bpo-33947: dataclasses no longer can raise RecursionError in repr (GF9916) (#9970)

The reprlib code was copied here instead of importing reprlib. I'm not sure if we really need to avoid the import, but since I expect dataclasses to be more common that reprlib, it seems wise. Plus, the code is small.
(cherry picked from commit dd13c88b)
Co-authored-by: Srinivas  Thatiparthy (శ్రీనివాస్  తాటిపర్తి) <srinivasreddy@users.noreply.github.com>

Lib/dataclasses.py

@@ -5,6 +5,9 @@ import types
 import inspect
 import keyword
 import builtins
+import functools
+import _thread
+
 
 __all__ = ['dataclass',
            'field',
@@ -337,6 +340,27 @@ def _tuple_str(obj_name, fields):
     return f'({",".join([f"{obj_name}.{f.name}" for f in fields])},)'
 
 
+# This function's logic is copied from "recursive_repr" function in
+# reprlib module to avoid dependency.
+def _recursive_repr(user_function):
+    # Decorator to make a repr function return "..." for a recursive
+    # call.
+    repr_running = set()
+
+    @functools.wraps(user_function)
+    def wrapper(self):
+        key = id(self), _thread.get_ident()
+        if key in repr_running:
+            return '...'
+        repr_running.add(key)
+        try:
+            result = user_function(self)
+        finally:
+            repr_running.discard(key)
+        return result
+    return wrapper
+
+
 def _create_fn(name, args, body, *, globals=None, locals=None,
                return_type=MISSING):
     # Note that we mutate locals when exec() is called.  Caller
@@ -497,12 +521,13 @@ def _init_fn(fields, frozen, has_post_init, self_name):
 
 
 def _repr_fn(fields):
-    return _create_fn('__repr__',
-                      ('self',),
-                      ['return self.__class__.__qualname__ + f"(' +
-                       ', '.join([f"{f.name}={{self.{f.name}!r}}"
-                                  for f in fields]) +
-                       ')"'])
+    fn = _create_fn('__repr__',
+                    ('self',),
+                    ['return self.__class__.__qualname__ + f"(' +
+                     ', '.join([f"{f.name}={{self.{f.name}!r}}"
+                                for f in fields]) +
+                     ')"'])
+    return _recursive_repr(fn)
 
 
 def _frozen_get_del_attr(cls, fields):

Lib/test/test_dataclasses.py

@@ -3169,6 +3169,92 @@ class TestReplace(unittest.TestCase):
             replace(c, x=3)
         c = replace(c, x=3, y=5)
         self.assertEqual(c.x, 15)
+
+    def test_recursive_repr(self):
+        @dataclass
+        class C:
+            f: "C"
+
+        c = C(None)
+        c.f = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr.<locals>.C(f=...)")
+
+    def test_recursive_repr_two_attrs(self):
+        @dataclass
+        class C:
+            f: "C"
+            g: "C"
+
+        c = C(None, None)
+        c.f = c
+        c.g = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr_two_attrs"
+                                  ".<locals>.C(f=..., g=...)")
+
+    def test_recursive_repr_indirection(self):
+        @dataclass
+        class C:
+            f: "D"
+
+        @dataclass
+        class D:
+            f: "C"
+
+        c = C(None)
+        d = D(None)
+        c.f = d
+        d.f = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr_indirection"
+                                  ".<locals>.C(f=TestReplace.test_recursive_repr_indirection"
+                                  ".<locals>.D(f=...))")
+
+    def test_recursive_repr_indirection_two(self):
+        @dataclass
+        class C:
+            f: "D"
+
+        @dataclass
+        class D:
+            f: "E"
+
+        @dataclass
+        class E:
+            f: "C"
+
+        c = C(None)
+        d = D(None)
+        e = E(None)
+        c.f = d
+        d.f = e
+        e.f = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr_indirection_two"
+                                  ".<locals>.C(f=TestReplace.test_recursive_repr_indirection_two"
+                                  ".<locals>.D(f=TestReplace.test_recursive_repr_indirection_two"
+                                  ".<locals>.E(f=...)))")
+
+    def test_recursive_repr_two_attrs(self):
+        @dataclass
+        class C:
+            f: "C"
+            g: "C"
+
+        c = C(None, None)
+        c.f = c
+        c.g = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr_two_attrs"
+                                  ".<locals>.C(f=..., g=...)")
+
+    def test_recursive_repr_misc_attrs(self):
+        @dataclass
+        class C:
+            f: "C"
+            g: int
+
+        c = C(None, 1)
+        c.f = c
+        self.assertEqual(repr(c), "TestReplace.test_recursive_repr_misc_attrs"
+                                  ".<locals>.C(f=..., g=1)")
+
     ## def test_initvar(self):
     ##     @dataclass
     ##     class C:

Misc/NEWS.d/next/Library/2018-10-17-02-15-23.bpo-33947.SRuq3T.rst

+dataclasses now handle recursive reprs without raising RecursionError.