Avoid panic in stty

The expect() calls cause stty to panic if we are not attached to
a tty with ENOTTY. This in turn causes shells to print messages
"Aborted (core dumped)", breaking tests that assume empty stderr
[with normal stderr of the process being redirected].

Refactor the code to use .and_then() and .map_err() to map the
resulting nix Errno into a boxed UIoError.

Author: julian-klode

src/uu/stty/src/stty.rs

@@ -403,30 +403,29 @@ fn stty(opts: &Options) -> UResult<()> {
             }
         }
 
-        // TODO: Figure out the right error message for when tcgetattr fails
-        let mut termios = tcgetattr(opts.file.as_fd()).expect("Could not get terminal attributes");
-
-        // iterate over valid_args, match on the arg type, do the matching apply function
-        for arg in &valid_args {
-            match arg {
-                ArgOptions::Mapping(mapping) => apply_char_mapping(&mut termios, mapping),
-                ArgOptions::Flags(flag) => apply_setting(&mut termios, flag),
-                ArgOptions::Special(setting) => {
-                    apply_special_setting(&mut termios, setting, opts.file.as_raw_fd())?;
-                }
-                ArgOptions::Print(setting) => {
-                    print_special_setting(setting, opts.file.as_raw_fd())?;
+        tcgetattr(opts.file.as_fd())
+            .and_then(|mut termios| {
+                // iterate over valid_args, match on the arg type, do the matching apply function
+                for arg in &valid_args {
+                    match arg {
+                        ArgOptions::Mapping(mapping) => apply_char_mapping(&mut termios, mapping),
+                        ArgOptions::Flags(flag) => apply_setting(&mut termios, flag),
+                        ArgOptions::Special(setting) => {
+                            apply_special_setting(&mut termios, setting, opts.file.as_raw_fd())?;
+                        }
+                        ArgOptions::Print(setting) => {
+                            print_special_setting(setting, opts.file.as_raw_fd())?;
+                        }
+                    }
                 }
-            }
-        }
-        tcsetattr(opts.file.as_fd(), set_arg, &termios)
-            .expect("Could not write terminal attributes");
+                tcsetattr(opts.file.as_fd(), set_arg, &termios)
+            })
+            .map_err(|errno| errno.into())
     } else {
-        // TODO: Figure out the right error message for when tcgetattr fails
-        let termios = tcgetattr(opts.file.as_fd()).expect("Could not get terminal attributes");
-        print_settings(&termios, opts).expect("TODO: make proper error here from nix error");
+        tcgetattr(opts.file.as_fd())
+            .and_then(|termios| print_settings(&termios, opts))
+            .map_err(|errno| errno.into())
     }
-    Ok(())
 }
 
 fn missing_arg<T>(arg: &str) -> Result<T, Box<dyn UError>> {