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/**

* @name Variable defined multiple times

* @description Assignment to a variable occurs multiple times without any intermediate use of that variable

* @kind problem

* @tags maintainability

* useless-code

* external/cwe/cwe-563

* @problem.severity warning

* @sub-severity low

* @precision very-high

* @id py/multiple-definition

*/

import python

import Definition

predicate multiply_defined(AstNode asgn1, AstNode asgn2, Variable v) {

/*

* Must be redefined on all possible paths in the CFG corresponding to the original source.

* For example, splitting may create a path where `def` is unconditionally redefined, even though

* it is not in the original source.

*/

forex(Definition def, Definition redef |

def.getVariable() = v and

def = asgn1.getAFlowNode() and

redef = asgn2.getAFlowNode()

|

def.isUnused() and

def.getARedef() = redef and

def.isRelevant()

)

}

predicate simple_literal(Expr e) {

e.(Num).getN() = "0"

or

e instanceof NameConstant

or

e instanceof List and not exists(e.(List).getAnElt())

or

e instanceof Tuple and not exists(e.(Tuple).getAnElt())

or

e instanceof Dict and not exists(e.(Dict).getAKey())

or

e.(StrConst).getText() = ""

}

/**

* A multiple definition is 'uninteresting' if it sets a variable to a

* simple literal before reassigning it.

* x = None

* if cond:

* x = value1

* else:

* x = value2

*/

predicate uninteresting_definition(AstNode asgn1) {

exists(AssignStmt a | a.getATarget() = asgn1 | simple_literal(a.getValue()))

}

from AstNode asgn1, AstNode asgn2, Variable v

where

multiply_defined(asgn1, asgn2, v) and

forall(Name el | el = asgn1.getParentNode().(Tuple).getAnElt() | multiply_defined(el, _, _)) and

not uninteresting_definition(asgn1)

select asgn1,

"This assignment to '" + v.getId() +

"' is unnecessary as it is redefined $@ before this value is used.", asgn2 as t, "here"