/** * @fileoverview Disallow parenthesising higher precedence subexpressions. * @author Michael Ficarra */ "use strict"; //------------------------------------------------------------------------------ // Rule Definition //------------------------------------------------------------------------------ const astUtils = require("./utils/ast-utils.js"); module.exports = { meta: { type: "layout", docs: { description: "disallow unnecessary parentheses", category: "Possible Errors", recommended: false, url: "https://eslint.org/docs/rules/no-extra-parens" }, fixable: "code", schema: { anyOf: [ { type: "array", items: [ { enum: ["functions"] } ], minItems: 0, maxItems: 1 }, { type: "array", items: [ { enum: ["all"] }, { type: "object", properties: { conditionalAssign: { type: "boolean" }, nestedBinaryExpressions: { type: "boolean" }, returnAssign: { type: "boolean" }, ignoreJSX: { enum: ["none", "all", "single-line", "multi-line"] }, enforceForArrowConditionals: { type: "boolean" } }, additionalProperties: false } ], minItems: 0, maxItems: 2 } ] }, messages: { unexpected: "Unnecessary parentheses around expression." } }, create(context) { const sourceCode = context.getSourceCode(); const tokensToIgnore = new WeakSet(); const isParenthesised = astUtils.isParenthesised.bind(astUtils, sourceCode); const precedence = astUtils.getPrecedence; const ALL_NODES = context.options[0] !== "functions"; const EXCEPT_COND_ASSIGN = ALL_NODES && context.options[1] && context.options[1].conditionalAssign === false; const NESTED_BINARY = ALL_NODES && context.options[1] && context.options[1].nestedBinaryExpressions === false; const EXCEPT_RETURN_ASSIGN = ALL_NODES && context.options[1] && context.options[1].returnAssign === false; const IGNORE_JSX = ALL_NODES && context.options[1] && context.options[1].ignoreJSX; const IGNORE_ARROW_CONDITIONALS = ALL_NODES && context.options[1] && context.options[1].enforceForArrowConditionals === false; const PRECEDENCE_OF_ASSIGNMENT_EXPR = precedence({ type: "AssignmentExpression" }); const PRECEDENCE_OF_UPDATE_EXPR = precedence({ type: "UpdateExpression" }); /** * Determines if this rule should be enforced for a node given the current configuration. * @param {ASTNode} node - The node to be checked. * @returns {boolean} True if the rule should be enforced for this node. * @private */ function ruleApplies(node) { if (node.type === "JSXElement" || node.type === "JSXFragment") { const isSingleLine = node.loc.start.line === node.loc.end.line; switch (IGNORE_JSX) { // Exclude this JSX element from linting case "all": return false; // Exclude this JSX element if it is multi-line element case "multi-line": return isSingleLine; // Exclude this JSX element if it is single-line element case "single-line": return !isSingleLine; // Nothing special to be done for JSX elements case "none": break; // no default } } return ALL_NODES || node.type === "FunctionExpression" || node.type === "ArrowFunctionExpression"; } /** * Determines if a node is surrounded by parentheses twice. * @param {ASTNode} node - The node to be checked. * @returns {boolean} True if the node is doubly parenthesised. * @private */ function isParenthesisedTwice(node) { const previousToken = sourceCode.getTokenBefore(node, 1), nextToken = sourceCode.getTokenAfter(node, 1); return isParenthesised(node) && previousToken && nextToken && astUtils.isOpeningParenToken(previousToken) && previousToken.range[1] <= node.range[0] && astUtils.isClosingParenToken(nextToken) && nextToken.range[0] >= node.range[1]; } /** * Determines if a node is surrounded by (potentially) invalid parentheses. * @param {ASTNode} node - The node to be checked. * @returns {boolean} True if the node is incorrectly parenthesised. * @private */ function hasExcessParens(node) { return ruleApplies(node) && isParenthesised(node); } /** * Determines if a node that is expected to be parenthesised is surrounded by * (potentially) invalid extra parentheses. * @param {ASTNode} node - The node to be checked. * @returns {boolean} True if the node is has an unexpected extra pair of parentheses. * @private */ function hasDoubleExcessParens(node) { return ruleApplies(node) && isParenthesisedTwice(node); } /** * Determines if a node test expression is allowed to have a parenthesised assignment * @param {ASTNode} node - The node to be checked. * @returns {boolean} True if the assignment can be parenthesised. * @private */ function isCondAssignException(node) { return EXCEPT_COND_ASSIGN && node.test.type === "AssignmentExpression"; } /** * Determines if a node is in a return statement * @param {ASTNode} node - The node to be checked. * @returns {boolean} True if the node is in a return statement. * @private */ function isInReturnStatement(node) { for (let currentNode = node; currentNode; currentNode = currentNode.parent) { if ( currentNode.type === "ReturnStatement" || (currentNode.type === "ArrowFunctionExpression" && currentNode.body.type !== "BlockStatement") ) { return true; } } return false; } /** * Determines if a constructor function is newed-up with parens * @param {ASTNode} newExpression - The NewExpression node to be checked. * @returns {boolean} True if the constructor is called with parens. * @private */ function isNewExpressionWithParens(newExpression) { const lastToken = sourceCode.getLastToken(newExpression); const penultimateToken = sourceCode.getTokenBefore(lastToken); return newExpression.arguments.length > 0 || astUtils.isOpeningParenToken(penultimateToken) && astUtils.isClosingParenToken(lastToken); } /** * Determines if a node is or contains an assignment expression * @param {ASTNode} node - The node to be checked. * @returns {boolean} True if the node is or contains an assignment expression. * @private */ function containsAssignment(node) { if (node.type === "AssignmentExpression") { return true; } if (node.type === "ConditionalExpression" && (node.consequent.type === "AssignmentExpression" || node.alternate.type === "AssignmentExpression")) { return true; } if ((node.left && node.left.type === "AssignmentExpression") || (node.right && node.right.type === "AssignmentExpression")) { return true; } return false; } /** * Determines if a node is contained by or is itself a return statement and is allowed to have a parenthesised assignment * @param {ASTNode} node - The node to be checked. * @returns {boolean} True if the assignment can be parenthesised. * @private */ function isReturnAssignException(node) { if (!EXCEPT_RETURN_ASSIGN || !isInReturnStatement(node)) { return false; } if (node.type === "ReturnStatement") { return node.argument && containsAssignment(node.argument); } if (node.type === "ArrowFunctionExpression" && node.body.type !== "BlockStatement") { return containsAssignment(node.body); } return containsAssignment(node); } /** * Determines if a node following a [no LineTerminator here] restriction is * surrounded by (potentially) invalid extra parentheses. * @param {Token} token - The token preceding the [no LineTerminator here] restriction. * @param {ASTNode} node - The node to be checked. * @returns {boolean} True if the node is incorrectly parenthesised. * @private */ function hasExcessParensNoLineTerminator(token, node) { if (token.loc.end.line === node.loc.start.line) { return hasExcessParens(node); } return hasDoubleExcessParens(node); } /** * Determines whether a node should be preceded by an additional space when removing parens * @param {ASTNode} node node to evaluate; must be surrounded by parentheses * @returns {boolean} `true` if a space should be inserted before the node * @private */ function requiresLeadingSpace(node) { const leftParenToken = sourceCode.getTokenBefore(node); const tokenBeforeLeftParen = sourceCode.getTokenBefore(node, 1); const firstToken = sourceCode.getFirstToken(node); return tokenBeforeLeftParen && tokenBeforeLeftParen.range[1] === leftParenToken.range[0] && leftParenToken.range[1] === firstToken.range[0] && !astUtils.canTokensBeAdjacent(tokenBeforeLeftParen, firstToken); } /** * Determines whether a node should be followed by an additional space when removing parens * @param {ASTNode} node node to evaluate; must be surrounded by parentheses * @returns {boolean} `true` if a space should be inserted after the node * @private */ function requiresTrailingSpace(node) { const nextTwoTokens = sourceCode.getTokensAfter(node, { count: 2 }); const rightParenToken = nextTwoTokens[0]; const tokenAfterRightParen = nextTwoTokens[1]; const tokenBeforeRightParen = sourceCode.getLastToken(node); return rightParenToken && tokenAfterRightParen && !sourceCode.isSpaceBetweenTokens(rightParenToken, tokenAfterRightParen) && !astUtils.canTokensBeAdjacent(tokenBeforeRightParen, tokenAfterRightParen); } /** * Determines if a given expression node is an IIFE * @param {ASTNode} node The node to check * @returns {boolean} `true` if the given node is an IIFE */ function isIIFE(node) { return node.type === "CallExpression" && node.callee.type === "FunctionExpression"; } /** * Report the node * @param {ASTNode} node node to evaluate * @returns {void} * @private */ function report(node) { const leftParenToken = sourceCode.getTokenBefore(node); const rightParenToken = sourceCode.getTokenAfter(node); if (!isParenthesisedTwice(node)) { if (tokensToIgnore.has(sourceCode.getFirstToken(node))) { return; } if (isIIFE(node) && !isParenthesised(node.callee)) { return; } } context.report({ node, loc: leftParenToken.loc.start, messageId: "unexpected", fix(fixer) { const parenthesizedSource = sourceCode.text.slice(leftParenToken.range[1], rightParenToken.range[0]); return fixer.replaceTextRange([ leftParenToken.range[0], rightParenToken.range[1] ], (requiresLeadingSpace(node) ? " " : "") + parenthesizedSource + (requiresTrailingSpace(node) ? " " : "")); } }); } /** * Evaluate Unary update * @param {ASTNode} node node to evaluate * @returns {void} * @private */ function checkUnaryUpdate(node) { if (node.type === "UnaryExpression" && node.argument.type === "BinaryExpression" && node.argument.operator === "**") { return; } if (hasExcessParens(node.argument) && precedence(node.argument) >= precedence(node)) { report(node.argument); } } /** * Check if a member expression contains a call expression * @param {ASTNode} node MemberExpression node to evaluate * @returns {boolean} true if found, false if not */ function doesMemberExpressionContainCallExpression(node) { let currentNode = node.object; let currentNodeType = node.object.type; while (currentNodeType === "MemberExpression") { currentNode = currentNode.object; currentNodeType = currentNode.type; } return currentNodeType === "CallExpression"; } /** * Evaluate a new call * @param {ASTNode} node node to evaluate * @returns {void} * @private */ function checkCallNew(node) { const callee = node.callee; if (hasExcessParens(callee) && precedence(callee) >= precedence(node)) { const hasNewParensException = callee.type === "NewExpression" && !isNewExpressionWithParens(callee); if ( hasDoubleExcessParens(callee) || !isIIFE(node) && !hasNewParensException && !( /* * Allow extra parens around a new expression if * there are intervening parentheses. */ (callee.type === "MemberExpression" && doesMemberExpressionContainCallExpression(callee)) ) ) { report(node.callee); } } if (node.arguments.length === 1) { if (hasDoubleExcessParens(node.arguments[0]) && precedence(node.arguments[0]) >= PRECEDENCE_OF_ASSIGNMENT_EXPR) { report(node.arguments[0]); } } else { node.arguments .filter(arg => hasExcessParens(arg) && precedence(arg) >= PRECEDENCE_OF_ASSIGNMENT_EXPR) .forEach(report); } } /** * Evaluate binary logicals * @param {ASTNode} node node to evaluate * @returns {void} * @private */ function checkBinaryLogical(node) { const prec = precedence(node); const leftPrecedence = precedence(node.left); const rightPrecedence = precedence(node.right); const isExponentiation = node.operator === "**"; const shouldSkipLeft = (NESTED_BINARY && (node.left.type === "BinaryExpression" || node.left.type === "LogicalExpression")) || node.left.type === "UnaryExpression" && isExponentiation; const shouldSkipRight = NESTED_BINARY && (node.right.type === "BinaryExpression" || node.right.type === "LogicalExpression"); if (!shouldSkipLeft && hasExcessParens(node.left) && (leftPrecedence > prec || (leftPrecedence === prec && !isExponentiation))) { report(node.left); } if (!shouldSkipRight && hasExcessParens(node.right) && (rightPrecedence > prec || (rightPrecedence === prec && isExponentiation))) { report(node.right); } } /** * Check