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