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September 14, 2020 10:42
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Ignoring revisions in .git-blame-ignore-revs.
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/**
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* @fileoverview Rule to replace assignment expressions with operator assignment
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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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//------------------------------------------------------------------------------
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// Helpers
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//------------------------------------------------------------------------------
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/**
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* Checks whether an operator is commutative and has an operator assignment
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* shorthand form.
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* @param {string} operator Operator to check.
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* @returns {boolean} True if the operator is commutative and has a
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* shorthand form.
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*/
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function isCommutativeOperatorWithShorthand(operator) {
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}
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/**
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* Checks whether an operator is not commutative and has an operator assignment
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* shorthand form.
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* @param {string} operator Operator to check.
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* @returns {boolean} True if the operator is not commutative and has
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* a shorthand form.
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*/
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function isNonCommutativeOperatorWithShorthand(operator) {
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}
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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/**
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* Determines if the left side of a node can be safely fixed (i.e. if it activates the same getters/setters and)
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* toString calls regardless of whether assignment shorthand is used)
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* @param {ASTNode} node The node on the left side of the expression
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* @returns {boolean} `true` if the node can be fixed
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*/
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function canBeFixed(node) {
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return (
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node.type === "Identifier" ||
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(
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node.type === "MemberExpression" &&
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(node.object.type === "Identifier" || node.object.type === "ThisExpression") &&
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(!node.computed || node.property.type === "Literal")
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)
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);
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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: "Require or disallow assignment operator shorthand where possible",
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recommended: false,
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},
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schema: [
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{
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enum: ["always", "never"]
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}
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],
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fixable: "code",
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messages: {
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replaced: "Assignment (=) can be replaced with operator assignment ({{operator}}).",
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unexpected: "Unexpected operator assignment ({{operator}}) shorthand."
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}
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},
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create(context) {
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/**
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* Returns the operator token of an AssignmentExpression or BinaryExpression
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* @param {ASTNode} node An AssignmentExpression or BinaryExpression node
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* @returns {Token} The operator token in the node
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*/
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function getOperatorToken(node) {
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return sourceCode.getFirstTokenBetween(node.left, node.right, token => token.value === node.operator);
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}
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/**
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* Ensures that an assignment uses the shorthand form where possible.
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* @returns {void}
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*/
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function verify(node) {
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if (node.operator !== "=" || node.right.type !== "BinaryExpression") {
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return;
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}
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const left = node.left;
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const expr = node.right;
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const operator = expr.operator;
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if (isCommutativeOperatorWithShorthand(operator) || isNonCommutativeOperatorWithShorthand(operator)) {
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if (astUtils.isSameReference(left, expr.left, true)) {
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context.report({
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node,
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messageId: "replaced",
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fix(fixer) {
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if (canBeFixed(left) && canBeFixed(expr.left)) {
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const equalsToken = getOperatorToken(node);
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const operatorToken = getOperatorToken(expr);
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const leftText = sourceCode.getText().slice(node.range[0], equalsToken.range[0]);
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const rightText = sourceCode.getText().slice(operatorToken.range[1], node.right.range[1]);
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// Check for comments that would be removed.
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if (sourceCode.commentsExistBetween(equalsToken, operatorToken)) {
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return null;
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}
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return fixer.replaceText(node, `${leftText}${replacementOperator}${rightText}`);
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}
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return null;
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}
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});
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} else if (astUtils.isSameReference(left, expr.right, true) && isCommutativeOperatorWithShorthand(operator)) {
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/*
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* This case can't be fixed safely.
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* If `a` and `b` both have custom valueOf() behavior, then fixing `a = b * a` to `a *= b` would
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* change the execution order of the valueOf() functions.
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*/
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context.report({
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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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* Warns if an assignment expression uses operator assignment shorthand.
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* @returns {void}
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*/
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function prohibit(node) {
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if (node.operator !== "=" && !astUtils.isLogicalAssignmentOperator(node.operator)) {
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context.report({
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node,
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messageId: "unexpected",
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fix(fixer) {
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if (canBeFixed(node.left)) {
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const firstToken = sourceCode.getFirstToken(node);
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const operatorToken = getOperatorToken(node);
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const leftText = sourceCode.getText().slice(node.range[0], operatorToken.range[0]);
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const newOperator = node.operator.slice(0, -1);
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let rightText;
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// Check for comments that would be duplicated.
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if (sourceCode.commentsExistBetween(firstToken, operatorToken)) {
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return null;
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}
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// If this change would modify precedence (e.g. `foo *= bar + 1` => `foo = foo * (bar + 1)`), parenthesize the right side.
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if (
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astUtils.getPrecedence(node.right) <= astUtils.getPrecedence({ type: "BinaryExpression", operator: newOperator }) &&
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!astUtils.isParenthesised(sourceCode, node.right)
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) {
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rightText = `${sourceCode.text.slice(operatorToken.range[1], node.right.range[0])}(${sourceCode.getText(node.right)})`;
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} else {
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const tokenAfterOperator = sourceCode.getTokenAfter(operatorToken, { includeComments: true });
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let rightTextPrefix = "";
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if (
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operatorToken.range[1] === tokenAfterOperator.range[0] &&
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!astUtils.canTokensBeAdjacent({ type: "Punctuator", value: newOperator }, tokenAfterOperator)
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) {
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rightTextPrefix = " "; // foo+=+bar -> foo= foo+ +bar
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}
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rightText = `${rightTextPrefix}${sourceCode.text.slice(operatorToken.range[1], node.range[1])}`;
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}
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return fixer.replaceText(node, `${leftText}= ${leftText}${newOperator}${rightText}`);
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}
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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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return {
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AssignmentExpression: context.options[0] !== "never" ? verify : prohibit
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};
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}
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};