main: exit() only at the end

std::process::exit() was used mainly to be able to return an error code,
but it's pretty brutal (no destructors calls). This commit works around
the lack of return value for main() and calls exit() only at the very
end.

src/main.rs

@@ -34,6 +34,11 @@ use nrgrip::raw_audio;
 
 
 fn main() {
+    process::exit(main_main());
+}
+
+
+fn main_main() -> i32 {
     let args: Vec<String> = env::args().collect();
     let prog_name = &args.first().expect("Can't retrieve program's name");
 
@@ -55,13 +60,15 @@ fn main() {
     };
 
     if options.opt_present("help") {
-        exit_usage(&prog_name, &opts);
+        print_usage(&prog_name, &opts);
+        return 0;
     }
 
     // Get input NRG image name
     if options.free.len() != 1 {
         // We need exactly one input file!
-        fail_usage(&prog_name, &opts);
+        print_usage(&prog_name, &opts);
+        return 1;
     }
     let img_path = &options.free[0];
     println!("NRG image path: \"{}\"", img_path);
@@ -79,7 +86,7 @@ fn main() {
         Ok(fd) => fd,
         Err(err) => {
             println!("Can't open image file \"{}\": {}", img_path, err);
-            process::exit(1);
+            return 1;
         },
     };
 
@@ -88,7 +95,7 @@ fn main() {
         Ok(metadata) => metadata,
         Err(err) => {
             println!("Error reading \"{}\": {}", img_path, err);
-            process::exit(1);
+            return 1;
         },
     };
 
@@ -102,7 +109,7 @@ fn main() {
         println!("\nExtracting cue sheet...");
         if let Err(err) = cue_sheet::write_cue_sheet(&img_path, &metadata) {
             println!("Error writing cue sheet: {}", err);
-            process::exit(1);
+            return 1;
         }
         println!("OK!");
     }
@@ -116,18 +123,10 @@ fn main() {
         }
         println!("OK!");
     }
-}
-
 
-fn exit_usage(prog_name: &str, opts: &Options) {
-    print_usage(prog_name, opts);
-    process::exit(0);
+    0
 }
 
-fn fail_usage(prog_name: &str, opts: &Options) {
-    print_usage(prog_name, opts);
-    process::exit(1);
-}
 
 fn print_usage(prog_name: &str, opts: &Options) {
     let brief = format!("NRGrip - rip Nero Burning ROM audio images