fs: check subdir correctly in cpSync

src/node_file.cc

@@ -3204,9 +3204,12 @@ static void CpSyncCheckPaths(const FunctionCallbackInfo<Value>& args) {
   }
 
   std::u8string dest_path_str = dest_path.u8string();
-
+  std::u8string src_path_str = src_path.u8string();
+  if (!src_path_str.ends_with(std::filesystem::path::preferred_separator)) {
+    src_path_str += std::filesystem::path::preferred_separator;
+  }
   // Check if dest_path is a subdirectory of src_path.
-  if (src_is_dir && dest_path_str.starts_with(src_path.u8string())) {
+  if (src_is_dir && dest_path_str.starts_with(src_path_str)) {
     std::u8string message = u8"Cannot copy " + src_path.u8string() +
                             u8" to a subdirectory of self " +
                             dest_path.u8string();

test/parallel/test-fs-cp.mjs

@@ -24,8 +24,8 @@ import tmpdir from '../common/tmpdir.js';
 tmpdir.refresh();
 
 let dirc = 0;
-function nextdir() {
-  return tmpdir.resolve(`copy_${++dirc}`);
+function nextdir(dirname) {
+  return tmpdir.resolve(dirname || `copy_${++dirc}`);
 }
 
 // Synchronous implementation of copy.
@@ -320,6 +320,45 @@ function nextdir() {
   );
 }
 
+// It must not throw error if attempt is made to copy to dest
+// directory with same prefix as src directory
+// regression test for https://github.com/nodejs/node/issues/54285
+{
+  const src = nextdir('prefix');
+  const dest = nextdir('prefix-a');
+  mkdirSync(src);
+  mkdirSync(dest);
+  cpSync(src, dest, mustNotMutateObjectDeep({ recursive: true }));
+}
+
+// It must not throw error if attempt is made to copy to dest
+// directory if the parent of dest has same prefix as src directory
+// regression test for https://github.com/nodejs/node/issues/54285
+{
+  const src = nextdir('aa');
+  const destParent = nextdir('aaa');
+  const dest = nextdir('aaa/aabb');
+  mkdirSync(src);
+  mkdirSync(destParent);
+  mkdirSync(dest);
+  cpSync(src, dest, mustNotMutateObjectDeep({ recursive: true }));
+}
+
+// It throws error if attempt is made to copy src to dest
+// when src is parent directory of the parent of dest
+{
+  const src = nextdir('a');
+  const destParent = nextdir('a/b');
+  const dest = nextdir('a/b/c');
+  mkdirSync(src);
+  mkdirSync(destParent);
+  mkdirSync(dest);
+  assert.throws(
+    () => cpSync(src, dest, mustNotMutateObjectDeep({ recursive: true })),
+    { code: 'ERR_FS_CP_EINVAL' },
+  );
+}
+
 // It throws error if attempt is made to copy to subdirectory of self.
 {
   const src = './test/fixtures/copy/kitchen-sink';