GH-73991: Disallow copying directory into itself via pathlib.Path.copy()

Lib/pathlib/_abc.py

@@ -11,6 +11,7 @@
 resemble pathlib's PurePath and Path respectively.
 """
 
+import errno
 import functools
 import operator
 import posixpath
@@ -564,14 +565,33 @@ def samefile(self, other_path):
         return (st.st_ino == other_st.st_ino and
                 st.st_dev == other_st.st_dev)
 
-    def _samefile_safe(self, other_path):
+    def _ensure_different_file(self, other_path):
         """
-        Like samefile(), but returns False rather than raising OSError.
+        Raise OSError(EINVAL) if both paths refer to the same file.
         """
         try:
-            return self.samefile(other_path)
+            if not self.samefile(other_path):
+                return
         except (OSError, ValueError):
-            return False
+            return
+        err = OSError(errno.EINVAL, "Source and target are the same file")
+        err.filename = str(self)
+        err.filename2 = str(other_path)
+        raise err
+
+    def _ensure_distinct_path(self, other_path):
+        """
+        Raise OSError(EINVAL) if the other path is within this path.
+        """
+        if self == other_path:
+            err = OSError(errno.EINVAL, "Source and target are the same path")
+        elif self in other_path.parents:
+            err = OSError(errno.EINVAL, "Source path is a parent of target path")
+        else:
+            return
+        err.filename = str(self)
+        err.filename2 = str(other_path)
+        raise err
 
     def open(self, mode='r', buffering=-1, encoding=None,
              errors=None, newline=None):
@@ -826,8 +846,7 @@ def _copy_file(self, target):
         """
         Copy the contents of this file to the given target.
         """
-        if self._samefile_safe(target):
-            raise OSError(f"{self!r} and {target!r} are the same file")
+        self._ensure_different_file(target)
         with self.open('rb') as source_f:
             try:
                 with target.open('wb') as target_f:
@@ -847,6 +866,13 @@ def copy(self, target, *, follow_symlinks=True, dirs_exist_ok=False,
         """
         if not isinstance(target, PathBase):
             target = self.with_segments(target)
+        try:
+            self._ensure_distinct_path(target)
+        except OSError as err:
+            if on_error is None:
+                raise
+            on_error(err)
+            return
         stack = [(self, target)]
         while stack:
             src, dst = stack.pop()

Lib/test/test_pathlib/test_pathlib_abc.py

@@ -1823,6 +1823,12 @@ def test_copy_file_empty(self):
         self.assertTrue(target.exists())
         self.assertEqual(target.read_bytes(), b'')
 
+    def test_copy_file_to_itself(self):
+        base = self.cls(self.base)
+        source = base / 'empty'
+        source.write_bytes(b'')
+        self.assertRaises(OSError, source.copy, source)
+
     def test_copy_dir_simple(self):
         base = self.cls(self.base)
         source = base / 'dirC'
@@ -1909,6 +1915,25 @@ def test_copy_dir_to_existing_directory_dirs_exist_ok(self):
         self.assertTrue(target.joinpath('fileC').read_text(),
                         "this is file C\n")
 
+    def test_copy_dir_to_itself(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        self.assertRaises(OSError, source.copy, source)
+
+    def test_copy_dir_to_itself_on_error(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        errors = []
+        source.copy(source, on_error=errors.append)
+        self.assertEqual(len(errors), 1)
+        self.assertIsInstance(errors[0], OSError)
+
+    def test_copy_dir_into_itself(self):
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        target = base / 'dirC' / 'dirD' / 'copyC'
+        self.assertRaises(OSError, source.copy, target)
+
     def test_copy_missing_on_error(self):
         base = self.cls(self.base)
         source = base / 'foo'