bug#27169: eshell/sudo doesn't work with protected directories

[npostavs]

Yegor Timoshenko <yegortimoshenko@gmail.com> writes:

>> Works for me, can you reproduce this from 'emacs -Q'?  What Emacs
>> version are you using?
>
> GNU Emacs 25.2.1 (x86_64-apple-darwin13.4.0, NS appkit-1265.21 Version 10.9.5 
> (Build 13F1911)) of 2017-04-21
>
> Yes, it's reproducible with -Q flag, provided that you execute (require 
> 'em-tramp) in *scratch* buffer.

Don't you also need (push 'eshell-tramp eshell-modules-list)?

Once I do that, I'm able to reproduce #27167, but not this bug:

    ~/src $ sudo /bin/cat foo
    /sudo:root@localhost:/home/npostavs/src/bin/cat: command not found
    ~/src $ cd /tmp
    /tmp $ sudo ls a/b
    a/b

> I believe it can be a platform-specific bug (I use macOS).

Possible.  Does this work from M-x shell?  Does C-x C-f /sudo::/tmp/a/
work?  Does it make a difference if you run from the terminal vs running
graphically (there's at least one macOS bug where this makes a
difference, #21573).