Allow BoringUtils.bore to work on probes (#3908) (#3910)

Extends BorginUtils.bore (and related) to work where the source is a
probe.  Currently, if a user tries to do this, they will get an error
about being unable to probe a probe because the old code would
unconditionally wrap whatever the source was in `Probe`/`RWProbe`.  Change
this to not wrap if the source is already a probe.

Signed-off-by: Schuyler Eldridge <[email protected]>
(cherry picked from commit 67f51b8)

Co-authored-by: Schuyler Eldridge <[email protected]>

src/main/scala/chisel3/util/experimental/BoringUtils.scala

@@ -224,9 +224,14 @@ object BoringUtils {
     else if (DataMirror.hasOuterFlip(source)) Flipped(chiselTypeOf(source))
     else chiselTypeOf(source)
     def purePortType = createProbe match {
-      case Some(pi) if pi.writable => RWProbe(purePortTypeBase)
-      case Some(pi)                => Probe(purePortTypeBase)
-      case None                    => purePortTypeBase
+      case Some(pi) =>
+        // If the source is already a probe, don't double wrap it in a probe.
+        purePortTypeBase.probeInfo match {
+          case Some(_)             => purePortTypeBase
+          case None if pi.writable => RWProbe(purePortTypeBase)
+          case None                => Probe(purePortTypeBase)
+        }
+      case None => purePortTypeBase
     }
     def isPort(d: Data): Boolean = d.topBindingOpt match {
       case Some(PortBinding(_)) => true

src/test/scala/chiselTests/BoringUtilsTapSpec.scala

@@ -495,4 +495,21 @@ class BoringUtilsTapSpec extends ChiselFlatSpec with ChiselRunners with Utils wi
     val verilog = circt.stage.ChiselStage.emitSystemVerilog(new Foo)
   }
 
+  it should "allow tapping a probe" in {
+    class Bar extends RawModule {
+      val a = IO(probe.Probe(Bool()))
+    }
+    class Foo extends RawModule {
+      val b = IO(probe.Probe(Bool()))
+      val bar = Module(new Bar)
+      probe.define(b, BoringUtils.tap(bar.a))
+    }
+
+    val chirrtl = circt.stage.ChiselStage.emitCHIRRTL(new Foo)
+
+    matchesAndOmits(chirrtl)(
+      "define b = bar.a"
+    )()
+  }
+
 }