/**
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* @fileoverview Rule to flag unnecessary double negation in Boolean contexts
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* @author Brandon Mills
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Requirements
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//------------------------------------------------------------------------------
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const astUtils = require("../util/ast-utils");
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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: "suggestion",
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docs: {
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description: "disallow unnecessary boolean casts",
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category: "Possible Errors",
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recommended: true,
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url: "https://eslint.org/docs/rules/no-extra-boolean-cast"
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},
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schema: [],
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fixable: "code",
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messages: {
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unexpectedCall: "Redundant Boolean call.",
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unexpectedNegation: "Redundant double negation."
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}
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},
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create(context) {
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const sourceCode = context.getSourceCode();
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// Node types which have a test which will coerce values to booleans.
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const BOOLEAN_NODE_TYPES = [
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"IfStatement",
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"DoWhileStatement",
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"WhileStatement",
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"ConditionalExpression",
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"ForStatement"
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];
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/**
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* Check if a node is in a context where its value would be coerced to a boolean at runtime.
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*
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* @param {Object} node The node
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* @param {Object} parent Its parent
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* @returns {boolean} If it is in a boolean context
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*/
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function isInBooleanContext(node, parent) {
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return (
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(BOOLEAN_NODE_TYPES.indexOf(parent.type) !== -1 &&
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node === parent.test) ||
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// !<bool>
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(parent.type === "UnaryExpression" &&
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parent.operator === "!")
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);
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}
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return {
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UnaryExpression(node) {
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const ancestors = context.getAncestors(),
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parent = ancestors.pop(),
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grandparent = ancestors.pop();
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// Exit early if it's guaranteed not to match
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if (node.operator !== "!" ||
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parent.type !== "UnaryExpression" ||
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parent.operator !== "!") {
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return;
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}
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if (isInBooleanContext(parent, grandparent) ||
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// Boolean(<bool>) and new Boolean(<bool>)
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((grandparent.type === "CallExpression" || grandparent.type === "NewExpression") &&
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grandparent.callee.type === "Identifier" &&
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grandparent.callee.name === "Boolean")
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) {
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context.report({
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node,
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messageId: "unexpectedNegation",
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fix: fixer => fixer.replaceText(parent, sourceCode.getText(node.argument))
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});
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}
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},
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CallExpression(node) {
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const parent = node.parent;
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if (node.callee.type !== "Identifier" || node.callee.name !== "Boolean") {
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return;
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}
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if (isInBooleanContext(node, parent)) {
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context.report({
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node,
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messageId: "unexpectedCall",
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fix: fixer => {
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if (!node.arguments.length) {
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return fixer.replaceText(parent, "true");
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}
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if (node.arguments.length > 1 || node.arguments[0].type === "SpreadElement") {
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return null;
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}
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const argument = node.arguments[0];
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if (astUtils.getPrecedence(argument) < astUtils.getPrecedence(node.parent)) {
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return fixer.replaceText(node, `(${sourceCode.getText(argument)})`);
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}
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return fixer.replaceText(node, sourceCode.getText(argument));
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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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};
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