Install script tells me to source a sh-style env file when run in fish

[lgarron]

Problem

At the end of install, rustup helpfully tries to tell me:

To configure your current shell, run:
source "/Users/lgarron/.data/cargo/env"`

But my current shell is fish, and sourcing that file is going to be a bad time:

> source "/Users/lgarron/.data/cargo/env"
~/.data/cargo/env (line 4): 'case' builtin not inside of switch block
case ":${PATH}:" in
^~~^
from sourcing file ~/.data/cargo/env
source: Error while reading file '/Users/lgarron/.data/cargo/env'

Steps

1. Open a fish terminal on the latest macOS.
2. Run the command from https://rustup.rs/ (curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh)

Possible Solution(s)

1. Don't tell me that something will configure my current shell, if it in fact does not?
2. For maximum helpfulness, offer a fish-compatible env file that I can source.

Notes

No response

Rustup version

> rustup --version
rustup 1.25.2 (17db695f1 2023-02-01)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.67.1 (d5a82bbd2 2023-02-07)

### Installed toolchains

```console
> rustup show
Default host: aarch64-apple-darwin
rustup home:  /Users/lgarron/.data/rustup

stable-aarch64-apple-darwin (default)
rustc 1.67.1 (d5a82bbd2 2023-02-07)

[rbtcollins]

It is an interesting idea to walk up the process tree / look for some indication that fish is in use and change our prompts. See also #478. That said, you are actually running the install in posix sh, not fish - thats what the curlsh pattern does. I'm going to duplicate all the fish bugs together.