the parentheses around the super class of the given class definition. * @param {ASTNode} node The node of class declarations to check. * @returns {void} */ function checkClass(node) { if (!node.superClass) { return; } /* * If `node.superClass` is a LeftHandSideExpression, parentheses are extra. * Otherwise, parentheses are needed. */ const hasExtraParens = precedence(node.superClass) > PRECEDENCE_OF_UPDATE_EXPR ? hasExcessParens(node.superClass) : hasDoubleExcessParens(node.superClass); if (hasExtraParens) { report(node.superClass); } } /** * Check the parentheses around the argument of the given spread operator. * @param {ASTNode} node The node of spread elements/properties to check. * @returns {void} */ function checkSpreadOperator(node) { const hasExtraParens = precedence(node.argument) >= PRECEDENCE_OF_ASSIGNMENT_EXPR ? hasExcessParens(node.argument) : hasDoubleExcessParens(node.argument); if (hasExtraParens) { report(node.argument); } } /** * Checks the parentheses for an ExpressionStatement or ExportDefaultDeclaration * @param {ASTNode} node The ExpressionStatement.expression or ExportDefaultDeclaration.declaration node * @returns {void} */ function checkExpressionOrExportStatement(node) { const firstToken = isParenthesised(node) ? sourceCode.getTokenBefore(node) : sourceCode.getFirstToken(node); const secondToken = sourceCode.getTokenAfter(firstToken, astUtils.isNotOpeningParenToken); const thirdToken = secondToken ? sourceCode.getTokenAfter(secondToken) : null; const tokenAfterClosingParens = secondToken ? sourceCode.getTokenAfter(secondToken, astUtils.isNotClosingParenToken) : null; if ( astUtils.isOpeningParenToken(firstToken) && ( astUtils.isOpeningBraceToken(secondToken) || secondToken.type === "Keyword" && ( secondToken.value === "function" || secondToken.value === "class" || secondToken.value === "let" && tokenAfterClosingParens && ( astUtils.isOpeningBracketToken(tokenAfterClosingParens) || tokenAfterClosingParens.type === "Identifier" ) ) || secondToken && secondToken.type === "Identifier" && secondToken.value === "async" && thirdToken && thirdToken.type === "Keyword" && thirdToken.value === "function" ) ) { tokensToIgnore.add(secondToken); } if (hasExcessParens(node)) { report(node); } } return { ArrayExpression(node) { node.elements .filter(e => e && hasExcessParens(e) && precedence(e) >= PRECEDENCE_OF_ASSIGNMENT_EXPR) .forEach(report); }, ArrowFunctionExpression(node) { if (isReturnAssignException(node)) { return; } if (node.body.type === "ConditionalExpression" && IGNORE_ARROW_CONDITIONALS && !isParenthesisedTwice(node.body) ) { return; } if (node.body.type !== "BlockStatement") { const firstBodyToken = sourceCode.getFirstToken(node.body, astUtils.isNotOpeningParenToken); const tokenBeforeFirst = sourceCode.getTokenBefore(firstBodyToken); if (astUtils.isOpeningParenToken(tokenBeforeFirst) && astUtils.isOpeningBraceToken(firstBodyToken)) { tokensToIgnore.add(firstBodyToken); } if (hasExcessParens(node.body) && precedence(node.body) >= PRECEDENCE_OF_ASSIGNMENT_EXPR) { report(node.body); } } }, AssignmentExpression(node) { if (isReturnAssignException(node)) { return; } if (hasExcessParens(node.right) && precedence(node.right) >= precedence(node)) { report(node.right); } }, BinaryExpression: checkBinaryLogical, CallExpression: checkCallNew, ConditionalExpression(node) { if (isReturnAssignException(node)) { return; } if (hasExcessParens(node.test) && precedence(node.test) >= precedence({ type: "LogicalExpression", operator: "||" })) { report(node.test); } if (hasExcessParens(node.consequent) && precedence(node.consequent) >= PRECEDENCE_OF_ASSIGNMENT_EXPR) { report(node.consequent); } if (hasExcessParens(node.alternate) && precedence(node.alternate) >= PRECEDENCE_OF_ASSIGNMENT_EXPR) { report(node.alternate); } }, DoWhileStatement(node) { if (hasDoubleExcessParens(node.test) && !isCondAssignException(node)) { report(node.test); } }, ExportDefaultDeclaration: node => checkExpressionOrExportStatement(node.declaration), ExpressionStatement: node => checkExpressionOrExportStatement(node.expression), "ForInStatement, ForOfStatement"(node) { if (node.left.type !