Return ExitCode from rustc_driver::main

This makes rustc simply return an exit code from main rather than calling `std::process::exit` with an exit code. This means that drops run normally and the process exits cleanly.

Also instead of hard coding success and failure codes this uses `ExitCode::SUCCESS` and `ExitCode::FAILURE`, which in turn effectively uses `libc::EXIT_SUCCESS` and `libc::EXIT_FAILURE` (via std). These are `0` and `1` respectively for all currently supported host platforms so it doesn't actually change the exit code.

src/driver.rs

@@ -32,7 +32,7 @@ use std::env;
 use std::fs::read_to_string;
 use std::io::Write as _;
 use std::path::Path;
-use std::process::exit;
+use std::process::ExitCode;
 
 /// If a command-line option matches `find_arg`, then apply the predicate `pred` on its value. If
 /// true, then return it. The parameter is assumed to be either `--arg=value` or `--arg value`.
@@ -182,15 +182,17 @@ impl rustc_driver::Callbacks for ClippyCallbacks {
     }
 }
 
-fn display_help() {
+fn display_help() -> ExitCode {
     if writeln!(&mut anstream::stdout().lock(), "{}", help_message()).is_err() {
-        exit(rustc_driver::EXIT_FAILURE);
+        ExitCode::FAILURE
+    } else {
+        ExitCode::SUCCESS
     }
 }
 
 const BUG_REPORT_URL: &str = "https://github.com/rust-lang/rust-clippy/issues/new?template=ice.yml";
 
-pub fn main() {
+pub fn main() -> ExitCode {
     let early_dcx = EarlyDiagCtxt::new(ErrorOutputType::default());
 
     rustc_driver::init_rustc_env_logger(&early_dcx);
@@ -203,7 +205,7 @@ pub fn main() {
         dcx.handle().note(format!("Clippy version: {version_info}"));
     });
 
-    exit(rustc_driver::catch_with_exit_code(move || {
+    rustc_driver::catch_with_exit_code(move || {
         let mut orig_args = rustc_driver::args::raw_args(&early_dcx);
 
         let has_sysroot_arg = |args: &mut [String]| -> bool {
@@ -246,15 +248,15 @@ pub fn main() {
             pass_sysroot_env_if_given(&mut args, sys_root_env);
 
             rustc_driver::run_compiler(&args, &mut DefaultCallbacks);
-            return;
+            return ExitCode::SUCCESS;
         }
 
         if orig_args.iter().any(|a| a == "--version" || a == "-V") {
             let version_info = rustc_tools_util::get_version_info!();
 
-            match writeln!(&mut anstream::stdout().lock(), "{version_info}") {
-                Ok(()) => exit(rustc_driver::EXIT_SUCCESS),
-                Err(_) => exit(rustc_driver::EXIT_FAILURE),
+            return match writeln!(&mut anstream::stdout().lock(), "{version_info}") {
+                Ok(()) => ExitCode::SUCCESS,
+                Err(_) => ExitCode::FAILURE,
             }
         }
 
@@ -268,8 +270,7 @@ pub fn main() {
         }
 
         if !wrapper_mode && (orig_args.iter().any(|a| a == "--help" || a == "-h") || orig_args.len() == 1) {
-            display_help();
-            exit(0);
+            return display_help();
         }
 
         let mut args: Vec<String> = orig_args.clone();
@@ -311,7 +312,8 @@ pub fn main() {
         } else {
             rustc_driver::run_compiler(&args, &mut RustcCallbacks { clippy_args_var });
         }
-    }))
+        ExitCode::SUCCESS
+    })
 }
 
 #[must_use]