Previously we had the logic for this in wezterm itself; it would know
how to figure out which shell to run, or whether we should run a
different program by default (the `default_prog` setting).
This was OK, but when I added support for ssh we hit a conceptual
issue: the local side of the ssh session doesn't have any information
about the shell that should be invoked on the remote side and instead
needs to ask the remote to figure that out. The interfaces defined
in the code didn't allow for this.
This commit formalizes the concept of a default program and allows
it to be carried through to the pty layer, including over ssh sessions.
Since we now have enough smarts to figure out the local shell and the
local home dir, I've removed the logic that run `login -pf` on macos
by default; this should make the terminal startup very slightly faster
on macos, but since I'm currently on a windows system, I can only test
linux and windows on this side of this commit. I'll follow up on macos
later.
This is mostly useful for folks on Windows, as you can also run
`wezterm start ssh user@host some command` to run the `ssh` binary in a
local pty and let it manage your ssh session.
On Windows the local pty currently breaks mouse reporting
(see https://github.com/microsoft/terminal/issues/376) so it is
desirable to avoid using a local pty if we're going to talk to a
remote system.
This commit makes it a bit more convenient to establish an ad-hoc ssh
session with a pty on a remote host. This method uses libssh2 under the
covers and thus doesn't support gssapi, which is potentially frustrating
for kerberized environments, but works ok for the majority of users.
There are two issues that I want to resolve in follow up work:
* The TERM has to be sent very early in the channel establishment,
before we "know" the TERM in the `portable-pty` interface. Will need to
figure out how to specify that earlier in an appropriate way.
* Similarly, if no command is specified, we should request the use
of the shell subsystem but we don't have a way to capture this
intend with the cmdbuilder. Will need to solve this too.
This commit adds (untested!) support for remote ttys over ssh.
It requires that the embedding application connect and authenticate
the ssh session prior to turning it into a PtySystem implementation.
