NixOS should set programs.less.lessopen.default = null

[sarcasticadmin]

Issue description

When using the default pager less in NixOS, it is set to use a preprocessor calling lesspipe. lesspipe provides the following enhancements to less thus modifying less' default behavior. This behavior as a NixOS default seems unexpected.

The NixOS minimal profile already has programs.less.lessopen = mkDefault null;: 8dfe8e4

Im proposing removing any preprocessing in less by default and set programs.less.lessopen.default = null;

Steps to reproduce

$ echo $LESSOPEN # shows that less preprocessor is set
|/nix/store/2hh93jad9hlhgy2sqj4rfzsjj7c5pdf5-lesspipe-2.10/bin/lesspipe.sh %s
$ cat << EOF > example.json
{
    "glossary": {
        "title": "example glossary",
		"GlossDiv": {
            "title": "S",
			"GlossList": {
                "GlossEntry": {
                    "ID": "SGML",
					"SortAs": "SGML",
					"GlossTerm": "Standard Generalized Markup Language",
					"Acronym": "SGML",
					"Abbrev": "ISO 8879:1986",
					"GlossDef": {
                        "para": "A meta-markup language, used to create markup languages such as DocBook.",
						"GlossSeeAlso": ["GML", "XML"]
                    },
					"GlossSee": "markup"
                }
            }
        }
    }
}
EOF
$ less example.json | cat
==> (lesspipe 2.10) append : to filename to view the original json file
{
  "glossary": {
    "title": "example glossary",
    "GlossDiv": {
      "title": "S",
      "GlossList": {
        "GlossEntry": {
          "ID": "SGML",
          "SortAs": "SGML",
          "GlossTerm": "Standard Generalized Markup Language",
          "Acronym": "SGML",
          "Abbrev": "ISO 8879:1986",
          "GlossDef": {
            "para": "A meta-markup language, used to create markup languages such as DocBook.",
            "GlossSeeAlso": [
              "GML",
              "XML"
            ]
          },
          "GlossSee": "markup"
        }
      }
    }
  }
}

Note the output off less: ==> (lesspipe 2.10) append : to filename to view the original json file

You can disable the preprocessor by setting the following in your nix Configuration:

programs.less.lessopen = lib.mkDefault null;

I also had to log out of my existing session (i3) to get my profile to update after a nixos-rebuild switch. After I can confirm LESSOPEN is not set in the environment:

$ echo $LESSOPEN

$

Confirm output with less:

$ less example.json | cat
{
    "glossary": {
        "title": "example glossary",
                "GlossDiv": {
            "title": "S",
                        "GlossList": {
                "GlossEntry": {
                    "ID": "SGML",
                                        "SortAs": "SGML",
                                        "GlossTerm": "Standard Generalized Markup Language",
                                        "Acronym": "SGML",
                                        "Abbrev": "ISO 8879:1986",
                                        "GlossDef": {
                        "para": "A meta-markup language, used to create markup languages such as DocBook.",
                                                "GlossSeeAlso": ["GML", "XML"]
                    },
                                        "GlossSee": "markup"
                }
            }
        }
    }
}

Output is now the default of less without the preprocessor.

Technical details

$ nix-shell -p nix-info --run "nix-info -m"
this path will be fetched (0.00 MiB download, 0.00 MiB unpacked):
  /nix/store/vm49ygzdh61j1r39l8ikb29icwljlymn-nix-info
copying path '/nix/store/vm49ygzdh61j1r39l8ikb29icwljlymn-nix-info' from 'https://cache.nixos.org'...
 - system: `"x86_64-linux"`
 - host os: `Linux 6.6.26, NixOS, 23.11 (Tapir), 23.11.20240411.51651a5`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.18.1`
 - channels(root): `"nixos-22.05.3300.82379884b2e"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`