internal/devbox: use exec.LookPath to find nix in --pure shell (#1869)

This fixes an issue where Devbox cannot find Nix when it's installed to
a non-default path (i.e., something other than `/nix`).

Fixes #1783.

Author: kadaan

internal/devbox/devbox.go

@@ -1243,12 +1243,12 @@ func (d *Devbox) parseEnvAndExcludeSpecialCases(currentEnv []string) (map[string
 		// Finding nix executables in path and passing it through
 		// As well as adding devbox itself to PATH
 		// Both are needed for devbox commands inside pure shell to work
-		includedInPath, err := findNixInPATH(env)
+		nixPath, err := exec.LookPath("nix")
 		if err != nil {
-			return nil, err
+			return nil, errors.New("could not find any nix executable in PATH. Make sure Nix is installed and in PATH, then try again")
 		}
-		includedInPath = append(includedInPath, dotdevboxBinPath(d))
-		env["PATH"] = envpath.JoinPathLists(includedInPath...)
+		nixPath = filepath.Dir(nixPath)
+		env["PATH"] = envpath.JoinPathLists(nixPath, dotdevboxBinPath(d))
 	}
 	return env, nil
 }

internal/devbox/pure_shell.go

@@ -4,44 +4,13 @@
 package devbox
 
 import (
-	"fmt"
 	"io/fs"
 	"os"
 	"path/filepath"
-	"strings"
 
 	"github.com/pkg/errors"
-	"go.jetpack.io/devbox/internal/debug"
-	"go.jetpack.io/devbox/internal/xdg"
 )
 
-// findNixInPATH looks for locations in PATH which nix might exist and
-// it returns a slice containing all paths that might contain nix.
-// For single-user, and multi-user installation there are default locations
-// unless XDG_* env variables are set. So we look for nix in 3 locations
-// to see if any of those exist in path.
-func findNixInPATH(env map[string]string) ([]string, error) {
-	defaultSingleUserNixBin := fmt.Sprintf("%s/.nix-profile/bin", env["HOME"])
-	defaultMultiUserNixBin := "/nix/var/nix/profiles/default/bin"
-	xdgNixBin := xdg.StateSubpath("/nix/profile/bin")
-	pathElements := strings.Split(env["PATH"], ":")
-	debug.Log("path elements: %v", pathElements)
-	nixBinsInPath := []string{}
-	for _, el := range pathElements {
-		if el == xdgNixBin ||
-			el == defaultSingleUserNixBin ||
-			el == defaultMultiUserNixBin {
-			nixBinsInPath = append(nixBinsInPath, el)
-		}
-	}
-
-	if len(nixBinsInPath) == 0 {
-		// did not find nix executable in PATH, return error
-		return nil, errors.New("could not find any nix executable in PATH. Make sure Nix is installed and in PATH, then try again")
-	}
-	return nixBinsInPath, nil
-}
-
 // Creates a symlink for devbox in .devbox/bin
 // so that devbox can be available inside a pure shell
 func createDevboxSymlink(d *Devbox) error {