== "VariableDeclarator") { const firstLeftToken = sourceCode.getFirstToken(node.left, astUtils.isNotOpeningParenToken); if ( firstLeftToken.value === "let" && ( /* * If `let` is the only thing on the left side of the loop, it's the loop variable: `for ((let) of foo);` * Removing it will cause a syntax error, because it will be parsed as the start of a VariableDeclarator. */ (firstLeftToken.range[1] === node.left.range[1] || /* * If `let` is followed by a `[` token, it's a property access on the `let` value: `for ((let[foo]) of bar);` * Removing it will cause the property access to be parsed as a destructuring declaration of `foo` instead. */ astUtils.isOpeningBracketToken( sourceCode.getTokenAfter(firstLeftToken, astUtils.isNotClosingParenToken) )) ) ) { tokensToIgnore.add(firstLeftToken); } } if (!(node.type === "ForOfStatement" && node.right.type === "SequenceExpression") && hasExcessParens(node.right)) { report(node.right); } if (hasExcessParens(node.left)) { report(node.left); } }, ForStatement(node) { if (node.init && hasExcessParens(node.init)) { report(node.init); } if (node.test && hasExcessParens(node.test) && !isCondAssignException(node)) { report(node.test); } if (node.update && hasExcessParens(node.update)) { report(node.update); } }, IfStatement(node) { if (hasDoubleExcessParens(node.test) && !isCondAssignException(node)) { report(node.test); } }, LogicalExpression: checkBinaryLogical, MemberExpression(node) { const nodeObjHasExcessParens = hasExcessParens(node.object); if ( nodeObjHasExcessParens && precedence(node.object) >= precedence(node) && ( node.computed || !( astUtils.isDecimalInteger(node.object) || // RegExp literal is allowed to have parens (#1589) (node.object.type === "Literal" && node.object.regex) ) ) ) { report(node.object); } if (nodeObjHasExcessParens && node.object.type === "CallExpression" && node.parent.type !== "NewExpression") { report(node.object); } if (node.computed && hasExcessParens(node.property)) { report(node.property); } }, NewExpression: checkCallNew, ObjectExpression(node) { node.properties .filter(property => { const value = property.value; return value && hasExcessParens(value) && precedence(value) >= PRECEDENCE_OF_ASSIGNMENT_EXPR; }).forEach(property => report(property.value)); }, ReturnStatement(node) { const returnToken = sourceCode.getFirstToken(node); if (isReturnAssignException(node)) { return; } if (node.argument && hasExcessParensNoLineTerminator(returnToken, node.argument) && // RegExp literal is allowed to have parens (#1589) !(node.argument.type === "Literal" && node.argument.regex)) { report(node.argument); } }, SequenceExpression(node) { node.expressions .filter(e => hasExcessParens(e) && precedence(e) >= precedence(node)) .forEach(report); }, SwitchCase(node) { if (node.test && hasExcessParens(node.test)) { report(node.test); } }, SwitchStatement(node) { if (hasDoubleExcessParens(node.discriminant)) { report(node.discriminant); } }, ThrowStatement(node) { const throwToken = sourceCode.getFirstToken(node); if (hasExcessParensNoLineTerminator(throwToken, node.argument)) { report(node.argument); } }, UnaryExpression: checkUnaryUpdate, UpdateExpression: checkUnaryUpdate, AwaitExpression: checkUnaryUpdate, VariableDeclarator(node) { if (node.init && hasExcessParens(node.init) && precedence(node.init) >= PRECEDENCE_OF_ASSIGNMENT_EXPR && // RegExp literal is allowed to have parens (#1589) !(node.init.type === "Literal" && node.init.regex)) { report(node.init); } }, WhileStatement(node) { if (hasDoubleExcessParens(node.test) && !isCondAssignException(node)) { report(node.test); } }, WithStatement(node) { if (hasDoubleExcessParens(node.object)) { report(node.object); } }, YieldExpression(node) { if (node.argument) { const yieldToken = sourceCode.getFirstToken(node); if ((precedence(node.argument) >= precedence(node) && hasExcessParensNoLineTerminator(yieldToken, node.argument)) || hasDoubleExcessParens(node.argument)) { report(node.argument); } } }, ClassDeclaration: checkClass, ClassExpression: checkClass, SpreadElement: checkSpreadOperator, SpreadProperty: checkSpreadOperator, ExperimentalSpreadProperty: checkSpreadOperator }; } };