If the script doesn't have a shebang I'd be extremely suspicious of it. If it does include a shebang, it will run under the chosen interpreter and your login or default shell won't matter.
If it's something you're trying to `source` then it can go wrong, but `bass` takes care of that if it's a POSIX-compatible script being sourced. If it's some other sort of script being sourced (PowerShell, NuShell, etc) you can have issues, though `fish` will usually fail to parse it and exit with error.
If it's something you're trying to `source` then it can go wrong, but `bass` takes care of that if it's a POSIX-compatible script being sourced. If it's some other sort of script being sourced (PowerShell, NuShell, etc) you can have issues, though `fish` will usually fail to parse it and exit with error.