From afa72b9d455d021f2cbadc8baad3cf17911fc9ee Mon Sep 17 00:00:00 2001
From: Shantanu Jain <hauntsaninja@gmail.com>
Date: Sun, 3 Nov 2024 00:53:53 -0700
Subject: [PATCH 1/2] Disallow calling type on Protocol

Fixes #16919, fixes #16890
---
 mypy/checkexpr.py                   |  9 +++++++--
 test-data/unit/check-protocols.test | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index 577576a4e5f8..c8cfd69eec7f 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -1802,10 +1802,15 @@ def check_callable_call(
 
         if (
             callee.is_type_obj()
-            and (len(arg_types) == 1)
+            and len(arg_types) == 1
             and is_equivalent(callee.ret_type, self.named_type("builtins.type"))
         ):
-            callee = callee.copy_modified(ret_type=TypeType.make_normalized(arg_types[0]))
+            proper_arg = get_proper_type(arg_types[0])
+            if isinstance(proper_arg, Instance) and proper_arg.type.is_protocol:
+                self.msg.fail("Calling type() on a protocol class is unsound", context)
+                callee = callee.copy_modified(ret_type=self.named_type("builtins.object"))
+            else:
+                callee = callee.copy_modified(ret_type=TypeType.make_normalized(arg_types[0]))
 
         if callable_node:
             # Store the inferred callable type.
diff --git a/test-data/unit/check-protocols.test b/test-data/unit/check-protocols.test
index 5ed2351e33e6..fb81d0f24c52 100644
--- a/test-data/unit/check-protocols.test
+++ b/test-data/unit/check-protocols.test
@@ -4215,3 +4215,22 @@ def g4(a: Input[bytes], b: Output[str]) -> None:
     f(a, b)  # E: Cannot infer type argument 1 of "f"
 
 [builtins fixtures/tuple.pyi]
+
+[case testTypeCallOnProtocol]
+from typing import Protocol
+
+import mod
+
+class P(Protocol):
+    def foo(self) -> None: ...
+
+a: P = mod
+value = type(a)  # E: Calling type() on a protocol class is unsound
+reveal_type(value)  # N: Revealed type is "builtins.object"
+reveal_type(value.foo)  # E: "object" has no attribute "foo" \
+                        # N: Revealed type is "Any"
+
+[file mod.py]
+def foo() -> None: ...
+
+[builtins fixtures/tuple.pyi]

From 2dc29e60b223a827bf7c9521e3f2f09d11097140 Mon Sep 17 00:00:00 2001
From: Shantanu Jain <hauntsaninja@gmail.com>
Date: Sun, 3 Nov 2024 01:31:53 -0700
Subject: [PATCH 2/2] okay, fallback because of primer hits

---
 mypy/checkexpr.py                   | 11 +++++++++--
 test-data/unit/check-protocols.test | 22 ++++++++++++++++------
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index c8cfd69eec7f..cfb983f99c37 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -1807,8 +1807,15 @@ def check_callable_call(
         ):
             proper_arg = get_proper_type(arg_types[0])
             if isinstance(proper_arg, Instance) and proper_arg.type.is_protocol:
-                self.msg.fail("Calling type() on a protocol class is unsound", context)
-                callee = callee.copy_modified(ret_type=self.named_type("builtins.object"))
+                callee = callee.copy_modified(
+                    ret_type=UnionType(
+                        [
+                            self.named_type("builtins.type"),
+                            self.named_type("types.ModuleType"),
+                            AnyType(TypeOfAny.special_form),
+                        ]
+                    )
+                )
             else:
                 callee = callee.copy_modified(ret_type=TypeType.make_normalized(arg_types[0]))
 
diff --git a/test-data/unit/check-protocols.test b/test-data/unit/check-protocols.test
index fb81d0f24c52..b9a66cf34792 100644
--- a/test-data/unit/check-protocols.test
+++ b/test-data/unit/check-protocols.test
@@ -4217,19 +4217,29 @@ def g4(a: Input[bytes], b: Output[str]) -> None:
 [builtins fixtures/tuple.pyi]
 
 [case testTypeCallOnProtocol]
-from typing import Protocol
-
-import mod
+from typing import Any, Protocol, cast
+import types
 
 class P(Protocol):
     def foo(self) -> None: ...
 
+import mod
+
 a: P = mod
-value = type(a)  # E: Calling type() on a protocol class is unsound
-reveal_type(value)  # N: Revealed type is "builtins.object"
-reveal_type(value.foo)  # E: "object" has no attribute "foo" \
+value = type(a)
+reveal_type(value)  # N: Revealed type is "Union[builtins.type, types.ModuleType, Any]"
+reveal_type(value.foo)  # E: Item "type" of "Union[type, Module, Any]" has no attribute "foo" \
                         # N: Revealed type is "Any"
 
+class Namespace: ...
+n = Namespace()
+n.foo = lambda: None  # E: "Namespace" has no attribute "foo"
+
+b: P = cast(Any, n)
+value = type(b)
+reveal_type(value)  # N: Revealed type is "Union[builtins.type, types.ModuleType, Any]"
+reveal_type(value.foo)  # E: Item "type" of "Union[type, Module, Any]" has no attribute "foo" \
+                        # N: Revealed type is "Any"
 [file mod.py]
 def foo() -> None: ...