nix-instantiate --json incorrectly uses store path

[lapp0]

Describe the bug

Inconsistent output fornix-instantiate between use of --json, --xml, and no encoding argument. In the case of --json it uses the nix-store path.

Steps To Reproduce

Set imports = [(modulesPath + "/installer/scan/not-detected.nix")]; in my-file.nix

Observe the output for

# no encoding
nix-instantiate --eval -E '(import my-file.nix {config = {}; pkgs = import <nixpkgs> {}; lib = {}; modulesPath = <nixpkgs/nixos/modules>;}).imports' --strict
[ /etc/nixos/nixpkgs/nixos/modules/installer/scan/not-detected.nix ]

# xml
nix-instantiate --xml --eval -E '(import my-file.nix {config = {}; pkgs = import <nixpkgs> {}; lib = {}; modulesPath = <nixpkgs/nixos/modules>;}).imports' --strict
<?xml version='1.0' encoding='utf-8'?>
<expr>
  <list>
    <path value="/etc/nixos/nixpkgs/nixos/modules/installer/scan/not-detected.nix" />
  </list>
</expr>

# json
nix-instantiate --json --eval -E '(import my-file.nix {config = {}; pkgs = import <nixpkgs> {}; lib = {}; modulesPath = <nixpkgs/nixos/modules>;}).imports' --strict
["/nix/store/5vc99s7pn69w6mnhh7rfnzcrdl8mf7dn-not-detected.nix"]%

Expected behavior

--json output should be [ "/etc/nixos/nixpkgs/nixos/modules/installer/scan/not-detected.nix" ]

nix-env --version output

nix-env (Nix) 2.4pre20211006_53e4794

[milahu]

what exactly is in your my-file.nix file?

# my-file.nix
{ modulesPath, ... }:
{ imports = [(modulesPath + "/installer/scan/not-detected.nix")]; }

nix/src/libexpr/value-to-xml.cc

Lines 79 to 81 in 9cd8cff

	case nPath:
	doc.writeEmptyElement("path", singletonAttrs("value", v.path));
	break;

nix/src/libexpr/value-to-json.cc

Lines 34 to 36 in 9cd8cff

	case nPath:
	out.write(state.copyPathToStore(context, v.path));
	break;

... but i have no idea why json should print store paths

same for builtins.toJSON

nix-repl> (import ./my-file.nix { config = {}; pkgs = import <nixpkgs> {}; lib = {}; modulesPath = <nixpkgs/nixos/modules>; }).imports
[ /nix/var/nix/profiles/per-user/root/channels/nixos/nixos/modules/installer/scan/not-detected.nix ]

nix-repl> builtins.toJSON (import ./my-file.nix { config = {}; pkgs = import <nixpkgs> {}; lib = {};
"[\"/nix/store/5vc99s7pn69w6mnhh7rfnzcrdl8mf7dn-not-detected.nix\"]"

[ncfavier]

Just ran into this, is there any reason the JSON printer behaves differently? I can't think of a reason to copy paths to the store when printing JSON.

[ncfavier]

This is now fixed for nix eval, but not for nix-instantiate.