FIRRTL version support

[zyedidia]

Now that FIRRTL supports version specifiers (chipsalliance/firrtl-spec#30), the parser here should accept versions and the serializer should emit a version. The current version of FIRRTL is 1.1.0. This FIRRTL compiler will throw an error if used to compile FIRRTL with a version greater than 1.1.x (e.g., >= 1.2.0). The serializer currently emits FIRRTL version 1.1.0.

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you update the FIRRTL spec to include every new feature/behavior?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you state the API impact?
• Did you specify the code generation impact?
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• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• new feature/API

API Impact

The serializer will now emit a FIRRTL version number, and the parser will accept one and throw an error if it is above 1.1.0.

Backend Code Generation Impact

No impact.

Desired Merge Strategy

Squash.

Release Notes

The serializer will now emit a FIRRTL version number, and the parser will accept one and throw an error if it is above 1.1.0.

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels?
• Did you mark the proper milestone (1.2.x, 1.3.0, 1.4.0) ?
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• Did you mark as Please Merge?

[CLAassistant]

All committers have signed the CLA.

[seldridge]

This would probably be better described as a product and if this was defined globally so this can be used in parser/Listener.scala:

case class Version(major: Int, minor: Int, patch: Int) extends scala.math.Ordered[Version] {
  override def serialize: String = ???
  override def compare(that: Version): Bool = ???
}

This would simplify some things later, e.g., exiting if the input version is too new.

Also, should this be defined in IR.scala?

[jackkoenig]

I'm okay with it being in IR.scala but I'd like to avoid modifying anything in IR.scala if we can avoid it (to avoid backwards compatibility concerns with existing transforms).

[zyedidia]

I've made a Version class in Serializer.scala that is similar to this. Instead of having a compare method it has an incompatible method, since I think compare should check the patch version, but we want to be able to accept larger versions as long as only the patch is larger. Let me know if this needs more changes.

[jackkoenig]

I think this is reasonable. If we need to do more work here later we can but this looks good enough to me.

[jackkoenig]

LGTM!

[ekiwi]