Support tcsh

[jyn514]

Describe the problem you are trying to solve
The environment variable script in ~/.cargo/env does not support tcsh.

Describe the solution you'd like
Either have two different scripts depending on the shell detected, or add 'compatibility' using something like https://superuser.com/a/373964/709183.

Notes
I'm fine if the shell isn't determined automatically as long as there's a way to select a different one.

I can go in and edit the env file by hand, but it's annoying.

[workingjubilee]

Going to fix this as part of #2106 (comment), any further pointers you can provide on tcsh and how *BSD environments handle rcfiles and env vars is appreciated.

[kinnison]

I'm inclined to say "You chose to shoot yourself in the foot by using a *csh, you get to keep all the splattered bloody bone fragments" but if @workingjubilee wants to have a go at supporting them too then I won't stop them.

We'd need a env.sh and env.csh because they use fundamentally different syntaxes for controlling environment variables (export vs setenv for example). If we're going to do this then we should probably also embrace the other popular non-POSIX shell out there and have an env.fish (blech)

[workingjubilee]

To be clear, I don't have the faintest of how fish works, aside from "surprisingly differently", so while I will probably engage a refactoring step that will make it easier to add stuff for the fish shell, I have no firm intention of making it work.

[workingjubilee]

@rustbot label: +O-bsd

[jyn514]

@workingjubilee this is unrelated to BSD, you can install tcsh on any machine. In my case this was CentOS 8, but I've used it on ubuntu as well.

[jyn514]

@rustbot label: -O-bsd

[jyn514]

I think this is a misfeature tbh.