From 768ce5bb66605e298449f4c5626d5a9b1399d455 Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Tue, 21 Dec 2021 12:40:38 +0000
Subject: [PATCH] Allow calling a function with name '_' (#11810)

Fixes #11774. The issue has relevant background information in the
discussion.

It may be worth it to eventually add back some restrictions, but we'd
only focus the restrictions on singledispatch functions. This is a
quick fix to work around a regression.
---
 mypy/checkexpr.py                   | 7 -------
 test-data/unit/check-functions.test | 6 ++++++
 test-data/unit/check-redefine.test  | 3 ++-
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index 1647339ef217..dfac5be27d95 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -1,6 +1,5 @@
 """Expression type checker. This file is conceptually part of TypeChecker."""
 
-from mypy.util import unnamed_function
 from mypy.backports import OrderedDict, nullcontext
 from contextlib import contextmanager
 import itertools
@@ -347,12 +346,6 @@ def visit_call_expr_inner(self, e: CallExpr, allow_none_return: bool = False) ->
                 and callee_type.implicit):
             self.msg.untyped_function_call(callee_type, e)
 
-        if (isinstance(callee_type, CallableType)
-                and not callee_type.is_type_obj()
-                and unnamed_function(callee_type.name)):
-            self.msg.underscore_function_call(e)
-            return AnyType(TypeOfAny.from_error)
-
         # Figure out the full name of the callee for plugin lookup.
         object_type = None
         member = None
diff --git a/test-data/unit/check-functions.test b/test-data/unit/check-functions.test
index 6f69a1fe25bc..bdf75b2dc58c 100644
--- a/test-data/unit/check-functions.test
+++ b/test-data/unit/check-functions.test
@@ -2230,6 +2230,12 @@ reveal_type(h) # N: Revealed type is "builtins.function"
 h(7) # E: Cannot call function of unknown type
 [builtins fixtures/bool.pyi]
 
+[case testFunctionWithNameUnderscore]
+def _(x: int) -> None: pass
+
+_(1)
+_('x')  # E: Argument 1 to "_" has incompatible type "str"; expected "int"
+
 -- Positional-only arguments
 -- -------------------------
 
diff --git a/test-data/unit/check-redefine.test b/test-data/unit/check-redefine.test
index d2229dba470f..85208df0932a 100644
--- a/test-data/unit/check-redefine.test
+++ b/test-data/unit/check-redefine.test
@@ -498,7 +498,8 @@ def _(arg: str):
 def _(arg: int) -> int:
     return 'a' # E: Incompatible return value type (got "str", expected "int")
 
-[case testCallingUnderscoreFunctionIsNotAllowed]
+[case testCallingUnderscoreFunctionIsNotAllowed-skip]
+# Skipped because of https://github.com/python/mypy/issues/11774
 def _(arg: str) -> None:
     pass