
+++ b/plugin/src/main/scala/chisel3/internal/plugin/BundleComponent.scala
@@ -41,12 +41,12 @@ private[plugin] class BundleComponent(val global: Global, arguments: ChiselPlugi
 
     def inferType(t: Tree): Type = localTyper.typed(t, nsc.Mode.TYPEmode).tpe
 
-    val bundleTpe:     Type = inferType(tq"chisel3.Bundle")
-    val dataTpe:       Type = inferType(tq"chisel3.Data")
-    val ignoreSeqTpe:  Type = inferType(tq"chisel3.IgnoreSeqInBundle")
-    val seqOfDataTpe:  Type = inferType(tq"scala.collection.Seq[chisel3.Data]")
-    val someOfDataTpe: Type = inferType(tq"scala.Option[chisel3.Data]")
-    val seqMapTpe:     Type = inferType(tq"scala.collection.immutable.SeqMap[String,Any]")
+    val bundleTpe:      Type = inferType(tq"chisel3.Bundle")
+    val dataTpe:        Type = inferType(tq"chisel3.Data")
+    val ignoreSeqTpe:   Type = inferType(tq"chisel3.IgnoreSeqInBundle")
+    val seqOfDataTpe:   Type = inferType(tq"scala.collection.Seq[chisel3.Data]")
+    val someOfDataTpe:  Type = inferType(tq"scala.Option[chisel3.Data]")
+    val itStringAnyTpe: Type = inferType(tq"scala.collection.Iterable[(String,Any)]")
 
     // Not cached because it should only be run once per class (thus once per Type)
     def isBundle(sym: Symbol): Boolean = { sym.tpe <:< bundleTpe }
@@ -95,6 +95,9 @@ private[plugin] class BundleComponent(val global: Global, arguments: ChiselPlugi
         case d: DefDef if isNullaryMethodNamed("_cloneTypeImpl", d) =>
           val msg = "Users cannot override _cloneTypeImpl. Let the compiler plugin generate it."
           global.globalError(d.pos, msg)
+        case d: DefDef if isNullaryMethodNamed("_elementsImpl", d) =>
+          val msg = "Users cannot override _elementsImpl. Let the compiler plugin generate it."
+          global.globalError(d.pos, msg)
         case d: DefDef if isNullaryMethodNamed("_usingPlugin", d) =>
           val msg = "Users cannot override _usingPlugin, it is for the compiler plugin's use only."
           global.globalError(d.pos, msg)
@@ -220,10 +223,10 @@ private[plugin] class BundleComponent(val global: Global, arguments: ChiselPlugi
           val elementsImplSym =
             bundle.symbol.newMethod(TermName("_elementsImpl"), bundle.symbol.pos.focus, Flag.OVERRIDE | Flag.PROTECTED)
           elementsImplSym.resetFlag(Flags.METHOD)
-          elementsImplSym.setInfo(NullaryMethodType(seqMapTpe))
+          elementsImplSym.setInfo(NullaryMethodType(itStringAnyTpe))
 
           val elementsImpl = localTyper.typed(
-            DefDef(elementsImplSym, q"scala.collection.immutable.SeqMap.apply[String, Any](..$elementArgs)")
+            DefDef(elementsImplSym, q"scala.collection.immutable.Vector.apply[(String, Any)](..$elementArgs)")
           )
 
           Some(elementsImpl)