case WILL_CLOSE:
        case CLOSING:
        case CLOSED:
          throw new IllegalStateException("Cannot call finishToFuture() twice");

        case OPEN:
          throw new AssertionError();
      }
    }
    return future;
  }

  /**

        ManyClassesInSupertypeListImpl(
            firDiagnostic as KtPsiDiagnostic,
            token,
        )
    }
    add(FirErrors.SUPERTYPE_APPEARS_TWICE) { firDiagnostic ->
        SupertypeAppearsTwiceImpl(
            firDiagnostic as KtPsiDiagnostic,
            token,
        )
    }
    add(FirErrors.CLASS_IN_SUPERTYPE_FOR_ENUM) { firDiagnostic ->

<a href="#Function_declarations">function</a>,
<a href="#Labeled_statements">label</a>, or
<a href="#Import_declarations">package</a>.
Every identifier in a program must be declared.
No identifier may be declared twice in the same block, and
no identifier may be declared in both the file and package block.
</p>

<p>
The <a href="#Blank_identifier">blank identifier</a> may be used like any other identifier