fix: version and completions cmd in non cargo directory

Sometimes `version` and `completions` subcommands are to run in a
directory that is not necessarily a Cargo project, for example, an IDE
plugin to check if `cargo-mutants` is installed or a shell script to
install completion for a dev env setup.

This commit allows both subcommands run inside a non Cargo project
directory.

Author: yining

src/main.rs

@@ -187,14 +187,19 @@ fn main() -> Result<()> {
 
     let options = Options::try_from(&args)?;
     // dbg!(&options);
-    let source_path = args.dir.unwrap_or_else(|| Utf8Path::new(".").to_owned());
-    let source_tree = CargoSourceTree::open(&source_path)?;
-    interrupt::install_handler();
+
     if args.version {
         println!("{} {}", NAME, VERSION);
+        return Ok(())
     } else if let Some(shell) = args.completions {
         generate(shell, &mut Cargo::command(), "cargo", &mut io::stdout());
-    } else if args.list_files {
+        return Ok(())
+    }
+
+    let source_path = args.dir.unwrap_or_else(|| Utf8Path::new(".").to_owned());
+    let source_tree = CargoSourceTree::open(&source_path)?;
+    interrupt::install_handler();
+    if args.list_files {
         list_files(&source_tree, &options, args.json)?;
     } else if args.list {
         let mutants = discover_mutants(&source_tree, &options)?;