du error output should match GNU (#1776)

* du error output should match GNU

* Created a new error macro which allows the customization of the
  "error:" string part
* Match the du output based on the type of error encountered. Can extend
  to handling other errors I guess.

* Rustfmt updates

* Added non-windows test for du no permission output

src/uu/du/src/du.rs

@@ -15,7 +15,7 @@ use chrono::Local;
 use std::collections::HashSet;
 use std::env;
 use std::fs;
-use std::io::{stderr, Result, Write};
+use std::io::{stderr, ErrorKind, Result, Write};
 use std::iter;
 #[cfg(not(windows))]
 use std::os::unix::fs::MetadataExt;
@@ -296,7 +296,21 @@ fn du(
                             }
                         }
                     }
-                    Err(error) => show_error!("{}", error),
+                    Err(error) => match error.kind() {
+                        ErrorKind::PermissionDenied => {
+                            let description = format!(
+                                "cannot access '{}'",
+                                entry
+                                    .path()
+                                    .as_os_str()
+                                    .to_str()
+                                    .unwrap_or("<Un-printable path>")
+                            );
+                            let error_message = "Permission denied";
+                            show_error_custom_description!(description, "{}", error_message)
+                        }
+                        _ => show_error!("{}", error),
+                    },
                 },
                 Err(error) => show_error!("{}", error),
             }

src/uucore/src/lib/macros.rs

@@ -31,6 +31,14 @@ macro_rules! show_error(
 );
 
 /// Show a warning to stderr in a silimar style to GNU coreutils.
+#[macro_export]
+macro_rules! show_error_custom_description (
+    ($err:expr,$($args:tt)+) => ({
+        eprint!("{}: {}: ", executable!(), $err);
+        eprintln!($($args)+);
+    })
+);
+
 #[macro_export]
 macro_rules! show_warning(
     ($($args:tt)+) => ({

tests/by-util/test_du.rs

@@ -190,3 +190,33 @@ fn test_du_time() {
     assert_eq!(result.stderr, "");
     assert_eq!(result.stdout, "0\t2015-05-15 00:00\tdate_test\n");
 }
+
+#[cfg(not(target_os = "windows"))]
+#[cfg(feature = "chmod")]
+#[test]
+fn test_du_no_permission() {
+    let ts = TestScenario::new("du");
+
+    let chmod = ts.ccmd("chmod").arg("-r").arg(SUB_DIR_LINKS).run();
+    println!("chmod output: {:?}", chmod);
+    assert!(chmod.success);
+    let result = ts.ucmd().arg(SUB_DIR_LINKS).run();
+
+    ts.ccmd("chmod").arg("+r").arg(SUB_DIR_LINKS).run();
+
+    assert!(result.success);
+    assert_eq!(
+        result.stderr,
+        "du: cannot read directory ‘subdir/links‘: Permission denied (os error 13)\n"
+    );
+    _du_no_permission(result.stdout);
+}
+
+#[cfg(target_vendor = "apple")]
+fn _du_no_permission(s: String) {
+    assert_eq!(s, "0\tsubdir/links\n");
+}
+#[cfg(all(not(target_vendor = "apple"), not(target_os = "windows")))]
+fn _du_no_permission(s: String) {
+    assert_eq!(s, "4\tsubdir/links\n");
+}