touch/gnu compat: when touch fails because of a permission error, change the error message

+ return 1 as error code when having this error

src/uu/touch/src/touch.rs

@@ -155,6 +155,8 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
         (now, now)
     };
 
+    let mut error_code = 0;
+
     for filename in &files {
         let path = &filename[..];
 
@@ -202,14 +204,28 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
 
         if matches.is_present(options::NO_DEREF) {
             if let Err(e) = set_symlink_file_times(path, atime, mtime) {
-                show_warning!("cannot touch '{}': {}", path, e);
+                // we found an error, it should fail in any case
+                error_code = 1;
+                if e.kind() == std::io::ErrorKind::PermissionDenied {
+                    // GNU compatibility (not-owner.sh)
+                    show_error!("setting times of '{}': {}", path, "Permission denied");
+                } else {
+                    show_error!("setting times of '{}': {}", path, e);
+                }
             }
         } else if let Err(e) = filetime::set_file_times(path, atime, mtime) {
-            show_warning!("cannot touch '{}': {}", path, e);
-        }
-    }
+            // we found an error, it should fail in any case
+            error_code = 1;
 
-    0
+            if e.kind() == std::io::ErrorKind::PermissionDenied {
+                // GNU compatibility (not-owner.sh)
+                show_error!("setting times of '{}': {}", path, "Permission denied");
+            } else {
+                show_error!("setting times of '{}': {}", path, e);
+            }
+        }
+    }
+    error_code
 }
 
 fn stat(path: &str, follow: bool) -> (FileTime, FileTime) {

tests/by-util/test_touch.rs

@@ -449,3 +449,13 @@ fn test_touch_mtime_dst_fails() {
         ucmd.args(&["-m", "-t", &s, file]).fails();
     }
 }
+
+#[test]
+#[cfg(unix)]
+fn test_touch_system_fails() {
+    let (_at, mut ucmd) = at_and_ucmd!();
+    let file = "/";
+    ucmd.args(&[file])
+        .fails()
+        .stderr_contains("setting times of '/'");
+}