318 lines
12 KiB
JavaScript
318 lines
12 KiB
JavaScript
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/**
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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("./utils/ast-utils");
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const eslintUtils = require("eslint-utils");
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const precedence = astUtils.getPrecedence;
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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/** @type {import('../shared/types').Rule} */
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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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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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type: "object",
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properties: {
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enforceForLogicalOperands: {
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type: "boolean",
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default: false
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}
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},
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additionalProperties: false
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}],
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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 = new Set([
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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 a Boolean function or constructor.
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* @param {ASTNode} node the node
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* @returns {boolean} If the node is Boolean function or constructor
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*/
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function isBooleanFunctionOrConstructorCall(node) {
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// Boolean(<bool>) and new Boolean(<bool>)
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return (node.type === "CallExpression" || node.type === "NewExpression") &&
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node.callee.type === "Identifier" &&
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node.callee.name === "Boolean";
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}
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/**
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* Checks whether the node is a logical expression and that the option is enabled
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* @param {ASTNode} node the node
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* @returns {boolean} if the node is a logical expression and option is enabled
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*/
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function isLogicalContext(node) {
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return node.type === "LogicalExpression" &&
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(node.operator === "||" || node.operator === "&&") &&
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(context.options.length && context.options[0].enforceForLogicalOperands === true);
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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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* @param {ASTNode} node The node
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* @returns {boolean} If it is in a boolean context
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*/
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function isInBooleanContext(node) {
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return (
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(isBooleanFunctionOrConstructorCall(node.parent) &&
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node === node.parent.arguments[0]) ||
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(BOOLEAN_NODE_TYPES.has(node.parent.type) &&
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node === node.parent.test) ||
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// !<bool>
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(node.parent.type === "UnaryExpression" &&
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node.parent.operator === "!")
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);
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}
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/**
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* Checks whether the node is a context that should report an error
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* Acts recursively if it is in a logical context
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* @param {ASTNode} node the node
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* @returns {boolean} If the node is in one of the flagged contexts
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*/
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function isInFlaggedContext(node) {
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if (node.parent.type === "ChainExpression") {
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return isInFlaggedContext(node.parent);
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}
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return isInBooleanContext(node) ||
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(isLogicalContext(node.parent) &&
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// For nested logical statements
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isInFlaggedContext(node.parent)
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);
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}
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/**
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* Check if a node has comments inside.
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* @param {ASTNode} node The node to check.
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* @returns {boolean} `true` if it has comments inside.
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*/
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function hasCommentsInside(node) {
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return Boolean(sourceCode.getCommentsInside(node).length);
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}
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/**
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* Checks if the given node is wrapped in grouping parentheses. Parentheses for constructs such as if() don't count.
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* @param {ASTNode} node The node to check.
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* @returns {boolean} `true` if the node is parenthesized.
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* @private
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*/
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function isParenthesized(node) {
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return eslintUtils.isParenthesized(1, node, sourceCode);
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}
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/**
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* Determines whether the given node needs to be parenthesized when replacing the previous node.
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* It assumes that `previousNode` is the node to be reported by this rule, so it has a limited list
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* of possible parent node types. By the same assumption, the node's role in a particular parent is already known.
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* For example, if the parent is `ConditionalExpression`, `previousNode` must be its `test` child.
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* @param {ASTNode} previousNode Previous node.
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* @param {ASTNode} node The node to check.
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* @throws {Error} (Unreachable.)
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* @returns {boolean} `true` if the node needs to be parenthesized.
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*/
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function needsParens(previousNode, node) {
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if (previousNode.parent.type === "ChainExpression") {
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return needsParens(previousNode.parent, node);
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}
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if (isParenthesized(previousNode)) {
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// parentheses around the previous node will stay, so there is no need for an additional pair
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return false;
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}
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// parent of the previous node will become parent of the replacement node
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const parent = previousNode.parent;
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switch (parent.type) {
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case "CallExpression":
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case "NewExpression":
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return node.type === "SequenceExpression";
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case "IfStatement":
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case "DoWhileStatement":
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case "WhileStatement":
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case "ForStatement":
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return false;
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case "ConditionalExpression":
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return precedence(node) <= precedence(parent);
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case "UnaryExpression":
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return precedence(node) < precedence(parent);
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case "LogicalExpression":
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if (astUtils.isMixedLogicalAndCoalesceExpressions(node, parent)) {
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return true;
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}
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if (previousNode === parent.left) {
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return precedence(node) < precedence(parent);
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}
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return precedence(node) <= precedence(parent);
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/* istanbul ignore next */
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default:
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throw new Error(`Unexpected parent type: ${parent.type}`);
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}
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}
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return {
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UnaryExpression(node) {
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const parent = node.parent;
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// Exit early if it's guaranteed not to match
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if (node.operator !== "!" ||
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parent.type !== "UnaryExpression" ||
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parent.operator !== "!") {
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return;
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}
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if (isInFlaggedContext(parent)) {
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context.report({
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node: parent,
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messageId: "unexpectedNegation",
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fix(fixer) {
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if (hasCommentsInside(parent)) {
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return null;
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}
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if (needsParens(parent, node.argument)) {
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return fixer.replaceText(parent, `(${sourceCode.getText(node.argument)})`);
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}
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let prefix = "";
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const tokenBefore = sourceCode.getTokenBefore(parent);
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const firstReplacementToken = sourceCode.getFirstToken(node.argument);
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if (
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tokenBefore &&
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tokenBefore.range[1] === parent.range[0] &&
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!astUtils.canTokensBeAdjacent(tokenBefore, firstReplacementToken)
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) {
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prefix = " ";
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}
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return fixer.replaceText(parent, prefix + sourceCode.getText(node.argument));
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}
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});
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}
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},
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CallExpression(node) {
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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 (isInFlaggedContext(node)) {
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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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const parent = node.parent;
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if (node.arguments.length === 0) {
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if (parent.type === "UnaryExpression" && parent.operator === "!") {
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/*
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* !Boolean() -> true
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*/
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if (hasCommentsInside(parent)) {
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return null;
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}
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const replacement = "true";
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let prefix = "";
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const tokenBefore = sourceCode.getTokenBefore(parent);
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if (
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tokenBefore &&
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tokenBefore.range[1] === parent.range[0] &&
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!astUtils.canTokensBeAdjacent(tokenBefore, replacement)
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) {
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prefix = " ";
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}
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return fixer.replaceText(parent, prefix + replacement);
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}
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/*
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* Boolean() -> false
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*/
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if (hasCommentsInside(node)) {
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return null;
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}
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return fixer.replaceText(node, "false");
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}
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if (node.arguments.length === 1) {
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const argument = node.arguments[0];
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if (argument.type === "SpreadElement" || hasCommentsInside(node)) {
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return null;
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}
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/*
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* Boolean(expression) -> expression
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*/
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if (needsParens(node, argument)) {
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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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// two or more arguments
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return null;
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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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