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Esben Sparre Andreasen
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JS: add query js/unused-property
1 parent 0cf2eae commit 91dccc3

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Lines changed: 301 additions & 51 deletions

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‎javascript/config/suites/javascript/maintainability-more‎

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+ semmlecode-javascript-queries/Declarations/DeadStoreOfProperty.ql: /Maintainability/Declarations
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+ semmlecode-javascript-queries/Declarations/DuplicateVarDecl.ql: /Maintainability/Declarations
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+ semmlecode-javascript-queries/Declarations/UnusedParameter.ql: /Maintainability/Declarations
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+ semmlecode-javascript-queries/Declarations/UnusedProperty.ql: /Maintainability/Declarations
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+ semmlecode-javascript-queries/Declarations/UnusedVariable.ql: /Maintainability/Declarations
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+ semmlecode-javascript-queries/Expressions/UnneededDefensiveProgramming.ql: /Maintainability/Expressions
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+ semmlecode-javascript-queries/LanguageFeatures/ArgumentsCallerCallee.ql: /Maintainability/Language Features

‎javascript/ql/src/Declarations/UnusedProperty.qhelp‎

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>
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Unused object properties make code harder to maintain and use. Clients that are unaware that a
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property is unused may perform nontrivial computations to compute a value that is ultimately
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unused.
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</p>
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</overview>
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<recommendation>
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<p>Remove the unused property.</p>
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</recommendation>
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<example>
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<p>
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In this code, the function <code>f</code> initializes a property <code>prop_a</code> with a
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call to the function <code>expensiveComputation</code>, but later on this property is never read.
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Removing <code>prop</code> would improve code quality and performance.
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</p>
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<sample src="examples/UnusedProperty.js" />
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</example>
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<references>
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<li>Coding Horror: <a href="http://blog.codinghorror.com/code-smells/">Code Smells</a>.</li>
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</references>
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</qhelp>

‎javascript/ql/src/Declarations/UnusedProperty.ql‎

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/**
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* @name Unused property
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* @description Unused properties may be a symptom of a bug and should be examined carefully.
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* @kind problem
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* @problem.severity recommendation
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* @id js/unused-property
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* @tags maintainability
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* @precision high
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*/
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import javascript
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import semmle.javascript.dataflow.CapturedNodes
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import UnusedVariable
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import UnusedParameter
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import Expressions.ExprHasNoEffect
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predicate hasUnknownPropertyRead(CapturedSource obj) {
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// dynamic reads
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exists(DataFlow::PropRead r | obj.getAPropertyRead() = r | not exists(r.getPropertyName()))
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or
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// reflective reads
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obj.flowsToExpr(any(EnhancedForLoop l).getIterationDomain())
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or
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obj.flowsToExpr(any(InExpr l).getRightOperand())
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or
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obj.flowsToExpr(any(SpreadElement e).getOperand())
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or
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exists(obj.getAPropertyRead("hasOwnProperty"))
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or
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exists(obj.getAPropertyRead("propertyIsEnumerable"))
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}
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predicate flowsToTypeRestrictedExpression(CapturedSource n) {
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exists (Expr restricted, TypeExpr type |
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n.flowsToExpr(restricted) and
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not type.isAny() |
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exists (TypeAssertion assertion |
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type = assertion.getTypeAnnotation() and
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restricted = assertion.getExpression()
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)
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or
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exists (BindingPattern v |
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type = v.getTypeAnnotation() and
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restricted = v.getAVariable().getAnAssignedExpr()
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)
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// no need to reason about writes to typed fields, captured nodes do not reach them
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)
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}
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from DataFlow::PropWrite w, CapturedSource n, string name
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where
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w = n.getAPropertyWrite(name) and
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not exists(n.getAPropertyRead(name)) and
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not w.getBase().analyze().getAValue() != n.analyze().getAValue() and
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not hasUnknownPropertyRead(n) and
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// avoid reporting if the definition is unreachable
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w.getAstNode().getFirstControlFlowNode().getBasicBlock() instanceof ReachableBasicBlock and
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// avoid implicitly read properties
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not (
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name = "toString" or
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name = "valueOf" or
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name.matches("@@%") // @@iterator, for example
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) and
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// avoid flagging properties that a type system requires
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not flowsToTypeRestrictedExpression(n) and
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// flagged by js/unused-local-variable
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not exists(UnusedLocal l | l.getAnAssignedExpr().getUnderlyingValue().flow() = n) and
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// flagged by js/unused-parameter
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not exists(Parameter p | isAnAccidentallyUnusedParameter(p) |
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p.getDefault().getUnderlyingValue().flow() = n
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) and
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// flagged by js/useless-expression
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not inVoidContext(n.asExpr())
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select w, "Unused property " + name + "."

