Name the targets of identity views (backport #4222)

core/src/main/scala/chisel3/internal/Builder.scala

@@ -17,7 +17,7 @@ import _root_.firrtl.AnnotationSeq
 import _root_.firrtl.renamemap.MutableRenameMap
 import _root_.firrtl.util.BackendCompilationUtilities._
 import _root_.firrtl.{ir => fir}
-import chisel3.experimental.dataview.{reify, reifySingleTarget}
+import chisel3.experimental.dataview.{reify, reifyIdentityView, reifySingleTarget}
 import chisel3.internal.Builder.Prefix
 import logger.{LazyLogging, LoggerOption}
 
@@ -874,6 +874,12 @@ private[chisel3] object Builder extends LazyLogging {
         case Clone(m: experimental.hierarchy.ModuleClone[_]) => namer(m.getPorts, prefix)
         case _ =>
       }
+    case (d: Data) =>
+      // Views are often returned in lieu of the target, so name the target (as appropriate).
+      // If a view but not identity, return the view and name it since it shows up in .toString and error messages.
+      // TODO recurse on targets of non-identity views, perhaps with additional prefix from the view.
+      val reified = reifyIdentityView(d).fold(d)(_._1)
+      namer(reified, prefix)
     case (id: HasId) => namer(id, prefix)
     case Some(elt) => nameRecursively(prefix, elt, namer)
     case (iter: Iterable[_]) if iter.hasDefiniteSize =>

src/test/scala/chiselTests/Vec.scala

@@ -319,9 +319,9 @@ class VecSpec extends ChiselPropSpec with Utils {
 
     })
     chirrtl should include("output io : { foo : UInt<1>, bar : UInt<1>[0]}")
-    chirrtl should include("wire _zero_WIRE : { foo : UInt<1>, bar : UInt<1>[0]}")
-    chirrtl should include("connect _zero_WIRE.foo, UInt<1>(0h0)")
-    chirrtl should include("connect io, _zero_WIRE")
+    chirrtl should include("wire zero : { foo : UInt<1>, bar : UInt<1>[0]}")
+    chirrtl should include("connect zero.foo, UInt<1>(0h0)")
+    chirrtl should include("connect io, zero")
     chirrtl should include("wire w : UInt<1>[0]")
     chirrtl should include("connect w, m.io.bar")
   }

src/test/scala/chiselTests/naming/NamePluginSpec.scala

@@ -437,4 +437,22 @@ class NamePluginSpec extends ChiselFlatSpec with Utils {
       Select.wires(top).map(_.instanceName) should be(List())
     }
   }
+
+  "identity views" should "forward names to their targets" in {
+    import chisel3.experimental.dataview._
+    class Test extends Module {
+      val x = {
+        val _w = Wire(UInt(3.W))
+        _w.viewAs[UInt]
+      }
+      val y = Wire(UInt(3.W)).readOnly // readOnly is implemented with views
+
+      val z = Wire(UInt(3.W))
+      val zz = z.viewAs[UInt] // But don't accidentally override names
+    }
+
+    aspectTest(() => new Test) { top: Test =>
+      Select.wires(top).map(_.instanceName) should be(List("x", "y", "z"))
+    }
+  }
 }