From 00bcb11e199251c4313c74bac77083d3e98eb88a Mon Sep 17 00:00:00 2001
From: Yurii Karabas <1998uriyyo@gmail.com>
Date: Tue, 7 Sep 2021 17:14:35 +0300
Subject: [PATCH 1/5] bpo-45121: Fix issue when Protocol.__init__ raise
 RecursionError

---
 Lib/test/test_typing.py                                | 10 ++++++++++
 Lib/typing.py                                          |  6 ++++++
 .../2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst           |  2 ++
 3 files changed, 18 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 847d583cdafb9a..36327bd40dbe1c 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -1610,6 +1610,16 @@ class P(Protocol):
         with self.assertRaisesRegex(TypeError, "@runtime_checkable"):
             isinstance(1, P)
 
+    def test_super_call_init(self):
+        class P(Protocol):
+            x: int
+
+        class Foo(P):
+            def __init__(self):
+                super().__init__()
+
+        Foo()
+
 
 class GenericTests(BaseTestCase):
 
diff --git a/Lib/typing.py b/Lib/typing.py
index 892f1b3506851d..c8422ce022cfa9 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1406,6 +1406,12 @@ def _no_init_or_replace_init(self, *args, **kwargs):
     if cls._is_protocol:
         raise TypeError('Protocols cannot be instantiated')
 
+    # When `_no_init_or_replace_init` called using super() there are no
+    # need to calculate correct `__init__` method to call.
+    # see bpo-45121
+    if cls.__init__ is not _no_init_or_replace_init:
+        return
+
     # Initially, `__init__` of a protocol subclass is set to `_no_init_or_replace_init`.
     # The first instantiation of the subclass will call `_no_init_or_replace_init` which
     # searches for a proper new `__init__` in the MRO. The new `__init__`
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst b/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst
new file mode 100644
index 00000000000000..9eef91c5d99e3c
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst	
@@ -0,0 +1,2 @@
+Fix issue when ``Protocol.__init__`` raise ``RecursionError`` when it called
+using ``super()``. Patch provided by Yurii Karabas.

From 54ec43d97d22e546320bf53865f0c75cc1fdb5b3 Mon Sep 17 00:00:00 2001
From: Yurii Karabas <1998uriyyo@gmail.com>
Date: Tue, 7 Sep 2021 17:52:39 +0300
Subject: [PATCH 2/5] Update Misc/NEWS.d/next/Core and
 Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst

Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>
---
 .../Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst b/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst
index 9eef91c5d99e3c..ce4a513d130371 100644
--- a/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst	
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst	
@@ -1,2 +1,2 @@
-Fix issue when ``Protocol.__init__`` raise ``RecursionError`` when it called
+Fix issue where ``Protocol.__init__`` raises ``RecursionError`` when called
 using ``super()``. Patch provided by Yurii Karabas.

From 79cfef0566c6c4d3ee01df8dd86d80a1dfe84bbe Mon Sep 17 00:00:00 2001
From: Yurii Karabas <1998uriyyo@gmail.com>
Date: Tue, 7 Sep 2021 18:06:34 +0300
Subject: [PATCH 3/5] Add comment

---
 Lib/test/test_typing.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 36327bd40dbe1c..fa49b90886c302 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -1618,7 +1618,7 @@ class Foo(P):
             def __init__(self):
                 super().__init__()
 
-        Foo()
+        Foo()  # Previously triggered RecursionError
 
 
 class GenericTests(BaseTestCase):

From 77d9c607b185bbc18b069518fd4d6c8204631e57 Mon Sep 17 00:00:00 2001
From: Yurii Karabas <1998uriyyo@gmail.com>
Date: Tue, 7 Sep 2021 22:54:06 +0300
Subject: [PATCH 4/5] Update comments

---
 Lib/typing.py                                                | 5 ++---
 .../2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst                 | 4 ++--
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/Lib/typing.py b/Lib/typing.py
index c8422ce022cfa9..e29d699283dfec 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1406,9 +1406,8 @@ def _no_init_or_replace_init(self, *args, **kwargs):
     if cls._is_protocol:
         raise TypeError('Protocols cannot be instantiated')
 
-    # When `_no_init_or_replace_init` called using super() there are no
-    # need to calculate correct `__init__` method to call.
-    # see bpo-45121
+    # Already using a custom `__init__`. No need to calculate correct
+    # `__init__` to call. This can lead to RecursionError. See bpo-45121.
     if cls.__init__ is not _no_init_or_replace_init:
         return
 
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst b/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst
index ce4a513d130371..8959dafcfd6586 100644
--- a/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst	
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst	
@@ -1,2 +1,2 @@
-Fix issue where ``Protocol.__init__`` raises ``RecursionError`` when called
-using ``super()``. Patch provided by Yurii Karabas.
+Fix issue when ``Protocol.__init__`` raises ``RecursionError`` when it
+called directly or via ``super()``. Patch provided by Yurii Karabas.

From 9eae697b5385058c4ad2e145e8b7f6e21ca64c3b Mon Sep 17 00:00:00 2001
From: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>
Date: Wed, 8 Sep 2021 17:47:08 +0800
Subject: [PATCH 5/5] Fix news grammar

---
 .../Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst b/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst
index 8959dafcfd6586..19eb3314125167 100644
--- a/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst	
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-09-07-17-10-16.bpo-45121.iG-Hsf.rst	
@@ -1,2 +1,2 @@
-Fix issue when ``Protocol.__init__`` raises ``RecursionError`` when it
+Fix issue where ``Protocol.__init__`` raises ``RecursionError`` when it's
 called directly or via ``super()``. Patch provided by Yurii Karabas.