InterfaceExpr introduces scope box for exprs in signatures

[dckc]

When I try to monte eval scopeBug.mt:

exports (main)

def Ast :DeepFrozen := astBuilder.getAstGuard()

interface TypeVariable :DeepFrozen {
    to setInstance(other: (def AstType :DeepFrozen := Any[Ast, TypeVariable]))
}


def main(_) as DeepFrozen:
    traceln(AstType)
    traceln(TypeVariable)

I get:

TRACE: time 1552600639.209721 vat pa
 ~ "Loader args: [\"run\", \"scopeBug\", \"eval\", \"scopeBug.mt\"]"
TRACE: time 1552600639.209760 vat pa
 ~ "Loading scopeBug"
Name AstType has no scope
RPython traceback:
  File "implement.c", line 58, in entryPoint
  File "implement.c", line 4137, in runTyphon
  File "implement.c", line 5954, in runUntilDone
  File "typhon_vats.c", line 449, in Vat_takeSomeTurns
  File "typhon_vats.c", line 1544, in Vat_takeTurn
  File "typhon_objects.c", line 5690, in Object_callAtom
  File "implement.c", line 32882, in WhenReactor_recvNamed
  File "typhon_objects.c", line 42098, in WhenReactor_run
  File "typhon_objects.c", line 5690, in Object_callAtom
  File "typhon_nano.c", line 9903, in InterpObject_runMethod
  File "implement_1.c", line 42501, in Pass_visitExpr_1
  File "typhon_nano.c", line 19173, in Evaluator_visitSeqExpr
  File "typhon_nano.c", line 14749, in Evaluator_visitDefExpr
  File "typhon_nano.c", line 14150, in Evaluator_visitCallExpr
  File "typhon_objects.c", line 5690, in Object_callAtom
  File "implement_4.c", line 62726, in AstEval0_recvNamed
  File "typhon_scopes.c", line 12898, in AstEval0_evalToPair
  File "typhon_nano_1.c", line 37235, in evalToPair
  File "typhon_nano.c", line 233, in evalMonte
  File "typhon_nano.c", line 5488, in mainPipeline
  File "implement_2.c", line 46128, in Pass_visitExpr_14
  File "typhon_nano_1.c", line 11433, in ScopeFrame_computeFrameTable
Fatal RPython error: CompilerFailed

[washort]

The name verifier incorrectly treats InterfaceExpr as not introducing a scope box, and by our syntax principles it's quite surprising that it does. So AstType being undefined in traceln(AstType) is not caught statically, and thus produces this error at runtime.