Improve exception message for aliased bundle fields (#2304)

- Shows groups of field names that share a common id (i.e. aliased)
- Show, as much as possible, them in the order that fields appear in bundle
- Updated BundleSpec's relevant tests

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

1 files changed, 20 insertions, 1 deletions

diff --git a/core/src/main/scala/chisel3/Aggregate.scala b/core/src/main/scala/chisel3/Aggregate.scala
index 600e2d11..db354e1f 100644
--- a/core/src/main/scala/chisel3/Aggregate.scala
+++ b/core/src/main/scala/chisel3/Aggregate.scala
@@ -29,7 +29,26 @@ sealed abstract class Aggregate extends Data {
     val resolvedDirection = SpecifiedDirection.fromParent(parentDirection, specifiedDirection)
     val duplicates = getElements.groupBy(identity).collect { case (x, elts) if elts.size > 1 => x }
     if (!duplicates.isEmpty) {
-      throw new AliasedAggregateFieldException(s"Aggregate $this contains aliased fields $duplicates")
+      this match {
+        case b: Record =>
+          // show groups of names of fields with duplicate id's
+          // The sorts make the displayed order of fields deterministic and matching the order of occurrence in the Bundle.
+          // It's a bit convoluted but happens rarely and makes the error message easier to understand
+          val dupNames = duplicates.toSeq.sortBy(_._id).map { duplicate =>
+            b.elements
+              .collect { case x if x._2._id == duplicate._id => x }
+              .toSeq.sortBy(_._2._id)
+              .map(_._1).reverse
+              .mkString("(", ",", ")")
+          }.mkString(",")
+          throw new AliasedAggregateFieldException(
+            s"${b.className} contains aliased fields named ${dupNames}"
+          )
+        case _ =>
+          throw new AliasedAggregateFieldException(
+            s"Aggregate ${this.getClass} contains aliased fields $duplicates ${duplicates.mkString(",")}"
+          )
+      }
     }
     for (child <- getElements) {
       child.bind(ChildBinding(this), resolvedDirection)