fix: detect Nix install path for fish and tcsh shell aliases (#921)

When Granted is installed via Nix, the shell scripts (assume.fish,
assume.tcsh) are placed in the share/ directory rather than bin/.
This causes the shell alias setup to generate incorrect paths for
fish and tcsh users.

This commit adds detection for Nix installations by checking if the
granted binary is located in /nix/store/. When detected, the alias
is generated with the correct path to the share/ directory.

Fixes #920

Co-authored-by: Reuben Brooks <reuben.brooks@facilitygrid.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: 3 people

pkg/alias/alias.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 
 	"github.com/AlecAivazis/survey/v2"
@@ -41,6 +42,36 @@ const devFishAlias = `alias dassume="source /usr/local/bin/dassume.fish"`
 const devTcshAlias = `alias dassume 'source /usr/local/bin/dassume.tcsh'`
 const devDefaultAlias = `alias dassume=". dassume"`
 
+// getNixSharePath returns the path to the Nix share directory if granted
+// is installed via Nix, otherwise returns an empty string.
+// Nix installs assume.fish to <store-path>/share/assume.fish rather than
+// <store-path>/bin/assume.fish
+func getNixSharePath() string {
+	execPath, err := os.Executable()
+	if err != nil {
+		return ""
+	}
+
+	// Resolve symlinks to get the real path
+	realPath, err := filepath.EvalSymlinks(execPath)
+	if err != nil {
+		return ""
+	}
+
+	// Check if we're in a Nix store path (e.g., /nix/store/xxx-granted-x.x.x/bin/granted)
+	if !strings.HasPrefix(realPath, "/nix/store/") {
+		return ""
+	}
+
+	// The Nix package structure is: /nix/store/<hash>-granted-<version>/bin/granted
+	// We need: /nix/store/<hash>-granted-<version>/share/
+	binDir := filepath.Dir(realPath)
+	storeDir := filepath.Dir(binDir)
+	shareDir := filepath.Join(storeDir, "share")
+
+	return shareDir
+}
+
 func GetDefaultAlias() string {
 	if build.IsDev() {
 		return devDefaultAlias
@@ -52,6 +83,11 @@ func GetFishAlias() string {
 		return devFishAlias
 	}
 
+	// Check if we're installed via Nix - Nix puts assume.fish in share/ not bin/
+	if nixShare := getNixSharePath(); nixShare != "" {
+		return fmt.Sprintf(`alias assume="source %s/assume.fish"`, nixShare)
+	}
+
 	// if 'brew' exists on the path, use the brew prefix rather than /usr/local/bin when installing the alias.
 	// chrnorm: there's not really a better way to determine if we've been installed with brew or not.
 	if _, err := exec.LookPath("brew"); err == nil {
@@ -65,6 +101,11 @@ func GetTcshAlias() string {
 		return devTcshAlias
 	}
 
+	// Check if we're installed via Nix - Nix puts assume.tcsh in share/ not bin/
+	if nixShare := getNixSharePath(); nixShare != "" {
+		return fmt.Sprintf(`alias assume 'source %s/assume.tcsh'`, nixShare)
+	}
+
 	// if 'brew' exists on the path, use the brew prefix rather than /usr/local/bin when installing the alias.
 	// chrnorm: there's not really a better way to determine if we've been installed with brew or not.
 	if _, err := exec.LookPath("brew"); err == nil {