nix-bash-completions: fix for non-NixOS use (#452653)

From 135798f6dff7cf5167906cecc0e9c86860c70f36 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Bj=C3=B8rn=20Forsman?= <bjorn.forsman@gmail.com>

Date: Mon, 4 Sep 2023 14:10:01 +0200

Subject: [PATCH] Fix completion with Nix 2.4+ on non-NixOS

Nix 2.4+ stopped setting NIX_PATH in the environment and instead uses a

built-in default in the C++ code (not exposed to shell processes). That

means this completion codes sees $override as empty and runs `NIX_PATH=

nix-instantiate ...`. Setting NIX_PATH to an empty string means Nix

won't use its default built-in value and completion breaks (assuming

the completion depends on '<nixpkgs>' or similar search path entries).

NixOS isn't affected because there NIX_PATH is still set (by the OS, not

by code from the Nix repo).

The fix is to not pass NIX_PATH unless we have a value for it. That

works for both old and new Nix, on NixOS and non-NixOS.

(I initially tried with a single `$maybe_nix_path nix-instantiate ...`,

but apparently bash treats the value in $maybe_nix_path as a command

instead of setting environment variables for the process.)

---

 _nix | 10 +++++++++-

 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/_nix b/_nix

index 6b9c281..61052f1 100755

--- a/_nix

+++ b/_nix

@@ -101,7 +101,15 @@ function _nix_eval_stdin () {

     # Shortcut: since the output of this function is only used in the -W argument of compgen,

     # which expects a shell-quoted list of words, we leave the double quotes from the Nix

     # output intact to approximate shell quoting.

-    NIX_PATH=$override nix-instantiate --eval - 2> /dev/null | tr '[]' ' '

+    if [[ -n "$override" ]]; then

+        NIX_PATH=$override nix-instantiate --eval - 2> /dev/null | tr '[]' ' '

+    else

+        # Don't set NIX_PATH to empty string, as that'll overwrite/clear Nix'

+        # built-in default (since version 2.4+). Nix 2.3 and older sets

+        # NIX_PATH in shell initialization files, which means for those

+        # versions we already have it in $override (code path above).

+        nix-instantiate --eval - 2> /dev/null | tr '[]' ' '

+    fi

 }

 # Resolve any urls ourselves, as nix will start downloading and block

-- 

2.50.1

      url = "https://github.com/hedning/nix-bash-completions/pull/28/commits/ef2055aa28754fa9e009bbfebc1491972e4f4e67.patch";

      hash = "sha256-TRkHrk7bX7DX0COzzYR+1pgTqLy7J55BcejNjRwthII=";

    })

    # Fix completion with Nix 2.4+ on non-NixOS: https://github.com/hedning/nix-bash-completions/pull/26

    # Rebased locally due to conflict with the above patch (https://github.com/hedning/nix-bash-completions/pull/28).

    ./0001-Fix-completion-with-Nix-2.4-on-non-NixOS.patch

  ];

  postPatch = ''