skip dunder for missing override decorator check

Summary: fixes #3413

Reviewed By: grievejia

Differential Revision: D105349466

fbshipit-source-id: e53d0ee75ba73de07f90b59990e0d98895b4b822

Author: yangdanny97

pyrefly/lib/alt/class/class_field.rs

@@ -3600,6 +3600,7 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
         if !is_explicit_override
             && parent_attr_found
             && !parent_has_any
+            && !is_dunder(field_name.as_str())
             && class_field.can_have_override_decorator()
         {
             self.error(

pyrefly/lib/test/class_overrides.rs

@@ -1182,10 +1182,10 @@ testcase!(
     TestEnv::new().enable_missing_override_decorator_error(),
     r#"
 class Base:
-    def __str__(self) -> str: ...  # E: overrides a member in a parent class but is missing an `@override` decorator
+    def __str__(self) -> str: ...  # OK
 
 class Derived(Base):
-    def __str__(self) -> str: ...  # E: overrides a member in a parent class but is missing an `@override` decorator
+    def __str__(self) -> str: ...  # OK
     "#,
 );
 
@@ -1235,6 +1235,36 @@ class B(A):
     "#,
 );
 
+testcase!(
+    test_missing_override_decorator_dunder_from_object,
+    TestEnv::new().enable_missing_override_decorator_error(),
+    r#"
+class A:
+    def __repr__(self) -> str:
+        return "A"
+
+    def __eq__(self, other: object) -> bool:
+        return True
+
+    def __str__(self) -> str:
+        return "A"
+    "#,
+);
+
+testcase!(
+    test_missing_override_decorator_dunder_from_non_object,
+    TestEnv::new().enable_missing_override_decorator_error(),
+    r#"
+class Base:
+    def __len__(self) -> int:
+        return 0
+
+class Child(Base):
+    def __len__(self) -> int:
+        return 1
+    "#,
+);
+
 testcase!(
     test_missing_override_decorator_classvar,
     TestEnv::new().enable_missing_override_decorator_error(),

website/docs/error-kinds.mdx

@@ -1025,7 +1025,7 @@ In this example, `os.bacarat` is treated as a module name, so failing to find it
 
 ## missing-override-decorator
 
-A method overrides a parent class method but does not have the `@override` decorator.
+A method overrides a parent class method but does not have the `@override` decorator. We do not emit this error for dunder methods.
 
 This error supports strict override enforcement as specified in the [typing spec](https://typing.python.org/en/latest/spec/class-compat.html#strict-enforcement-per-project). When enabled, it requires all overriding methods to be explicitly marked with `@typing.override`.