Read full lines when asking for user input when TERM=dumb

[arvidj]

Fixes #6828

[kit-ty-kate]

That looks alright on principle. Although i believe that the problem is more that your terminal doesn't support termio's non-canonical mode so a real fix could be to both test the TERM variable and if it's not dumb then test for non-canonical mode.

However that said, i'm wondering if we couldn't simplify all this and just use the simple mode all the time. This would match better with the typical unix input method. @rjbou @dra27 what do you think?

[arvidj]

ok, maybe something like:

    if OpamStd.Sys.(not tty_out || os () = Win32 || os () = Cygwin ||
                      Lazy.force dumb_term || (Unix.tcgetattr stdin).c_icanon)
    then

?

[kit-ty-kate]

yeah that's what i was thinking about

[kit-ty-kate]

Actually i just tested it in M-x shell and it wouldn't work. c_icanon still appears false even if the current terminal session doesn't support it

[kit-ty-kate]

I think this will do the job just fine for now and is correct anyway. We can improve it later i think (see #6830)

[kit-ty-kate]

@arvidj i've squashed and renamed the commit/PR. If you're happy with it feel free to mark this PR ready to review and i'll merge it