Warn if a Sentinel repr does not match its initial definition

Remove documentation implying that multiple definitions of Sentinel
objects are a regular occurrence

Author: HexDecimal

doc/index.rst

@@ -1042,7 +1042,6 @@ Sentinel objects
 
    If *repr* is provided, it will be used for the :meth:`~object.__repr__`
    of the sentinel object. If not provided, *name* will be used.
-   Only the initial definition of the sentinel can configure *repr*.
 
    All sentinels with the same *name* and *module_name* have the same identity.
    Sentinel objects are tested using :py:ref:`is`.

src/test_typing_extensions.py

@@ -9278,7 +9278,11 @@ def test_sentinel_repr(self):
     def test_sentinel_explicit_repr(self):
         sentinel_explicit_repr = Sentinel("sentinel_explicit_repr", repr="explicit_repr")
         self.assertEqual(repr(sentinel_explicit_repr), "explicit_repr")
-        self.assertEqual(repr(Sentinel("sentinel_explicit_repr")), "explicit_repr")
+        with self.assertWarnsRegex(
+            DeprecationWarning,
+            r"repr='sentinel_explicit_repr' conflicts with initial definition of repr='explicit_repr'"
+        ):
+            self.assertEqual(repr(Sentinel("sentinel_explicit_repr")), "explicit_repr")
 
     def test_sentinel_explicit_repr_deprecated(self):
         with self.assertWarnsRegex(
@@ -9287,7 +9291,11 @@ def test_sentinel_explicit_repr_deprecated(self):
         ):
             deprecated_repr = Sentinel("deprecated_repr", "explicit_repr")
         self.assertEqual(repr(deprecated_repr), "explicit_repr")
-        self.assertEqual(repr(Sentinel("deprecated_repr")), "explicit_repr")
+        with self.assertWarnsRegex(
+            DeprecationWarning,
+            r"repr='deprecated_repr' conflicts with initial definition of repr='explicit_repr'"
+        ):
+            self.assertEqual(repr(Sentinel("deprecated_repr")), "explicit_repr")
 
     @skipIf(sys.version_info < (3, 10), reason='New unions not available in 3.9')
     def test_sentinel_type_expression_union(self):

src/typing_extensions.py

@@ -4169,7 +4169,6 @@ class Sentinel:
 
     *repr*, if supplied, will be used for the repr of the sentinel object.
     If not provided, *name* will be used.
-    Only the initial definition of the sentinel can configure *repr*.
 
     All sentinels with the same *name* and *module_name* have the same identity.
     The ``is`` operator is used to test if an object is a sentinel.
@@ -4206,16 +4205,26 @@ def __new__(
 
         registry_key = f"{module_name}-{name}"
 
+        repr = repr if repr is not None else name
+
         # Check registered sentinels
         sentinel = _sentinel_registry.get(registry_key, None)
         if sentinel is not None:
+            if sentinel._repr != repr:
+                warnings.warn(
+                    f"repr={repr!r} conflicts with initial definition of "
+                    f"repr={sentinel._repr!r} and will be ignored"
+                    "\nUsage of repr should be consistent across definitions",
+                    DeprecationWarning,
+                    stacklevel=2,
+                )
             return sentinel
 
         # Create initial or anonymous sentinel
         sentinel = super().__new__(cls)
         sentinel._name = name
         sentinel.__module__ = module_name  # Assign which module defined this instance
-        sentinel._repr = repr if repr is not None else name
+        sentinel._repr = repr
         return _sentinel_registry.setdefault(registry_key, sentinel)
 
     def __repr__(self) -> str: