dev: support fish shell in sg

Created by: michaellzc

The problem

For 🐟 shell user, running sg start or sg setup yields unexpected errors that are hard to understand

Whenever fish users run sg setup or sg start, they will never get past the sanity check because the cli will try to source a non-existing ShellConfigPath file.

❌ Check "git" failed with the following errors:
unexpected output from git server: source: '/Users/michael' is not a file
git version 2.35.1

⋊> ~/C/s/sourcegraph on main ◦ go run ./dev/sg start                                                             15:16:46
💡 Running 4 checks...
✅ Check "docker" success!
✅ Check "redis" success!
✅ Check "postgres" success!
❌ Check "git" failed with the following errors:
unexpected output from git server: source: '/Users/michael' is not a file
git version 2.35.1

https://github.com/sourcegraph/sourcegraph/blob/df97baa8fad061107fdd7d088d6edb40f5de38d4/dev/sg/internal/usershell/usershell.go#L73-L76

https://github.com/sourcegraph/sourcegraph/blob/df97baa8fad061107fdd7d088d6edb40f5de38d4/dev/sg/internal/usershell/usershell.go#L48-L53

I started trying to get sg to work with fish. With this commit

• sg setup should work nicely with fish
• sg start will no longer error out right away provided they have followed sg setup to install all dependencies

However, they still may not be able to run Sourcegraph unless their bash environment is also configured properly. This can be verified by running SHELL=(which bash) go run ./dev/sg setup.

When running sg setup or sg start, it first tries to verify dependencies based on the $PATH available in the fish shell. However, when it comes to invoking scripts or commands defined sg.config.yaml, these commands are always run in a fresh bash shell via bash -c (this is expected because some of the scripts such as caddy only work with bash-compatible shell). This is problematic when the user doesn't have things like asdf-shim setup properly under bash but only fish. fish users will end up seeing error complaining fail to meet go or node version constraint because asdf is not configured properly in .bashrc and .tool-versions is not picked up automatically.

The workaround for fish user is first setting up the asdf and other dependencies in bash by running SHELL=(which bash) go run ./dev/sg setup, then fish users will be able to just run sg start.

Maybe we can add a warning message for fish shell users to run sg setup in bash to double-check they have the correct environment setup? An alternative is just don't support fish, and do this https://github.com/sourcegraph/sourcegraph/pull/31537

Implementation

I ended up adding a warning message during checks if user is running on unsupported shell (neither bash nor zsh) to let users know they're on an unsupported path and they should run SHELL=(which bash) sg setup to setup their environment in case of error.

Test plan

On fish shell, assuming both fish and bash has all dependencies configured properly

This should just work

go run ./dev/sg start

You should see

⋊> ~/C/s/sourcegraph on 02-19-dev_add_fish_support_to_sg ⨯ go run ./dev/sg start                                                                                                                                                             12:17:54
💡 Running 4 checks...
⚠️ You're running on unsupported shell `fish`.
⚠️ If you run into error, you may run `SHELL=(which bash) sg setup` to setup your environment.
✅ Check "docker" success!
⠹  Running check "redis"...