mise-nix breaks XDG_DATA_DIRS if a nix package has /share path

[pasha-kuznetsov]

Steps to reproduce

mise use -g nix:most
mise activate fish | source

Observed behavior

XDG_DATA_DIRS only includes the nix-most /share dir:

> echo $XDG_DATA_DIRS
~/.local/share/mise/installs/nix-most/5.2.0/share

Expected behavior

XDG_DATA_DIRS to include both the prior dirs, and the nix-most /share dir, something along these lines:

> echo $XDG_DATA_DIRS
~/.local/share/flatpak/exports/share ~/exports/share /usr/local/share /usr/share ~/.nix-profile/share /nix/var/nix/profiles/default/share ~/.local/share/mise/installs/nix-most/5.2.0/share

Why

This is critical for most applications to continue working.

What's broken

mise hook-env -s fish contains the following lines:

set -gx PATH ...
set -gx XDG_DATA_DIRS ~/.local/share/mise/installs/nix-most/5.2.0/share
set -gx HOST_PATH '/nix/store...

And the culprit appears to be this code:

mise-nix/lib/nix_env.lua

Line 233 in e310c4c

table.insert(env_vars, { key = "XDG_DATA_DIRS", value = share_path })

  -- XDG_DATA_DIRS
  local share_path = real_path .. "/share"
  local has_share = cmd.exec("test -d '" .. share_path .. "' && echo yes || echo no"):match("yes")
  if has_share then
    table.insert(env_vars, { key = "XDG_DATA_DIRS", value = share_path })
  end

  return env_vars

Which is eventually returned from PLUGIN:BackendExecEnv, resulting in mise resetting XDG_DATA_DIRS.

Fix

mise-nix should collect the pre-existing XDG_DATA_DIRS value, and append the package /share path.

[jbadeau]

let me have a look. thanx for reporting