‎javascript/ql/src/Declarations/UnusedVariable.ql‎

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*/
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import javascript
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/**
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* A local variable that is neither used nor exported, and is not a parameter
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* or a function name.
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*/
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class UnusedLocal extends LocalVariable {
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UnusedLocal() {
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not exists(getAnAccess()) and
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not exists(Parameter p | this = p.getAVariable()) and
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not exists(FunctionExpr fe | this = fe.getVariable()) and
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not exists(ClassExpr ce | this = ce.getVariable()) and
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not exists(ExportDeclaration ed | ed.exportsAs(this, _)) and
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not exists(LocalVarTypeAccess type | type.getVariable() = this) and
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// common convention: variables with leading underscore are intentionally unused
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getName().charAt(0) != "_"
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}
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}
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import UnusedVariable
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/**
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* Holds if `v` is mentioned in a JSDoc comment in the same file, and that file

‎javascript/ql/src/Declarations/UnusedVariable.qll‎

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/**
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* This library contains parts of the 'js/unused-local-variable' query implementation.
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*/
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import javascript
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/**
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* A local variable that is neither used nor exported, and is not a parameter
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* or a function name.
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*/
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class UnusedLocal extends LocalVariable {
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UnusedLocal() {
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not exists(getAnAccess()) and
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not exists(Parameter p | this = p.getAVariable()) and
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not exists(FunctionExpr fe | this = fe.getVariable()) and
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not exists(ClassExpr ce | this = ce.getVariable()) and
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not exists(ExportDeclaration ed | ed.exportsAs(this, _)) and
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not exists(LocalVarTypeAccess type | type.getVariable() = this) and
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// common convention: variables with leading underscore are intentionally unused
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getName().charAt(0) != "_"
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}
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}

‎javascript/ql/src/Declarations/examples/UnusedProperty.js‎

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function f() {
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var o = {
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prop_a: expensiveComputation(),
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prop_b: anotherComputation()
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};
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return o.prop_b;
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}

‎javascript/ql/src/Expressions/ExprHasNoEffect.ql‎

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import DOMProperties
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import semmle.javascript.frameworks.xUnit
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import semmle.javascript.RestrictedLocations
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/**
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* Holds if `e` appears in a syntactic context where its value is discarded.
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*/
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predicate inVoidContext(Expr e) {
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exists(ExprStmt parent |
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// e is a toplevel expression in an expression statement
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parent = e.getParent() and
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// but it isn't an HTML attribute or a configuration object
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not exists(TopLevel tl | tl = parent.getParent() |
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tl instanceof CodeInAttribute
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or
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// if the toplevel in its entirety is of the form `({ ... })`,
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// it is probably a configuration object (e.g., a require.js build configuration)
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tl.getNumChildStmt() = 1 and e.stripParens() instanceof ObjectExpr
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)
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)
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or
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exists(SeqExpr seq, int i, int n |
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e = seq.getOperand(i) and
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n = seq.getNumOperands()
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|
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i < n - 1 or inVoidContext(seq)
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)
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or
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exists(ForStmt stmt | e = stmt.getUpdate())
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or
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exists(ForStmt stmt | e = stmt.getInit() |
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// Allow the pattern `for(i; i < 10; i++)`
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not e instanceof VarAccess
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)
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or
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exists(LogicalBinaryExpr logical | e = logical.getRightOperand() and inVoidContext(logical))
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}
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import ExprHasNoEffect
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/**
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* Holds if `e` is of the form `x;` or `e.p;` and has a JSDoc comment containing a tag.

‎javascript/ql/src/Expressions/ExprHasNoEffect.qll‎

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/**
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* This library contains parts of the 'js/useless-expression' query implementation.
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*/
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import javascript
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/**
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* Holds if `e` appears in a syntactic context where its value is discarded.
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*/
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predicate inVoidContext(Expr e) {
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exists(ExprStmt parent |
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// e is a toplevel expression in an expression statement
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parent = e.getParent() and
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// but it isn't an HTML attribute or a configuration object
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not exists(TopLevel tl | tl = parent.getParent() |
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tl instanceof CodeInAttribute
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or
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// if the toplevel in its entirety is of the form `({ ... })`,
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// it is probably a configuration object (e.g., a require.js build configuration)
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tl.getNumChildStmt() = 1 and e.stripParens() instanceof ObjectExpr
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)
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)
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or
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exists(SeqExpr seq, int i, int n |
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e = seq.getOperand(i) and
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n = seq.getNumOperands()
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|
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i < n - 1 or inVoidContext(seq)
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)
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or
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exists(ForStmt stmt | e = stmt.getUpdate())
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or
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exists(ForStmt stmt | e = stmt.getInit() |
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// Allow the pattern `for(i; i < 10; i++)`
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not e instanceof VarAccess
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)
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or
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exists(LogicalBinaryExpr logical | e = logical.getRightOperand() and inVoidContext(logical))
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}

‎javascript/ql/test/query-tests/Declarations/UnusedProperty/UnusedProperty.expected‎

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| tst.js:4:9:4:19 | unused1: 42 | Unused property unused1. |
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| tst.js:19:5:19:15 | unused9: 42 | Unused property unused9. |
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| tst.js:26:13:26:24 | unused11: 42 | Unused property unused11. |
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| tst.js:31:13:31:35 | used12_ ... lly: 42 | Unused property used12_butNotReally. |
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| tst.js:32:13:32:24 | unused12: 42 | Unused property unused12. |
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| tst.js:52:3:52:14 | unused14: 42 | Unused property unused14. |
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| tst.js:54:2:54:20 | captured14.unused14 | Unused property unused14. |
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| tst.js:55:2:55:20 | captured14.unused14 | Unused property unused14. |
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| tst.ts:24:21:24:25 | p: 42 | Unused property p. |

‎javascript/ql/test/query-tests/Declarations/UnusedProperty/UnusedProperty.qlref‎

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Declarations/UnusedProperty.ql

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