ControlPath versus ProxyCommand

[Cameron Simpson]

TL;DR: I expect ProxyCommand to have effect in preference to ControlPath.

I've just tripped over this one. I have an ssh Host (let us call it "MAIN") 
with a ControlPath and with ControlMaster=no, from the .ssh/config file.

I also have a shell script whose purpose is to hop to a remote host through a 
port forward, which uses the ProxyCommand option like this:

  ProxyCommand ssh MAIN nc 127.0.0.1 7777

because the remote host is accessible via port 7777 on host MAIN.

So the script invokes an ssh commandlike this:

  ssh -o "ProxyCommand=ssh MAIN nc 127.0.0.1 7777" remoteuser at MAIN

The expectation is that the inner proxycommand ssh goes via the control socket 
and that the outer ssh uses the ProxyCommand to get to the remote host.

Imagine my surprise when the ControlMaster from the config file takes 
precedence over the ProxyCommand from the command line. By contract, this works 
as I intended:

  ssh -o ControlPath=none -o "ProxyCommand=ssh MAIN nc 127.0.0.1 7777" remoteuser at MAIN

On reflection, of course these are distinct options and that side of things 
isn't, of itself, a bug. However, is there a sane use case for using 
ControlMaster/ControlPath at all if there is a ProxyCommand? I would have 
thought not.

Can someone explain a use case for this precedence (ControlPath before 
ProxyCommand), or is this a misfeature which would benefit from a fix/change?

Thanks,
Cameron Simpson <cs at cskk.id.au> (formerly cs at zip.com.au)