add forward_stdin test option

[t-bltg]

Fix #3185.

Should be backported to 1.8.

[fredrikekre]

Wouldn't it be better to setup your own stdin that you control instead?

[t-bltg]

Wouldn't it be better to setup your own stdin that you control instead?

How can I do that ? AFAIK there is now way to recover the parent stdin fd from the child process when the parent runs asynchronously (wait=false). We need the terminal stdin to parse terminal replies to escape sequences - being written to the parent stdin.

import Base: TTY

main() = begin
  script = """
  import Base: TTY

  println("== child ==")
  @show stdin stdin isa TTY

  # recover parent stdin fd ?
  """
  @show stdin stdin isa TTY Base._fd(stdin)
  run(pipeline(`$(Base.julia_cmd()) -e $script`, stdout=stdout, stderr=stderr), wait=false) |> wait  # mimic src/Operations.jl
  return
end

main()

output

stdin = TTY(RawFD(10) open, 0 bytes waiting)
stdin isa TTY = true
Base._fd(stdin) = RawFD(10)
== child ==
stdin = IOStream(<fd 9>)
stdin isa TTY = false