Add basic Chisel2 compatibility sanity checks.

[ucbjrl]

No description provided.

[ducky64]

The first part looks like a direct transformation of the Chisel compatibility package. Is it useful, and what kind of bugs is it expected to catch?
Potentially related: https://docs.google.com/document/d/13k8AsgYdF-2TJx9QIHHvPiuV3JMbsrMLkWmmjdYBLVg/edit

The Chisel2 RISC tester makes sense, but I don't think it's well targeted. What Chisel2 compatibility features in particular is it trying to test? Can we directly test those? I imagine individual tests that exercise the different connection semantics would be more useful, especially because a failure gives you a specific cause instead of "my omnibus processor test is on fire".

[ucbjrl]

Good point on the compatibility package transform. I'll pull it.

[ucbjrl]

The Chisel2 RISC tester is a "sanity" check, which is the issue this test is trying to address.

Testing individual connection semantics is a good idea. I'll add some.

[jackkoenig]

@ucbjrl Can you check out why this is failing?

[ucbjrl]

It's because of src/main/scala/chisel3/compatibility.scala:273

  require(!nodeType.widthKnown, "Bit width may no longer be specified for enums")

Introduced by Simplify Enum API (#385) edb19a0, and CompatibilitySpec.scala:126

val add_op :: imm_op :: Nil = Enum(Bits(width = 8), 2)

Should we update the test or the new (incompatible) requirement?

[ducky64]

I'd argue for changing the test. It makes no sense to specify a width in an enum since you can't control the values, and I don't think it was used outside chisel tests.

[ucbjrl]

ping

[chick]

lgtm

[jackkoenig]

I don't know what this line does, but it's awesome