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LoopVariableCapture.ql

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/**

* @name Loop variable capture

* @description Capture of a loop variable is not the same as capturing the value of a loop variable, and may be erroneous.

* @kind problem

* @tags correctness

* @problem.severity error

* @sub-severity low

* @precision high

* @id py/loop-variable-capture

*/

import python

// Gets the scope of the iteration variable of the looping scope

Scope iteration_variable_scope(AstNode loop) {

result = loop.(For).getScope()

or

result = loop.(Comp).getFunction()

}

predicate capturing_looping_construct(CallableExpr capturing, AstNode loop, Variable var) {

var.getScope() = iteration_variable_scope(loop) and

var.getAnAccess().getScope() = capturing.getInnerScope() and

capturing.getParentNode+() = loop and

(

loop.(For).getTarget() = var.getAnAccess()

or

var = loop.(Comp).getAnIterationVariable()

)

}

predicate escaping_capturing_looping_construct(CallableExpr capturing, AstNode loop, Variable var) {

capturing_looping_construct(capturing, loop, var) and

// Escapes if used out side of for loop or is a lambda in a comprehension

(

loop instanceof For and

exists(Expr e | e.pointsTo(_, _, capturing) | not loop.contains(e))

or

loop.(Comp).getElt() = capturing

or

loop.(Comp).getElt().(Tuple).getAnElt() = capturing

)

}

from CallableExpr capturing, AstNode loop, Variable var

where escaping_capturing_looping_construct(capturing, loop, var)

select capturing, "Capture of loop variable $@.", loop, var.getId()