extension (pos: SrcPos)
    def isZeroExtentSynthetic: Boolean = pos.span.isSynthetic && pos.span.isZeroExtent
    def isSynthetic: Boolean = pos.span.isSynthetic && pos.span.exists

  // adjust a pos at EOF if preceded by newline
  private def adjust(pos: SourcePosition): SourcePosition =
    if pos.span.isSynthetic
    && pos.span.isZeroExtent
    && pos.span.exists
    && pos.span.start == pos.source.length
    && pos.source(pos.span.start - 1) == '\n'
    then
      pos.withSpan(pos.span.shift(-1))
    else
      pos