[FIRRTL] Produce Better Error Message For Incorrect Enum FIRRTL Text

[Schuyler Eldridge]

The following is currently failing:

FIRRTL version 4.0.0
circuit Foo:
  module Foo:
    wire x: UInt<8>
    node y = {|some: UInt<8>, None|}(Some, x)

The problem is that this is parsing Some, x) as the "tag" and then trying to look that. This is then an illegal tag and it errors out.

See the comment below. This is illegal IR that trips an assert in a builder.

[Schuyler Eldridge]

False alarm on this one---some and Some do not match, therefore this is malformed IR. This should produce a better error message when this does happen, though. Currently this is tripping an assertion in the builder which, in a release build, looks like it would blind dereference an optional type. 😬