nix-env's generated manifest accidentally pretty-prints, breaking the manifest.

[grahamc]

Describe the bug

After installing some software I got:

$ nix-env -iA nixpkgs.shfmt
installing 'shfmt-3.4.3'
error: file 'REPEAT' was not found in the Nix search path (add it using $NIX_PATH or -I)

       at /nix/store/8klaa4whhxs08a55w92rnyx45bx30jdy-env-manifest.nix:1:15589:

Looking in the file, we saw:

platforms = <REPEAT>;

Steps To Reproduce

Install a bunch of software with nix-env until you get this REPEAT behavior.

Expected behavior

The generated manifest should be valid, and not attempt to pretty-print.

nix-env --version output

$ nix --version
nix (Nix) 2.8.0

Additional context n/a

[pbsds]

nix-env (Nix) 2.7.0