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Warn user not to override special magic methods #6625

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Merged
youknowone merged 1 commit into from
Jan 2, 2026
Merged

Warn user not to override special magic methods #6625

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106 changes: 97 additions & 9 deletions crates/derive-impl/src/pyclass.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -909,18 +909,106 @@ where

let py_name = item_meta.method_name()?;

// Disallow __new__ and __init__ as pymethod in impl blocks (not in traits)
// Disallow slot methods - they should be defined via trait implementations
// These are exposed as wrapper_descriptor via add_operators from SLOT_DEFS
if !args.context.is_trait {
if py_name == "__new__" {
return Err(syn::Error::new(
ident.span(),
"#[pymethod] cannot define '__new__'. Use #[pyclass(with(Constructor))] instead.",
));
}
if py_name == "__init__" {
const FORBIDDEN_SLOT_METHODS: &[(&str, &str)] = &[
// Constructor/Initializer traits
("__new__", "Constructor"),
("__init__", "Initializer"),
// Representable trait
// ("__repr__", "Representable"),
// ("__str__", "???"), // allow __str__
// Hashable trait
("__hash__", "Hashable"),
// Callable trait
("__call__", "Callable"),
// GetAttr/SetAttr traits
// NOTE: __getattribute__, __setattr__, __delattr__ are intentionally NOT forbidden
// because they need pymethod for subclass override mechanism to work properly.
// GetDescriptor/SetDescriptor traits
// ("__get__", "GetDescriptor"),
// ("__set__", "SetDescriptor"),
// ("__delete__", "SetDescriptor"),
// AsNumber trait
("__add__", "AsNumber"),
("__radd__", "AsNumber"),
("__iadd__", "AsNumber"),
("__sub__", "AsNumber"),
("__rsub__", "AsNumber"),
("__isub__", "AsNumber"),
("__mul__", "AsNumber"),
("__rmul__", "AsNumber"),
("__imul__", "AsNumber"),
("__truediv__", "AsNumber"),
("__rtruediv__", "AsNumber"),
("__itruediv__", "AsNumber"),
("__floordiv__", "AsNumber"),
("__rfloordiv__", "AsNumber"),
("__ifloordiv__", "AsNumber"),
("__mod__", "AsNumber"),
("__rmod__", "AsNumber"),
("__imod__", "AsNumber"),
("__pow__", "AsNumber"),
("__rpow__", "AsNumber"),
("__ipow__", "AsNumber"),
("__divmod__", "AsNumber"),
("__rdivmod__", "AsNumber"),
("__matmul__", "AsNumber"),
("__rmatmul__", "AsNumber"),
("__imatmul__", "AsNumber"),
("__lshift__", "AsNumber"),
("__rlshift__", "AsNumber"),
("__ilshift__", "AsNumber"),
("__rshift__", "AsNumber"),
("__rrshift__", "AsNumber"),
("__irshift__", "AsNumber"),
("__and__", "AsNumber"),
("__rand__", "AsNumber"),
("__iand__", "AsNumber"),
("__or__", "AsNumber"),
("__ror__", "AsNumber"),
("__ior__", "AsNumber"),
("__xor__", "AsNumber"),
("__rxor__", "AsNumber"),
("__ixor__", "AsNumber"),
("__neg__", "AsNumber"),
("__pos__", "AsNumber"),
("__abs__", "AsNumber"),
("__invert__", "AsNumber"),
("__int__", "AsNumber"),
("__float__", "AsNumber"),
("__index__", "AsNumber"),
("__bool__", "AsNumber"),
// AsSequence trait
// ("__len__", "AsSequence (or AsMapping)"),
// ("__contains__", "AsSequence"),
// AsMapping trait
// ("__getitem__", "AsMapping (or AsSequence)"),
// ("__setitem__", "AsMapping (or AsSequence)"),
// ("__delitem__", "AsMapping (or AsSequence)"),
// IterNext trait
// ("__iter__", "IterNext"),
// ("__next__", "IterNext"),
// Comparable trait
("__eq__", "Comparable"),
("__ne__", "Comparable"),
("__lt__", "Comparable"),
("__le__", "Comparable"),
("__gt__", "Comparable"),
("__ge__", "Comparable"),
];

if let Some((_, trait_name)) = FORBIDDEN_SLOT_METHODS
.iter()
.find(|(method, _)| *method == py_name.as_str())
{
return Err(syn::Error::new(
ident.span(),
"#[pymethod] cannot define '__init__'. Use #[pyclass(with(Initializer))] instead.",
format!(
"#[pymethod] cannot define '{py_name}'. Use `impl {trait_name} for ...` instead. \
Slot methods are exposed as wrapper_descriptor automatically.",
),
));
}
}
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