cp: fail when trying to copy to read only file on mac (#5261)

* cp: fail when trying to copy to read only file

* fix spelling error in macos.rs

* simplify permissions check

* add comment

* fix typo

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

@@ -63,8 +63,15 @@ pub(crate) fn copy_on_write(
             {
                 // 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
+                if fs::metadata(dest).map_or(false, |md| !md.permissions().readonly()) {
+                    // remove and copy again
+                    // TODO: rewrite this to better match linux behavior
+                    // linux first opens the source file and destination file then uses the file
+                    // descriptors to do the clone.
+                    let _ = fs::remove_file(dest);
+                    error = pfn(src.as_ptr(), dst.as_ptr(), 0);
+                }
             }
         }
     }

tests/by-util/test_cp.rs

@@ -3440,3 +3440,19 @@ 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");
+}