cp: fail when trying to copy to read only file on mac

src/uu/cp/src/platform/macos.rs

@@ -63,8 +63,23 @@
             {
                 // clonefile(2) fails if the destination exists.  Remove it and try again.  Do not
                 // bother to check if removal worked because we're going to try to clone again.
-                let _ = fs::remove_file(dest);
-                error = pfn(src.as_ptr(), dst.as_ptr(), 0);
+                // first lets make sure the dest file is not read only
+                match fs::metadata(dest) {
+                    Ok(md) => {
+                        if md.permissions().readonly() {
+                            return Err(format!(
+                                "failed to clone {source:?} from {dest:?}: permission denied"
+                            )
+                            .into());
+                        } else {
+                            let _ = fs::remove_file(dest);
+                            error = pfn(src.as_ptr(), dst.as_ptr(), 0);
+                        }
+                    }
+                    Err(e) => {
+                        return Err(format!("failed to clone {source:?} from {dest:?}: {e}").into());
+                    }
+                }
             }
         }
     }

tests/by-util/test_cp.rs

@@ -3243,3 +3243,19 @@ fn test_cp_only_source_no_target() {
         panic!("Failure: stderr was \n{stderr_str}");
     }
 }
+
+#[test]
+fn test_cp_dest_no_permissions() {
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+
+    at.touch("valid.txt");
+    at.touch("invalid_perms.txt");
+    at.set_readonly("invalid_perms.txt");
+
+    ts.ucmd()
+        .args(&["valid.txt", "invalid_perms.txt"])
+        .fails()
+        .stderr_contains("invalid_perms.txt")
+        .stderr_contains("denied");
+}