fix(cli): Define an error code policy

The main goal is to make spelling errors differentiated from other
errors.

Fixes #170

Cargo.lock

@@ -973,6 +973,15 @@ dependencies = [
  "unicode-xid 0.2.1",
 ]
 
+[[package]]
+name = "sysexit"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a26991bb0e6ef939ac9a8d6b57979efa59921928a3aa0334d818fe6e458aa6a9"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "tap"
 version = "1.0.0"
@@ -1092,6 +1101,7 @@ dependencies = [
  "predicates",
  "serde",
  "structopt",
+ "sysexit",
  "toml",
  "typos",
  "typos-dict",

Cargo.toml

@@ -48,6 +48,7 @@ env_logger = "0.8"
 bstr = "0.2"
 ahash = "0.5.8"
 difflib = "0.4"
+sysexit = "0.2"
 
 [dev-dependencies]
 assert_fs = "1.0"

src/exit.rs

@@ -0,0 +1,55 @@
+pub struct ExitCode {
+    pub code: sysexit::Code,
+    pub error: Option<anyhow::Error>,
+}
+
+impl ExitCode {
+    pub fn code(code: sysexit::Code) -> Self {
+        Self { code, error: None }
+    }
+
+    pub fn error(mut self, error: anyhow::Error) -> Self {
+        self.error = Some(error);
+        self
+    }
+}
+
+impl From<sysexit::Code> for ExitCode {
+    fn from(code: sysexit::Code) -> Self {
+        Self::code(code)
+    }
+}
+
+pub trait ChainCodeExt {
+    fn error(self) -> ExitCode;
+    fn chain(self, error: anyhow::Error) -> ExitCode;
+}
+
+impl ChainCodeExt for sysexit::Code {
+    fn error(self) -> ExitCode {
+        ExitCode::code(self)
+    }
+    fn chain(self, error: anyhow::Error) -> ExitCode {
+        ExitCode::code(self).error(error)
+    }
+}
+
+pub trait ExitCodeResultErrorExt<T> {
+    fn code(self, code: sysexit::Code) -> Result<T, ExitCode>;
+}
+
+impl<T, E: std::error::Error + Send + Sync + 'static> ExitCodeResultErrorExt<T> for Result<T, E> {
+    fn code(self, code: sysexit::Code) -> Result<T, ExitCode> {
+        self.map_err(|e| ExitCode::code(code).error(e.into()))
+    }
+}
+
+pub trait ExitCodeResultAnyhowExt<T> {
+    fn code(self, code: sysexit::Code) -> Result<T, ExitCode>;
+}
+
+impl<T> ExitCodeResultAnyhowExt<T> for Result<T, anyhow::Error> {
+    fn code(self, code: sysexit::Code) -> Result<T, ExitCode> {
+        self.map_err(|e| ExitCode::code(code).error(e))
+    }
+}

src/main.rs

@@ -11,26 +11,43 @@ mod checks;
 mod config;
 mod dict;
 mod diff;
+mod exit;
 mod replace;
 
+use exit::ChainCodeExt;
+use exit::ExitCodeResultAnyhowExt;
+use exit::ExitCodeResultErrorExt;
+
 fn main() {
     let code = match run() {
-        Ok(code) => code,
+        Ok(()) => sysexit::Code::Success,
         Err(err) => {
-            eprintln!("{}", err);
+            if let Some(error) = err.error {
-            1
+                eprintln!("{}", error);
+            }
+            err.code
         }
     };
-    std::process::exit(code);
+    std::process::exit(code as i32);
 }
 
-fn run() -> Result<i32, anyhow::Error> {
+fn run() -> Result<(), exit::ExitCode> {
-    let args = args::Args::from_args();
+    // clap's `get_matches` uses Failure rather than Usage, so bypass it for `get_matches_safe`.
+    let args = match args::Args::from_args_safe() {
+        Ok(args) => args,
+        Err(e) if e.use_stderr() => {
+            return Err(sysexit::Code::Usage.chain(e.into()));
+        }
+        Err(e) => {
+            println!("{}", e);
+            return Ok(());
+        }
+    };
 
     init_logging(args.verbose.log_level());
 
     let config = if let Some(path) = args.custom_config.as_ref() {
-        config::Config::from_file(path)?
+        config::Config::from_file(path).code(sysexit::Code::Config)?
     } else {
         config::Config::default()
     };
@@ -38,7 +55,7 @@ fn run() -> Result<i32, anyhow::Error> {
     let mut typos_found = false;
     let mut errors_found = false;
     for path in args.path.iter() {
-        let path = path.canonicalize()?;
+        let path = path.canonicalize().code(sysexit::Code::Usage)?;
         let cwd = if path.is_file() {
             path.parent().unwrap()
         } else {
@@ -47,7 +64,7 @@ fn run() -> Result<i32, anyhow::Error> {
 
         let mut config = config.clone();
         if !args.isolated {
-            let derived = config::Config::derive(cwd)?;
+            let derived = config::Config::derive(cwd).code(sysexit::Code::Config)?;
             config.update(&derived);
         }
         config.update(&args.config);
@@ -134,18 +151,18 @@ fn run() -> Result<i32, anyhow::Error> {
         }
 
         if args.diff {
-            diff_reporter.show()?;
+            diff_reporter.show().code(sysexit::Code::Unknown)?;
         } else if args.write_changes {
-            replace_reporter.write()?;
+            replace_reporter.write().code(sysexit::Code::Unknown)?;
         }
     }
 
     if errors_found {
-        Ok(2)
+        Err(sysexit::Code::Failure.error())
     } else if typos_found {
-        Ok(1)
+        Err(sysexit::Code::DataErr.error())
     } else {
-        Ok(0)
+        Ok(())
     }
 }