UnnecessaryLambda.ql

/**
 * @name Unnecessary lambda
 * @description A lambda is used that calls through to a function without modifying any parameters
 * @kind problem
 * @tags maintainability
 *       useless-code
 * @problem.severity recommendation
 * @sub-severity high
 * @precision high
 * @id py/unnecessary-lambda
 */

import python

/* f consists of a single return statement, whose value is a call. The arguments of the call are exactly the parameters of f */
predicate simple_wrapper(Lambda l, Expr wrapped) {
    exists(Function f, Call c | f = l.getInnerScope() and c = l.getExpression() |
           wrapped = c.getFunc() and
           count(f.getAnArg()) = count(c.getAnArg()) and
           forall(int arg | exists(f.getArg(arg)) |
                  f.getArgName(arg) = ((Name)c.getArg(arg)).getId()) and
            /* Either no **kwargs or they must match */
           (not exists(f.getKwarg()) and not exists(c.getKwargs()) or
            ((Name)f.getKwarg()).getId() = ((Name)c.getKwargs()).getId()) and
           /* Either no *args or they must match */
           (not exists(f.getVararg()) and not exists(c.getStarargs()) or
            ((Name)f.getVararg()).getId() = ((Name)c.getStarargs()).getId()) and
            /* No named parameters in call */
            not exists(c.getAKeyword())
    )
    and
    // f is not necessarily a drop-in replacement for the lambda if there are default argument values
    not exists(l.getArgs().getADefault())
}

/* The expression called will refer to the same object if evaluated when the lambda is created or when the lambda is executed. */
predicate unnecessary_lambda(Lambda l, Expr e) {
    simple_wrapper(l, e) and 
    (
      /* plain class */
      exists(ClassObject c | e.refersTo(c))
      or
      /* plain function */
      exists(FunctionObject f | e.refersTo(f))
      or
      /* bound-method of enclosing instance */
      exists(ClassObject cls, Attribute a | 
          cls.getPyClass() = l.getScope().getScope() and a = e |
          ((Name)a.getObject()).getId() = "self" and
          cls.hasAttribute(a.getName())
      )
    )
}

from Lambda l, Expr e
where unnecessary_lambda(l, e)
select l,  "This 'lambda' is just a simple wrapper around a callable object. Use that object directly."