IncorrectRaiseInSpecialMethod.ql

/**
 * @name Non-standard exception raised in special method
 * @description Raising a non-standard exception in a special method alters the expected interface of that method.
 * @kind problem
 * @tags reliability
 *       maintainability
 *       convention
 * @problem.severity recommendation
 * @sub-severity high
 * @precision very-high
 * @id py/unexpected-raise-in-special-method
 */

import python

private predicate attribute_method(string name) {
    name = "__getattribute__" or name = "__getattr__" or name = "__setattr__"
}

private predicate indexing_method(string name) {
    name = "__getitem__" or name = "__setitem__" or name = "__delitem__"
}

private predicate arithmetic_method(string name) {
    name = "__add__" or name = "__sub__" or name = "__div__" or
    name = "__pos__" or name = "__abs__" or name = "__floordiv__" or
    name = "__div__" or name = "__divmod__" or name = "__lshift__" or
    name = "__and__" or name = "__or__"or name = "__xor__" or name = "__rshift__" or
    name = "__pow__" or name = "__mul__" or name = "__neg__" or
    name = "__radd__" or name = "__rsub__" or name = "__rdiv__" or
    name = "__rfloordiv__" or name = "__rdiv__" or name = "__rlshift__" or
    name = "__rand__" or name = "__ror__"or name = "__rxor__" or name = "__rrshift__" or
    name = "__rpow__" or name = "__rmul__" or name = "__truediv__" or name = "__rtruediv__" or 
    name = "__iadd__" or name = "__isub__" or name = "__idiv__" or
    name = "__ifloordiv__" or name = "__idiv__" or name = "__ilshift__" or
    name = "__iand__" or name = "__ior__"or name = "__ixor__" or name = "__irshift__" or
    name = "__ipow__" or name = "__imul__" or name = "__itruediv__"
}

private predicate ordering_method(string name) {
    name = "__lt__" or name = "__le__" or name = "__gt__" or name = "__ge__" or 
    name = "__cmp__" and major_version() = 2
}

private predicate cast_method(string name) {
    name = "__nonzero__" and major_version() = 2 or 
    name = "__bool__"  or
    name = "__int__" or name = "__float__" or
    name = "__long__" or
    name = "__trunc__" or
    name = "__complex__"
}

predicate correct_raise(string name, ClassObject ex) {
    ex.getAnImproperSuperType() = theTypeErrorType()
    and
    (
      name = "__copy__" or
      name = "__deepcopy__" or
      name = "__call__" or
      indexing_method(name) or
      attribute_method(name)
    )
    or
    preferred_raise(name, ex)
    or
    preferred_raise(name, ex.getASuperType())
}

predicate preferred_raise(string name, ClassObject ex) {
    attribute_method(name) and ex = theAttributeErrorType()
    or
    indexing_method(name) and ex = builtin_object("LookupError")
    or
    ordering_method(name) and ex = theTypeErrorType()
    or
    arithmetic_method(name) and ex = builtin_object("ArithmeticError")
}

predicate no_need_to_raise(string name, string message) {
    name = "__hash__" and message = "use __hash__ = None instead"
    or
    cast_method(name) and message = "there is no need to implement the method at all."
}

predicate is_abstract(FunctionObject func) {
    ((Name)func.getFunction().getADecorator()).getId().matches("%abstract%")
}

predicate always_raises(FunctionObject f, ClassObject ex) {
    ex = f.getARaisedType() and 
    strictcount(f.getARaisedType()) = 1 and
    not exists(f.getFunction().getANormalExit()) and
    /* raising StopIteration is equivalent to a return in a generator */
    not ex = theStopIterationType()
}

from FunctionObject f, ClassObject cls, string message
where f.getFunction().isSpecialMethod() and 
not is_abstract(f) and
always_raises(f, cls) and
(
    no_need_to_raise(f.getName(), message) and not cls.getName() = "NotImplementedError" 
    or
    not correct_raise(f.getName(), cls) and not cls.getName() = "NotImplementedError" 
    and
    exists(ClassObject preferred | 
        preferred_raise(f.getName(), preferred) |
        message = "raise " + preferred.getName() + " instead"
    )
)
select f, "Function always raises $@; " + message, cls, cls.toString()