bundleWithABoolProbe := 0.U.asTypeOf(bundleWithABoolProbe) results in illegal firrtl

[mwachs5]

Type of issue: Bug Report

Please provide the steps to reproduce the problem:

What is the current behavior?

Consider the following:

    class BundleWithAProbe extends Bundle {
      val tap = Probe(Bool())
    }
    class TestMod extends RawModule{
      val a = IO(Output(new BundleWithAProbe()))
      a :#= 0.U.asTypeOf(a)
    }
    ChiselStage.emitCHIRRTL(new TestMod)

This successfully emits illegal firrtl:

circuit TestMod :
  ...
  public module TestMod : @[src/test/scala/chiselTests/ProbeSpec.scala 751:11]
    output a : { tap : Probe<UInt<1>>}

    define a.tap = UInt<1>(0h0)

What is the expected behavior?

Not sure. This should at minimum not emit illegal firrtl.
If you do this without a Bundle, you get an error like:

mismatched probe/non-probe types in TestMod.a: IO[Bool] and Bool(false).
[error]       a :#= 0.U.asTypeOf(a)

And if you do it for a Probe of a Bundle you get an even better error before you even try to do the connect, which is:

"Cannot create Const of a Probe."

It should probably throw an error, making it the user's responsibility to somehow drive the probe fields to probes-of-Wires that are initialized to 0, but that could be quite annoying and a helper API to do that might also be useful.

Please tell us about your environment:

commit: cf42ac7
Date: Mon Sep 9 12:57:04 2024 -0700

Other Information

What is the use case for changing the behavior?

Chisel should generally not emit invalid firrtl