[PATCH] commands: possibly start a web browser during `hg serve` (BC)

[Jun Wu]

Excerpts from Gregory Szorc's message of 2016-07-17 10:27:58 -0700:
> It occurred to me while writing this that "auto launch a browser UI" is
> applicable to a number of commands, much like having command output go to a
> pager is. I could envision various commands accepting a "--browser"
> argument that would open a browser to show results instead of sending it to
> the terminal. I think the built-in web server needs a lot of love before we
> could seriously consider this, however.

Since we have "ui.interface". How about adding suboptions to it? For example:

  ui.interface.serve=browser:firefox
  ui.interface.diff=browser:luakit

It also makes it more flexible, for example, let commit -i use text, split
use ncurses by default.

It may be too flexible and can be abused as the pager though.

> Taken to its extreme, you could put a "terminal emulator" like terminal.js
> or https://hyperterm.org/  into the browser and create Jupyter Notebook
> style interactions where you type hg commands into your browser, send them
> to a command server, and render HTML results inline.