126 lines
4.3 KiB
JavaScript
126 lines
4.3 KiB
JavaScript
/**
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* @fileoverview enforce "for" loop update clause moving the counter in the right direction.(for-direction)
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* @author Aladdin-ADD<hh_2013@foxmail.com>
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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type: "problem",
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docs: {
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description: "enforce \"for\" loop update clause moving the counter in the right direction.",
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category: "Possible Errors",
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recommended: true,
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url: "https://eslint.org/docs/rules/for-direction"
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},
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fixable: null,
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schema: [],
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messages: {
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incorrectDirection: "The update clause in this loop moves the variable in the wrong direction."
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}
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},
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create(context) {
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/**
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* report an error.
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* @param {ASTNode} node the node to report.
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* @returns {void}
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*/
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function report(node) {
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context.report({
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node,
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messageId: "incorrectDirection"
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});
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}
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/**
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* check the right side of the assignment
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* @param {ASTNode} update UpdateExpression to check
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* @param {int} dir expected direction that could either be turned around or invalidated
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* @returns {int} return dir, the negated dir or zero if it's not clear for identifiers
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*/
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function getRightDirection(update, dir) {
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if (update.right.type === "UnaryExpression") {
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if (update.right.operator === "-") {
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return -dir;
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}
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} else if (update.right.type === "Identifier") {
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return 0;
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}
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return dir;
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}
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/**
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* check UpdateExpression add/sub the counter
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* @param {ASTNode} update UpdateExpression to check
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* @param {string} counter variable name to check
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* @returns {int} if add return 1, if sub return -1, if nochange, return 0
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*/
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function getUpdateDirection(update, counter) {
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if (update.argument.type === "Identifier" && update.argument.name === counter) {
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if (update.operator === "++") {
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return 1;
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}
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if (update.operator === "--") {
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return -1;
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}
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}
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return 0;
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}
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/**
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* check AssignmentExpression add/sub the counter
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* @param {ASTNode} update AssignmentExpression to check
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* @param {string} counter variable name to check
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* @returns {int} if add return 1, if sub return -1, if nochange, return 0
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*/
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function getAssignmentDirection(update, counter) {
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if (update.left.name === counter) {
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if (update.operator === "+=") {
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return getRightDirection(update, 1);
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}
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if (update.operator === "-=") {
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return getRightDirection(update, -1);
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}
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}
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return 0;
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}
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return {
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ForStatement(node) {
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if (node.test && node.test.type === "BinaryExpression" && node.test.left.type === "Identifier" && node.update) {
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const counter = node.test.left.name;
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const operator = node.test.operator;
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const update = node.update;
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let wrongDirection;
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if (operator === "<" || operator === "<=") {
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wrongDirection = -1;
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} else if (operator === ">" || operator === ">=") {
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wrongDirection = 1;
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} else {
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return;
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}
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if (update.type === "UpdateExpression") {
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if (getUpdateDirection(update, counter) === wrongDirection) {
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report(node);
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}
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} else if (update.type === "AssignmentExpression" && getAssignmentDirection(update, counter) === wrongDirection) {
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report(node);
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}
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}
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}
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};
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}
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};
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