Improvement: Better OS error display

CHANGELOG.md

@@ -10,6 +10,10 @@ Of note:
 - The changelog 2015.5.2 has been rewritten from each commit content.
 - This file may be amended entirely in the future to adhere to the [GNU Changelog style](https://www.gnu.org/prep/standards/html_node/Style-of-Change-Logs.html#Style-of-Change-Logs)
 
+## Unversioned
+### Changed
+- Small fix to OS error outputs.
+
 ## [2018.6.3]
 ### Changed
 - Replaced [Clap](https://github.com/clap-rs/clap) with [Argh](https://github.com/google/argh) for CLI input parsing, binaries are now 300k lighter.

src/main.rs

@@ -51,7 +51,11 @@ fn main() {
   let input: String = match fetch_input(args.input) {
     Ok(input_data) => input_data,
     Err(error) => {
-      eprintln!("advent-rs: {}", error);
+      let error_str = error.to_string();
+      eprintln!(
+        "advent-rs: {}",
+        error_str.split(" (os error").next().unwrap()
+      );
       std::process::exit(1);
     }
   };

tests/cli.rs

@@ -12,6 +12,19 @@ fn invalid_year_past() -> Result<(), Box<dyn std::error::Error>> {
   Ok(())
 }
 
+#[test]
+fn non_existing_file() -> Result<(), Box<dyn std::error::Error>> {
+  let mut cmd = Command::cargo_bin("advent-rs")?;
+  cmd.arg("--year").arg("2015");
+  cmd.arg("--day").arg("01");
+  cmd.arg("non_existing_file");
+  cmd.assert().failure().stderr(predicates::str::contains(
+    "advent-rs: No such file or directory",
+  ));
+
+  Ok(())
+}
+
 #[test]
 fn calls_a_proper_test() -> Result<(), Box<dyn std::error::Error>> {
   let mut cmd = Command::cargo_bin("advent-rs")?;