Return ExitCode from driver::main() (#23)

Closes #17!

bevy_lint/src/driver.rs

@@ -1,14 +1,17 @@
 //! Contains code related to writing `bevy_lint_driver`.
 
 use crate::callback::BevyLintCallback;
+use std::process::ExitCode;
 
 /// This is the main entrypoint into the driver, exported so that `bevy_cli` may call it.
-#[allow(clippy::result_unit_err)]
-pub fn main() -> Result<(), ()> {
+pub fn main() -> ExitCode {
     let args: Vec<String> = dbg!(std::env::args().skip(1).collect());
 
     // Call the compiler with our custom callback.
-    rustc_driver::RunCompiler::new(&args, &mut BevyLintCallback)
-        .run()
-        .map_err(|_| ())
+    let result = rustc_driver::RunCompiler::new(&args, &mut BevyLintCallback).run();
+
+    match result {
+        Ok(_) => ExitCode::SUCCESS,
+        Err(_) => ExitCode::FAILURE,
+    }
 }

src/lint_driver.rs

@@ -5,6 +5,8 @@
 // opt-in to `rustc_private`.
 #![feature(rustc_private)]
 
-fn main() -> Result<(), ()> {
+use std::process::ExitCode;
+
+fn main() -> ExitCode {
     bevy_lint::driver::main()
 }