cp: refuse to copy symlink over itself

src/uu/cp/src/cp.rs

@@ -1802,7 +1802,13 @@ fn is_forbidden_to_copy_to_same_file(
     if options.copy_mode == CopyMode::SymLink && dest_is_symlink {
         return false;
     }
-    if dest_is_symlink && source_is_symlink && !options.dereference {
+    // If source and dest are both the same symlink but with different names, then allow the copy.
+    // This can occur, for example, if source and dest are both hardlinks to the same symlink.
+    if dest_is_symlink
+        && source_is_symlink
+        && source.file_name() != dest.file_name()
+        && !options.dereference
+    {
         return false;
     }
     true

tests/by-util/test_cp.rs

@@ -5218,6 +5218,31 @@ mod same_file {
         assert_eq!(symlink1, at.resolve_link(symlink2));
     }
 
+    #[test]
+    fn test_same_symlink_to_itself_no_dereference() {
+        let scene = TestScenario::new(util_name!());
+        let at = &scene.fixtures;
+        at.write(FILE_NAME, CONTENTS);
+        at.symlink_file(FILE_NAME, SYMLINK_NAME);
+        scene
+            .ucmd()
+            .args(&["-P", SYMLINK_NAME, SYMLINK_NAME])
+            .fails()
+            .stderr_contains("are the same file");
+    }
+
+    #[test]
+    fn test_same_dangling_symlink_to_itself_no_dereference() {
+        let scene = TestScenario::new(util_name!());
+        let at = &scene.fixtures;
+        at.symlink_file("nonexistent_file", SYMLINK_NAME);
+        scene
+            .ucmd()
+            .args(&["-P", SYMLINK_NAME, SYMLINK_NAME])
+            .fails()
+            .stderr_contains("are the same file");
+    }
+
     // the following tests tries to copy file to a hardlink of the same file with
     // various options
     #[test]