feat: remove unsafe rust

src/main.rs

···
-use std::{env, path::PathBuf};
+use std::path::PathBuf;
 
 use clap::Parser;
 use color_eyre::Result;
···
     let after = args.after;
     let lix_bin = args.lix_bin;
 
+    let mut lix_exe = None;
     if let Some(lix_bin) = lix_bin {
-        let current_path = env::var_os("PATH").unwrap();
-        let current_path = env::split_paths(&current_path);
-        let new_path = std::iter::once(lix_bin).chain(current_path);
-        let new_path = env::join_paths(new_path).unwrap();
-        unsafe {
-            env::set_var("PATH", &new_path);
+        lix_exe = if lix_bin.is_dir() {
+            Some(lix_bin.join("nix"))
+        } else {
+            Some(lix_bin)
         }
     }
 
···
         std::process::exit(1);
     }
 
-    let packages: PackageListDiff = DiffRoot::new(&before, &after)?.into();
+    let packages: PackageListDiff = DiffRoot::new(lix_exe, &before, &after)?.into();
 
     let arrow_style = Style::new().bold().fg(Color::LightGray);
 

src/parser.rs

···
 use color_eyre::Result;
+use serde::de::Deserializer;
 use serde::Deserialize;
-use serde::de::Deserializer;
-use std::{borrow::Cow, collections::BTreeMap, path::Path, process::Command};
+use std::{
+    borrow::Cow,
+    collections::BTreeMap,
+    path::{Path, PathBuf},
+    process::Command,
+};
 
 #[derive(Deserialize, Debug)]
 pub struct DiffRoot {
···
 }
 
 impl DiffRoot {
-    pub fn new(before: &Path, after: &Path) -> Result<DiffRoot> {
-        let raw_diff = Command::new("nix")
+    pub fn new(lix_path: Option<PathBuf>, before: &Path, after: &Path) -> Result<DiffRoot> {
+        let lix_exe;
+        if let Some(lix_path) = lix_path {
+            lix_exe = lix_path;
+        } else {
+            lix_exe = "nix".into();
+        };
+
+        let raw_diff = Command::new(lix_exe)
             .args(["store", "diff-closures", "--json"])
             .args([before, after])
             .output()?;