Return std::process::ExitCode instead of exiting with std::process::exit

rust-lang/rust#77553 still exists on nightly-2025-01-30.

Author: taiki-e

src/cli.rs

@@ -473,7 +473,7 @@ pub(crate) fn merge_config_to_args(
 }
 
 impl Args {
-    pub(crate) fn parse() -> Result<Self> {
+    pub(crate) fn parse() -> Result<Option<Self>> {
         const SUBCMD: &str = "llvm-cov";
 
         // rustc/cargo args must be valid Unicode
@@ -775,15 +775,14 @@ impl Args {
                 }
                 Short('h') | Long("help") => {
                     print!("{}", Subcommand::help_text(subcommand));
-                    std::process::exit(0);
+                    return Ok(None);
                 }
                 Short('V') | Long("version") => {
                     if subcommand == Subcommand::None {
                         println!("{} {}", env!("CARGO_PKG_NAME"), env!("CARGO_PKG_VERSION"));
-                        std::process::exit(0);
-                    } else {
-                        unexpected("--version", subcommand)?;
+                        return Ok(None);
                     }
+                    unexpected("--version", subcommand)?
                 }
 
                 // TODO: Currently, we are using a subdirectory of the target directory as
@@ -1235,7 +1234,7 @@ impl Args {
             }
         }
 
-        Ok(Self {
+        Ok(Some(Self {
             subcommand,
             cov: LlvmCovOptions {
                 json,
@@ -1300,7 +1299,7 @@ impl Args {
             nextest_archive_file,
             cargo_args,
             rest,
-        })
+        }))
     }
 }
 

src/main.rs

@@ -12,6 +12,7 @@ use std::{
     ffi::{OsStr, OsString},
     io::{self, BufRead as _, Read as _, Write as _},
     path::Path,
+    process::ExitCode,
     time::SystemTime,
 };
 
@@ -49,18 +50,20 @@ mod fs;
 mod metadata;
 mod regex_vec;
 
-fn main() {
+fn main() -> ExitCode {
     term::init_coloring();
     if let Err(e) = try_main() {
         error!("{e:#}");
     }
     if term::error() || term::warn() && env::var_os("CARGO_LLVM_COV_DENY_WARNINGS").is_some() {
-        std::process::exit(1)
+        ExitCode::FAILURE
+    } else {
+        ExitCode::SUCCESS
     }
 }
 
 fn try_main() -> Result<()> {
-    let mut args = Args::parse()?;
+    let Some(mut args) = Args::parse()? else { return Ok(()) };
     term::verbose::set(args.verbose != 0);
 
     match args.subcommand {