From 754596cb7fd36230376a9aa96cfa07b79a627467 Mon Sep 17 00:00:00 2001
From: hauntsaninja <hauntsaninja@gmail.com>
Date: Wed, 5 Mar 2025 13:05:38 -0800
Subject: [PATCH 1/2] stubtest: better checking of runtime args with dunder
 names

Fixes #15302, fixes #14560
---
 mypy/stubtest.py          |  6 ++----
 mypy/test/teststubtest.py | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/mypy/stubtest.py b/mypy/stubtest.py
index 89af8e465464..a444cdf83af4 100644
--- a/mypy/stubtest.py
+++ b/mypy/stubtest.py
@@ -654,10 +654,7 @@ def _verify_arg_name(
     if is_dunder(function_name, exclude_special=True):
         return
 
-    def strip_prefix(s: str, prefix: str) -> str:
-        return s.removeprefix(prefix)
-
-    if strip_prefix(stub_arg.variable.name, "__") == runtime_arg.name:
+    if stub_arg.variable.name == runtime_arg.name or stub_arg.variable.name.removeprefix("__") == runtime_arg.name:
         return
 
     nonspecific_names = {"object", "args"}
@@ -948,6 +945,7 @@ def _verify_signature(
         if (
             runtime_arg.kind != inspect.Parameter.POSITIONAL_ONLY
             and (stub_arg.pos_only or stub_arg.variable.name.startswith("__"))
+            and not runtime_arg.name.startswith("__")
             and stub_arg.variable.name.strip("_") != "self"
             and not is_dunder(function_name, exclude_special=True)  # noisy for dunder methods
         ):
diff --git a/mypy/test/teststubtest.py b/mypy/test/teststubtest.py
index 099e7605eea2..07dda2696db0 100644
--- a/mypy/test/teststubtest.py
+++ b/mypy/test/teststubtest.py
@@ -339,6 +339,22 @@ def __exit__(self, exc_type, exc_val, exc_tb): pass
             """,
             error=None,
         )
+        yield Case(
+            stub="""def dunder_name(__x: int) -> None: ...""",
+            runtime="""def dunder_name(__x: int) -> None: ...""",
+            error=None,
+        )
+        yield Case(
+            stub="""def dunder_name_posonly(__x: int, /) -> None: ...""",
+            runtime="""def dunder_name_posonly(__x: int) -> None: ...""",
+            error=None,
+        )
+        yield Case(
+            stub="""def dunder_name_bad(x: int) -> None: ...""",
+            runtime="""def dunder_name_bad(__x: int) -> None: ...""",
+            error="dunder_name_bad",
+        )
+
 
     @collect_cases
     def test_arg_kind(self) -> Iterator[Case]:

From 969cc0f88611a1db3bad36423b0e1c9eaeb8764a Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Wed, 5 Mar 2025 21:07:44 +0000
Subject: [PATCH 2/2] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 mypy/stubtest.py          | 5 ++++-
 mypy/test/teststubtest.py | 1 -
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/mypy/stubtest.py b/mypy/stubtest.py
index a444cdf83af4..a0f886106715 100644
--- a/mypy/stubtest.py
+++ b/mypy/stubtest.py
@@ -654,7 +654,10 @@ def _verify_arg_name(
     if is_dunder(function_name, exclude_special=True):
         return
 
-    if stub_arg.variable.name == runtime_arg.name or stub_arg.variable.name.removeprefix("__") == runtime_arg.name:
+    if (
+        stub_arg.variable.name == runtime_arg.name
+        or stub_arg.variable.name.removeprefix("__") == runtime_arg.name
+    ):
         return
 
     nonspecific_names = {"object", "args"}
diff --git a/mypy/test/teststubtest.py b/mypy/test/teststubtest.py
index 07dda2696db0..492897d33a4a 100644
--- a/mypy/test/teststubtest.py
+++ b/mypy/test/teststubtest.py
@@ -355,7 +355,6 @@ def __exit__(self, exc_type, exc_val, exc_tb): pass
             error="dunder_name_bad",
         )
 
-
     @collect_cases
     def test_arg_kind(self) -> Iterator[Case]:
         yield Case(