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/**

* @name Self assignment

* @description Assigning a variable to itself has no effect.

* @kind problem

* @problem.severity warning

* @id js/redundant-assignment

* @tags quality

* reliability

* correctness

* external/cwe/cwe-480

* external/cwe/cwe-561

* @precision high

*/

import Clones

import Expressions.DOMProperties

/**

* Gets a description of expression `e`, which is assumed to be the left-hand

* side of an assignment.

*

* For variable accesses, the description is the variable name. For property

* accesses, the description is of the form `"property <name>"`, where

* `<name>` is the name of the property, except if `<name>` is a numeric index,

* in which case `element <name>` is used instead.

*/

string describe(Expr e) {

exists(VarAccess va | va = e | result = "variable " + va.getName())

or

exists(string name | name = e.(PropAccess).getPropertyName() |

if exists(name.toInt()) then result = "element " + name else result = "property " + name

)

}

from SelfAssignment e, string dsc

where

e.same(_) and

dsc = describe(e) and

// exclude properties for which there is an accessor somewhere

not exists(string propName | propName = e.(PropAccess).getPropertyName() |

propName = any(PropertyAccessor acc).getName() or

propName = any(AccessorMethodDeclaration amd).getName()

) and

// exclude DOM properties

not isDomProperty(e.(PropAccess).getPropertyName()) and

// exclude self-assignments that have been inserted to satisfy the TypeScript JS-checker

not e.getAssignment().getParent().(ExprStmt).getDocumentation().getATag().getTitle() = "type" and

// exclude self-assignments in speculatively parsed template files

// named arguments may be incorrectly parsed as assignments

not e.getTopLevel() instanceof Templating::TemplateTopLevel

select e.getParent(), "This expression assigns " + dsc + " to itself."