Rollup merge of #72090 - RalfJung:rustc_driver-exit-code, r=oli-obk

rustc_driver: factor out computing the exit code

In a recent Miri PR I [added a convenience wrapper](https://github.com/rust-lang/miri/pull/1405/files#diff-c3d602c5c8035a16699ce9c015bfeceaR125) around `catch_fatal_errors` and `run_compiler` that @oli-obk suggested I could upstream. However, after seeing what could be shared between `rustc_driver::main`, clippy and Miri, really the only thing I found is computing the exit code -- so that's what this PR does.

What prevents using the Miri convenience function in `rustc_driver::main` and clippy is that they do extra work inside `catch_fatal_errors`, and while I could abstract that away, clippy actually *computes the callbacks* inside there, and I fond no good way to abstract that and thus gave up. Maybe the clippy thing could be moved out, I am not sure if it ever can actually raise a `FatalErrorMarker` -- someone more knowledgeable in clippy would have to do that.

src/librustc_driver/lib.rs

@@ -1138,6 +1138,16 @@ pub fn catch_fatal_errors<F: FnOnce() -> R, R>(f: F) -> Result<R, ErrorReported>
     })
 }
 
+/// Variant of `catch_fatal_errors` for the `interface::Result` return type
+/// that also computes the exit code.
+pub fn catch_with_exit_code(f: impl FnOnce() -> interface::Result<()>) -> i32 {
+    let result = catch_fatal_errors(f).and_then(|result| result);
+    match result {
+        Ok(()) => EXIT_SUCCESS,
+        Err(_) => EXIT_FAILURE,
+    }
+}
+
 lazy_static! {
     static ref DEFAULT_HOOK: Box<dyn Fn(&panic::PanicInfo<'_>) + Sync + Send + 'static> = {
         let hook = panic::take_hook();
@@ -1228,12 +1238,12 @@ pub fn init_rustc_env_logger() {
     env_logger::init_from_env("RUSTC_LOG");
 }
 
-pub fn main() {
+pub fn main() -> ! {
     let start = Instant::now();
     init_rustc_env_logger();
     let mut callbacks = TimePassesCallbacks::default();
     install_ice_hook();
-    let result = catch_fatal_errors(|| {
+    let exit_code = catch_with_exit_code(|| {
         let args = env::args_os()
             .enumerate()
             .map(|(i, arg)| {
@@ -1246,13 +1256,8 @@ pub fn main() {
             })
             .collect::<Vec<_>>();
         run_compiler(&args, &mut callbacks, None, None)
-    })
-    .and_then(|result| result);
-    let exit_code = match result {
-        Ok(_) => EXIT_SUCCESS,
-        Err(_) => EXIT_FAILURE,
-    };
+    });
     // The extra `\t` is necessary to align this label with the others.
     print_time_passes_entry(callbacks.time_passes, "\ttotal", start.elapsed());
-    process::exit(exit_code);
+    process::exit(exit_code)
 }

src/tools/clippy/src/driver.rs

@@ -296,7 +296,7 @@ pub fn main() {
     rustc_driver::init_rustc_env_logger();
     lazy_static::initialize(&ICE_HOOK);
     exit(
-        rustc_driver::catch_fatal_errors(move || {
+        rustc_driver::catch_with_exit_code(move || {
             let mut orig_args: Vec<String> = env::args().collect();
 
             if orig_args.iter().any(|a| a == "--version" || a == "-V") {
@@ -411,7 +411,5 @@ pub fn main() {
                 if clippy_enabled { &mut clippy } else { &mut default };
             rustc_driver::run_compiler(&args, callbacks, None, None)
         })
-        .and_then(|result| result)
-        .is_err() as i32,
     )
 }