macOS Installer doesn't handle a .zshrc file that doesn't end with a newline

[hborders]

Describe the bug

The installer appends the nix source imports directly to the end of the .zshrc file. When I run the installer on macOS 11.4 with a .zshrc file that doesn't end with a newline, the installer creates a zsh syntax error because my file ends with a fi, so my last line starts with:

fiif [

If you have a problem with a specific package or NixOS,
you probably want to file an issue at https://github.com/NixOS/nixpkgs/issues.

Steps To Reproduce

1. Create a macOS EC2 instance with the macOS 11.4 image: ami-0b3c31b0c66a46614
2. Ensure your ~/.zshrc file doesn't end in a newline
3. Run the installer in single-user mode:

sh <(curl -L https://nixos.org/nix/install) --darwin-use-unencrypted-nix-store-volume

1. Open a new terminal session
2. See error

Expected behavior

The installer handles .zshrc files that don't end in a newline. I realize that well-behaved unix text files should end with a newline, but the AWS EC2 image doesn't. Adding a newline before appending the source loading is a small price to pay.

[abathur]

I think this is the same case described in #4990 and according to #4990 (comment) there's a fix in master already that isn't backported to 2.3. If you try the numtide installer I mentioned in #4779 (comment), can you confirm that you don't see this behavior?

[hborders]

Yes, this does look the same as #4990. I'll close this.