Use ExitCode in main

src/main.rs

@@ -18,7 +18,8 @@ mod rayon;
 
 #[cfg(feature = "zopfli")]
 use std::num::NonZeroU8;
-use std::{ffi::OsString, fs::DirBuilder, io::Write, path::PathBuf, process::exit, time::Duration};
+use std::process::ExitCode;
+use std::{ffi::OsString, fs::DirBuilder, io::Write, path::PathBuf, time::Duration};
 
 use clap::ArgMatches;
 mod cli;
@@ -29,7 +30,7 @@ use rayon::prelude::*;
 
 use crate::cli::DISPLAY_CHUNKS;
 
-fn main() {
+fn main() -> ExitCode {
     let matches = cli::build_command()
         // Set the value parser for filters which isn't appropriate to do in the build_command function
         .mut_arg("filters", |arg| {
@@ -43,15 +44,15 @@ fn main() {
         .get_matches_from(std::env::args());
 
     if matches.get_flag("backup") {
-        eprintln!("The --backup flag is no longer supported. Please use --out or --dir to preserve your existing files.");
-        exit(1)
+        error!("The --backup flag is no longer supported. Please use --out or --dir to preserve your existing files.");
+        return ExitCode::FAILURE;
     }
 
     let (out_file, out_dir, opts) = match parse_opts_into_struct(&matches) {
         Ok(x) => x,
         Err(x) => {
             error!("{}", x);
-            exit(1)
+            return ExitCode::FAILURE;
         }
     };
 
@@ -75,28 +76,41 @@ fn main() {
         true,
     );
 
-    let success = files.into_par_iter().filter(|(input, output)| {
-        match oxipng::optimize(input, output, &opts) {
-            // For optimizing single files, this will return the correct exit code always.
-            // For recursive optimization, the correct choice is a bit subjective.
-            // We're choosing to return a 0 exit code if ANY file in the set
-            // runs correctly.
-            // The reason for this is that recursion may pick up files that are not
-            // PNG files, and return an error for them.
-            // We don't really want to return an error code for those files.
-            Ok(_) => true,
-            Err(e) => {
-                error!("{}: {}", input, e);
-                false
+    let summary = files
+        .into_par_iter()
+        .map(|(input, output)| {
+            match oxipng::optimize(&input, &output, &opts) {
+                // For optimizing single files, this will return the correct exit code always.
+                // For recursive optimization, the correct choice is a bit subjective.
+                // We're choosing to return a 0 exit code if ANY file in the set
+                // runs correctly.
+                // The reason for this is that recursion may pick up files that are not
+                // PNG files, and return an error for them.
+                // We don't really want to return an error code for those files.
+                Ok(_) => OptimizationResult::Ok,
+                Err(e) => {
+                    error!("{input}: {e}");
+                    OptimizationResult::Failed
+                }
             }
-        }
-    });
+        })
+        .min()
+        .unwrap_or(OptimizationResult::Skipped);
 
-    if success.count() == 0 {
-        exit(1);
+    match summary {
+        OptimizationResult::Ok => ExitCode::SUCCESS,
+        OptimizationResult::Failed => ExitCode::FAILURE,
+        OptimizationResult::Skipped => ExitCode::from(3),
     }
 }
 
+#[derive(Eq, PartialEq, Ord, PartialOrd)]
+enum OptimizationResult {
+    Ok,
+    Failed,
+    Skipped,
+}
+
 fn collect_files(
     files: Vec<PathBuf>,
     out_dir: &Option<PathBuf>,