2 files changed, 23 insertions, 5 deletions
diff --git a/chiselFrontend/src/main/scala/chisel3/core/Aggregate.scala b/chiselFrontend/src/main/scala/chisel3/core/Aggregate.scala
index 82c6097f..e6ecff91 100644
--- a/chiselFrontend/src/main/scala/chisel3/core/Aggregate.scala
+++ b/chiselFrontend/src/main/scala/chisel3/core/Aggregate.scala
@@ -48,8 +48,21 @@ object Vec {
     // with apply(Seq) after type erasure. Workarounds by either introducing a
     // DummyImplicit or additional type parameter will break some code.
     require(!elts.isEmpty)
-    val width = elts.map(_.width).reduce(_ max _)
-    val vec = Wire(new Vec(elts.head.cloneTypeWidth(width), elts.length))
+    def gen = elts.head match {
+      case e: Element =>
+        // Vec[Element] must have homogeneous types, but may differ in width
+        for (elt <- elts.tail)
+          require(e.getClass == elt.getClass,
+              s"can't create Vec of heterogeneous types ${e.getClass} and ${elt.getClass}")
+        val maxWidth = elts.map(_.width).reduce(_ max _)
+        elts.head.cloneTypeWidth(maxWidth)
+      case a: Aggregate =>
+        // Vec[Aggregate] must be homogeneous in type and width
+        for (elt <- elts.tail)
+          require(Mux.typesCompatible(a, elt), s"can't create Vec of heterogeneous types ${a.getClass} and ${elt.getClass}")
+        elts.head.cloneType
+    }
+    val vec = Wire(new Vec(gen, elts.length))
     for ((v, e) <- vec zip elts)
       v := e
     vec
diff --git a/chiselFrontend/src/main/scala/chisel3/core/Bits.scala b/chiselFrontend/src/main/scala/chisel3/core/Bits.scala
index 015b9dfb..44beab66 100644
--- a/chiselFrontend/src/main/scala/chisel3/core/Bits.scala
+++ b/chiselFrontend/src/main/scala/chisel3/core/Bits.scala
@@ -737,10 +737,15 @@ object Mux {
     pushOp(DefPrim(sourceInfo, d, MultiplexOp, cond.ref, con.ref, alt.ref))
   }
 
+  private[core] def typesCompatible[T <: Data](x: T, y: T): Boolean = {
+    val sameTypes = x.getClass == y.getClass
+    val sameElements = x.flatten zip y.flatten forall { case (a, b) => a.getClass == b.getClass && a.width == b.width }
+    val sameNumElements = x.flatten.size == y.flatten.size
+    sameTypes && sameElements && sameNumElements
+  }
+
   private def doAggregateMux[T <: Data](cond: Bool, con: T, alt: T)(implicit sourceInfo: SourceInfo): T = {
-    require(con.getClass == alt.getClass, s"can't Mux between ${con.getClass} and ${alt.getClass}")
-    for ((c, a) <- con.flatten zip alt.flatten)
-      require(c.width == a.width, "can't Mux between aggregates of different width")
+    require(typesCompatible(con, alt), s"can't Mux between heterogeneous types ${con.getClass} and ${alt.getClass}")
     doMux(cond, con, alt)
   }
 }