From 5fe063eaf81724c296752bfa7bae6cd839e658ef Mon Sep 17 00:00:00 2001
From: Ryan Heard <ryanwheard@gmail.com>
Date: Fri, 9 Oct 2026 18:47:04 -0400
Subject: [PATCH] [mypyc] Reject calling a property through class object

---
 mypyc/irbuild/expression.py          | 27 ++++++++++++++
 mypyc/test-data/irbuild-classes.test | 56 ++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)

diff --git a/mypyc/irbuild/expression.py b/mypyc/irbuild/expression.py
index 8da4a38aa1ed..65486ff5c3ba 100644
--- a/mypyc/irbuild/expression.py
+++ b/mypyc/irbuild/expression.py
@@ -394,6 +394,32 @@ def check_instance_attribute_access_through_class(
                     )
 
 
+def check_property_call_through_class(
+    builder: IRBuilder, expr: CallExpr, callee: MemberExpr
+) -> None:
+    """Report error if calling a property through class object, as in "C.prop(obj)".
+
+    This always fails at runtime, since "C.prop" is a property object (or a getset
+    descriptor in a native class), but mypy may not report it. Since the getter is
+    stored as a method, we'd otherwise compile this as a direct call to the getter.
+    """
+    if isinstance(callee.expr, RefExpr):
+        node = callee.expr.node
+        typ = get_proper_type(builder.types.get(callee.expr))
+        if isinstance(typ, TypeType) and isinstance(typ.item, Instance):
+            node = typ.item.type
+        if isinstance(node, TypeInfo):
+            class_ir = builder.mapper.type_to_ir.get(node)
+            if (
+                class_ir is not None
+                and class_ir.has_method(callee.name)
+                and class_ir.method_decl(callee.name).is_prop_getter
+            ):
+                builder.error(
+                    f'Cannot call property "{callee.name}" through class object', expr.line
+                )
+
+
 def transform_super_expr(builder: IRBuilder, o: SuperExpr) -> Value:
     # warning(builder, 'can not optimize super() expression', o.line)
     sup_val = builder.load_module_attr_by_fullname("builtins.super", o.line)
@@ -499,6 +525,7 @@ def translate_method_call(builder: IRBuilder, expr: CallExpr, callee: MemberExpr
 
     This can also deal with calls to module-level functions.
     """
+    check_property_call_through_class(builder, expr, callee)
     if builder.is_native_ref_expr(callee):
         # Call to module-level native function or such
         return translate_call(builder, expr, callee)
diff --git a/mypyc/test-data/irbuild-classes.test b/mypyc/test-data/irbuild-classes.test
index 59ab6ced0391..631750284ba7 100644
--- a/mypyc/test-data/irbuild-classes.test
+++ b/mypyc/test-data/irbuild-classes.test
@@ -1388,6 +1388,62 @@ L0:
     r5 = unbox(int, r4)
     return r5
 
+[case testCallPropertyThroughClass]
+from typing import Callable, Type
+
+from mypy_extensions import mypyc_attr, trait
+
+class C:
+    _f: Callable[[int], int]
+
+    @property
+    def f(self) -> Callable[[int], int]:
+        return self._f
+
+    @property
+    def x(self) -> int:
+        return 0
+
+    @x.setter
+    def x(self, value: int) -> None:
+        pass
+
+    def m(self) -> int:
+        return 0
+
+    @classmethod
+    def g(cls, c):
+        cls.f(c)  # E: Cannot call property "f" through class object
+
+class D(C):
+    pass
+
+@trait
+class T:
+    @property
+    def p(self) -> int:
+        return 0
+
+@mypyc_attr(native_class=False)
+class N:
+    @property
+    def p(self) -> int:
+        return 0
+
+def f(c, d, t, n):
+    # mypy doesn't type check unannotated functions, so only mypyc can catch these
+    C.f(c)  # E: Cannot call property "f" through class object
+    C.x(c)  # E: Cannot call property "x" through class object
+    D.f(d)(1)  # E: Cannot call property "f" through class object
+    T.p(t)  # E: Cannot call property "p" through class object
+    N.p(n)  # E: Cannot call property "p" through class object
+
+def ok(c: C, tc: Type[C]) -> None:
+    C.f
+    C.m(c)
+    tc.m(c)
+    c.f(1)
+
 [case testBorrowResultOfCustomGetItemInIfStatement_withgil]
 from typing import List