Ensure we exit from copytree() when copying directory over itself.

Lib/pathlib/_abc.py

@@ -851,6 +851,7 @@ def on_error(err):
                 raise OSError(f"Cannot copy {self!r} inside itself: {target!r}")
             except OSError as err:
                 on_error(err)
+                return
         stack = [(self, target)]
         while stack:
             source_dir, target_dir = stack.pop()

Lib/test/test_pathlib/test_pathlib_abc.py

@@ -1825,6 +1825,12 @@ def test_copy_empty(self):
         self.assertTrue(target.exists())
         self.assertEqual(target.read_bytes(), b'')
 
+    def test_copy_to_itself(self):
+        base = self.cls(self.base)
+        source = base / 'empty'
+        source.write_bytes(b'')
+        self.assertRaises(OSError, source.copy, source)
+
     def test_copytree_simple(self):
         base = self.cls(self.base)
         source = base / 'dirC'
@@ -1908,6 +1914,19 @@ def test_copytree_to_existing_directory_dirs_exist_ok(self):
         self.assertTrue(target.joinpath('fileC').read_text(),
                         "this is file C\n")
 
+    def test_copytree_to_itself(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        self.assertRaises(OSError, source.copytree, source)
+
+    def test_copytree_to_itself_on_error(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        errors = []
+        source.copytree(source, on_error=errors.append)
+        self.assertEqual(len(errors), 1)
+        self.assertIsInstance(errors[0], OSError)
+
     def test_copytree_file(self):
         base = self.cls(self.base)
         source = base / 'fileA'