Provide a prompt hook in bin/ysh

[andychu]

There will be some way to reuse a PS1 string, but we want something better for Oil

https://oilshell.zulipchat.com/#narrow/stream/121540-oil-discuss/topic/Setting.20the.20prompt.20in.20Oil

[andychu]

some variables you might want to consider making available for the prompt are a $PWD (the entire path: /home/user/foo, not sure which shells), $SWD (simplified path: ~/foo, seen in Ion) , and $MWD (minimized path: /h/u/foo, seen in Fish)

[andychu]

#619 is related

[andychu]

#799 for fast command sub is related.

Since the initial version of Oil won't have func, I think we can have:

proc render-prompt(:out) {
  setref out = '> '

  # But this is also more likely

   setref out = ${.myprompt}
}

proc myprompt() {
  echo '> '
}

[andychu]

Fixed awhile ago, late announcement - https://www.oilshell.org/blog/2024/01/release-0.19.0.html