Properly wire stdin in client-server mode and enable "Enter to Re-run" for mill -w

[lihaoyi]

This gets rid of our custom watchAndWait logic, standardizing it with what's upstream in Ammonite and allowing Mill to use the "Enter to re-run" functionality that was introduced in Ammonite 2.5.0.

While this worked for ./mill -i out of the box, some work was necessary to get it working for Mill's client-server mode. This fixes the wiring for the socket's stdin to ensure it gets plumbed through, and works around the broken available() implementation in the UnixDomainSocketInputStream by proxying it via an InputPumper.

Tested manually:

lihaoyi mill$ ./mill -i dev.run scratch -w foo.run
[90/647] de.tobiasroeser.mill.vcs.version.VcsVersion.vcsState
[647/647] dev.run
[44/44] foo.run
false
Watching for changes to 4 paths... (Enter to re-run, Ctrl-C to exit)

<ENTER>
[44/44] foo.run
false
Watching for changes to 4 paths... (Enter to re-run, Ctrl-C to exit)

<ENTER>
[44/44] foo.run
false
Watching for changes to 4 paths... (Enter to re-run, Ctrl-C to exit)

<ENTER>
[44/44] foo.run
false
Watching for changes to 4 paths... (Enter to re-run, Ctrl-C to exit)
<Ctrl-C>
Host JVM shutdown. Forcefully destroying subprocess ...

Notably, this change also allows you to run interactive mill foo.run programs without using -i, e.g. using this modified scratch/src/Foo.scala:

package foo
object Foo{

  def main(args: Array[String]): Unit = {
    println("enter any character: ")
    val c = System.in.read().toChar
    println("c: [" + c + "]")
  }
}

lihaoyi mill$ ./mill -i dev.run scratch -w foo.run
...
[44/44] foo.run
enter any character:
g<ENTER>
c: [g]
Watching for changes to 4 paths... (Enter to re-run, Ctrl-C to exit)

[lefou]

Another great change! I love that it fixes the need to use --interactive for interactive commands.

[lefou]

LGTM!

[lihaoyi]

Notably, even the interactive Scala console works without -i now

$ ./mill -i dev.run scratch foo.console
[90/647] de.tobiasroeser.mill.vcs.version.VcsVersion.vcsState
[647/647] dev.run
[39/39] foo.console
Welcome to Scala 2.13.2 (OpenJDK 64-Bit Server VM, Java 11.0.7).
Type in expressions for evaluation. Or try :help.
Dec 15, 2021 8:59:31 PM org.jline.utils.Log logr
WARNING: Unable to create a system terminal, creating a dumb terminal (enable debug logging for more information)
1
scala> + 1
val res0: Int = 2

scala> println(123, 456)
println(123, 456)(123,456)

Not 100%, Ctrl-D doesn't work properly to exit, and I'm guessing Ammonite won't work smoothly due to the clever TTY stuff it does. Nevertheless, it's moving in the right direction to get it all working for good