Allow Side Effecting Statement to have Names

[ekiwi]

TODO:

• test that a circuit which has a name collision with a named statement is rejected
• test that a circuit which contains a reference to a statement is rejected
• add new feature to the firrtl spec

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?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• new feature: named print, stop and verification statements

API Impact

• extends Print, Stop and Verification nodes with a name field
• statement labels are intentionally kept optional so that old firrtl should parse and work with no problem

Backend Code Generation Impact

• this should not change the Verilog at the moment

Desired Merge Strategy

• squash

Release Notes

• print, stop, assume, assert and cover statements can now be given a name which allows them to be annotated

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) ?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you mark as Please Merge?

[davidbiancolin]

Pretty cool, i've been wanting this feature for a while. I think adding the trait might clean up the pattern matching a little bit and make it easier to add other similar nodes in the future, but i'll defer to you.

What's the chisel strategy going to be for emitting these names?

[jackkoenig]

Looks really good overall, some minor comments.

[jackkoenig]

This is super minor, but I think it'd be nice to have a newline between the @since and name just so that the types are spaced over so much

[jackkoenig]

LGTM