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Rosanny Sihombing authoredcea2f272
/** * @fileoverview Rule to disallow loops with a body that allows only one iteration * @author Milos Djermanovic */"use strict";//------------------------------------------------------------------------------// Helpers//------------------------------------------------------------------------------const allLoopTypes = ["WhileStatement", "DoWhileStatement", "ForStatement", "ForInStatement", "ForOfStatement"];/** * Determines whether the given node is the first node in the code path to which a loop statement * 'loops' for the next iteration. * @param {ASTNode} node The node to check. * @returns {boolean} `true` if the node is a looping target. */function isLoopingTarget(node) { const parent = node.parent; if (parent) { switch (parent.type) { case "WhileStatement": return node === parent.test; case "DoWhileStatement": return node === parent.body; case "ForStatement": return node === (parent.update || parent.test || parent.body); case "ForInStatement": case "ForOfStatement": return node === parent.left; // no default } } return false;}/** * Creates an array with elements from the first given array that are not included in the second given array. * @param {Array} arrA The array to compare from. * @param {Array} arrB The array to compare against. * @returns {Array} a new array that represents `arrA \ arrB`. */function getDifference(arrA, arrB) { return arrA.filter(a => !arrB.includes(a));}//------------------------------------------------------------------------------// Rule Definition//------------------------------------------------------------------------------module.exports = { meta: { type: "problem", docs: { description: "disallow loops with a body that allows only one iteration", category: "Possible Errors", recommended: false, url: "https://eslint.org/docs/rules/no-unreachable-loop" }, schema: [{ type: "object", properties: { ignore: {
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type: "array",
items: {
enum: allLoopTypes
},
uniqueItems: true
}
},
additionalProperties: false
}],
messages: {
invalid: "Invalid loop. Its body allows only one iteration."
}
},
create(context) {
const ignoredLoopTypes = context.options[0] && context.options[0].ignore || [],
loopTypesToCheck = getDifference(allLoopTypes, ignoredLoopTypes),
loopSelector = loopTypesToCheck.join(","),
loopsByTargetSegments = new Map(),
loopsToReport = new Set();
let currentCodePath = null;
return {
onCodePathStart(codePath) {
currentCodePath = codePath;
},
onCodePathEnd() {
currentCodePath = currentCodePath.upper;
},
[loopSelector](node) {
/**
* Ignore unreachable loop statements to avoid unnecessary complexity in the implementation, or false positives otherwise.
* For unreachable segments, the code path analysis does not raise events required for this implementation.
*/
if (currentCodePath.currentSegments.some(segment => segment.reachable)) {
loopsToReport.add(node);
}
},
onCodePathSegmentStart(segment, node) {
if (isLoopingTarget(node)) {
const loop = node.parent;
loopsByTargetSegments.set(segment, loop);
}
},
onCodePathSegmentLoop(_, toSegment, node) {
const loop = loopsByTargetSegments.get(toSegment);
/**
* The second iteration is reachable, meaning that the loop is valid by the logic of this rule,
* only if there is at least one loop event with the appropriate target (which has been already
* determined in the `loopsByTargetSegments` map), raised from either:
*
* - the end of the loop's body (in which case `node === loop`)
* - a `continue` statement
*
* This condition skips loop events raised from `ForInStatement > .right` and `ForOfStatement > .right` nodes.
*/
if (node === loop || node.type === "ContinueStatement") {
// Removes loop if it exists in the set. Otherwise, `Set#delete` has no effect and doesn't throw.
loopsToReport.delete(loop);
}