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73 lines
2.2 KiB
Plaintext
73 lines
2.2 KiB
Plaintext
/**
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* @name Unused loop iteration variable
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* @description A loop iteration variable is unused, which suggests an error.
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* @kind problem
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* @problem.severity error
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* @id js/unused-loop-variable
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* @tags maintainability
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* correctness
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* @precision high
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*/
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import javascript
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/**
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* An expression that adds a value to a variable.
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*
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* This includes `+=` expressions, pre- and post-increment expressions,
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* and expressions of the form `x = x + e`.
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*/
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class IncrementExpr extends Expr {
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IncrementExpr() {
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// x += e
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this instanceof AssignAddExpr
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or
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// ++x or x++
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this instanceof PreIncExpr
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or
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this instanceof PostIncExpr
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or
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// x = x + e
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exists(AssignExpr assgn, Variable v | assgn = this |
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assgn.getTarget() = v.getAnAccess() and
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assgn.getRhs().(AddExpr).getAnOperand().getUnderlyingReference() = v.getAnAccess()
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)
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}
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}
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/**
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* Holds if `efl` is a loop whose body increments a variable and does nothing else.
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*/
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predicate countingLoop(EnhancedForLoop efl) {
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exists(ExprStmt inc | inc.getExpr().stripParens() instanceof IncrementExpr |
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inc = efl.getBody() or
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inc = efl.getBody().(BlockStmt).getAStmt()
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)
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}
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/**
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* Holds if `iter` is a non-last variable of array-destructuring in a for-loop.
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* For example `foo` or `iter` in `for(const [foo, iter, bar] of array) {..}`.
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*/
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predicate isNonLastDestructedArrayElement(PurelyLocalVariable iter) {
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exists(ArrayPattern pattern | pattern = any(EnhancedForLoop loop).getLValue() |
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iter = pattern.getAVariable() and
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iter =
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pattern
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.getElement([0 .. pattern.getSize() - 2])
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.(BindingPattern)
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.getABindingVarRef()
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.getVariable()
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)
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}
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from EnhancedForLoop efl, PurelyLocalVariable iter
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where
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iter = efl.getAnIterationVariable() and
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not exists(SsaExplicitDefinition ssa | ssa.defines(efl.getIteratorExpr(), iter)) and
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exists(ReachableBasicBlock body | body.getANode() = efl.getBody() | body.getASuccessor+() = body) and
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not countingLoop(efl) and
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not isNonLastDestructedArrayElement(iter) and
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not iter.getName().toLowerCase().regexpMatch("(_|dummy|unused).*")
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select efl.getIterator(), "For loop variable " + iter.getName() + " is not used in the loop body."
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