Fix a fairly serious bug whereby Vec's could incorrectly compare as equal (#204)

* chiselTests: include an example of two empty Vectors killing FIRRTL

* Aggregate: fix a bug whereby Vec[T] was using equals/hashCode of Seq

In Chisel, two vectors are NOT equal just if their contents are equal.
For example, two empty vectors should not be considered equal. This
patch makes Vec use the HasId._id for equality like other Chisel types.

Without this fix, Bundle.namedElts.seen: HashSet[Data]() will eliminate
one of the named vectors and emit bad IR.

1 files changed, 5 insertions, 1 deletions

diff --git a/chiselFrontend/src/main/scala/Chisel/Aggregate.scala b/chiselFrontend/src/main/scala/Chisel/Aggregate.scala
index 197135d7..1eef5d69 100644
--- a/chiselFrontend/src/main/scala/Chisel/Aggregate.scala
+++ b/chiselFrontend/src/main/scala/Chisel/Aggregate.scala
@@ -174,9 +174,13 @@ sealed class Vec[T <: Data] private (gen: => T, val length: Int)
 /** A trait for [[Vec]]s containing common hardware generators for collection
   * operations.
   */
-trait VecLike[T <: Data] extends collection.IndexedSeq[T] {
+trait VecLike[T <: Data] extends collection.IndexedSeq[T] with HasId {
   def apply(idx: UInt): T
 
+  // IndexedSeq has its own hashCode/equals that we must not use
+  override def hashCode: Int = super[HasId].hashCode
+  override def equals(that: Any): Boolean = super[HasId].equals(that)
+  
   @deprecated("Use Vec.apply instead", "chisel3")
   def read(idx: UInt): T