Julia REPL should show environment name inline

[kdheepak]

Currently, without any changes to startup.jl, running julia from the command activates the root environment. I think this is a poor UX but it exists for safety reasons ( we don't want julia -e "using Foo" to load arbitrary malicious code ).

In internal documentation, I've recommended using julia --project=. as the default way new users should start a REPL.

But it can be easy to fat finger this and you can end up nesting levels a folder level. Here's an example I've seen people do accidentally:

Here's another screenshot I took of a colleague's computer from this morning, where they forgot to add a . in @.:

I think if the prompt has some indication of what the environment was, it would have been more clear to my colleague without me intervening. I've seen new users run into this issue enough times that I think it is worth making some UX change to the Julia REPL to improve the situation.

I particularly like how in conda, the environment is always listed as part of the shell:

(base) C:\Users\USERNAME\gitrepos\empty-new-folder>conda activate projectx

(projectx) C:\Users\USERNAME\gitrepos\empty-new-folder>

We don't have to go that far as to make the shell aware of Julia but making a prompt inside the Julia REPL more user friendly would be an improvement imho.

If we wanted to preserve space, we can leave the display as is for shorter terminal widths but with wider terminals are available, we can print the environment name on the right hand side. e.g.:

julia>                                         <(projectx)