DontCare does not support Clocks

[colinschmidt]

Type of issue: bug report | feature request

Impact: API modification

Development Phase: request

If the current behavior is a bug, please provide the steps to reproduce the problem:
Trying to connect a clock output to DontCare results in the following exception.

Caused by: chisel3.internal.ChiselException: cannot connect chisel3.core.Clock@1c9176 and chisel3.core.DontCare$@0

I would expect this to be supported. Its easy to work around by converting to/from Bool.
Is there a rationale for not support Clock or is it an oversight?

Please tell us about your environment:
chisel3 commit:

commit 10751f57c595c899b4bcb81a6b0f78319ca66eb2
Merge: dc20aa4 9fd9433
Author: Jim Lawson <ucbjrl@berkeley.edu>
Date:   Sun Mar 4 09:30:31 2018 -0800

    Merge branch '3.1.x' into 3.1.0

[azidar]

This is an oversight. Will fix.

[edwardcwang]

Would like to second this. The workaround for val deadClock = Wire(Clock()); deadClock := DontCare is also a kludge:

      val w = Wire(Bool())
      w := DontCare
      val deadClock = Wire(Clock())
      deadClock := w.asClock

[ducky64]

Potentially related to the general connect semantics discussion in #1056 ?