1 | /**
|
2 | * @fileoverview Rule to replace assignment expressions with operator assignment
|
3 | * @author Brandon Mills
|
4 | */
|
5 | ;
|
6 |
|
7 | //------------------------------------------------------------------------------
|
8 | // Requirements
|
9 | //------------------------------------------------------------------------------
|
10 |
|
11 | const astUtils = require("./utils/ast-utils");
|
12 |
|
13 | //------------------------------------------------------------------------------
|
14 | // Helpers
|
15 | //------------------------------------------------------------------------------
|
16 |
|
17 | /**
|
18 | * Checks whether an operator is commutative and has an operator assignment
|
19 | * shorthand form.
|
20 | * @param {string} operator Operator to check.
|
21 | * @returns {boolean} True if the operator is commutative and has a
|
22 | * shorthand form.
|
23 | */
|
24 | function isCommutativeOperatorWithShorthand(operator) {
|
25 | return ["*", "&", "^", "|"].indexOf(operator) >= 0;
|
26 | }
|
27 |
|
28 | /**
|
29 | * Checks whether an operator is not commutative and has an operator assignment
|
30 | * shorthand form.
|
31 | * @param {string} operator Operator to check.
|
32 | * @returns {boolean} True if the operator is not commutative and has
|
33 | * a shorthand form.
|
34 | */
|
35 | function isNonCommutativeOperatorWithShorthand(operator) {
|
36 | return ["+", "-", "/", "%", "<<", ">>", ">>>", "**"].indexOf(operator) >= 0;
|
37 | }
|
38 |
|
39 | //------------------------------------------------------------------------------
|
40 | // Rule Definition
|
41 | //------------------------------------------------------------------------------
|
42 |
|
43 | /**
|
44 | * Determines if the left side of a node can be safely fixed (i.e. if it activates the same getters/setters and)
|
45 | * toString calls regardless of whether assignment shorthand is used)
|
46 | * @param {ASTNode} node The node on the left side of the expression
|
47 | * @returns {boolean} `true` if the node can be fixed
|
48 | */
|
49 | function canBeFixed(node) {
|
50 | return (
|
51 | node.type === "Identifier" ||
|
52 | (
|
53 | node.type === "MemberExpression" &&
|
54 | (node.object.type === "Identifier" || node.object.type === "ThisExpression") &&
|
55 | (!node.computed || node.property.type === "Literal")
|
56 | )
|
57 | );
|
58 | }
|
59 |
|
60 | module.exports = {
|
61 | meta: {
|
62 | type: "suggestion",
|
63 |
|
64 | docs: {
|
65 | description: "require or disallow assignment operator shorthand where possible",
|
66 | category: "Stylistic Issues",
|
67 | recommended: false,
|
68 | url: "https://eslint.org/docs/rules/operator-assignment"
|
69 | },
|
70 |
|
71 | schema: [
|
72 | {
|
73 | enum: ["always", "never"]
|
74 | }
|
75 | ],
|
76 |
|
77 | fixable: "code",
|
78 | messages: {
|
79 | replaced: "Assignment can be replaced with operator assignment.",
|
80 | unexpected: "Unexpected operator assignment shorthand."
|
81 | }
|
82 | },
|
83 |
|
84 | create(context) {
|
85 |
|
86 | const sourceCode = context.getSourceCode();
|
87 |
|
88 | /**
|
89 | * Returns the operator token of an AssignmentExpression or BinaryExpression
|
90 | * @param {ASTNode} node An AssignmentExpression or BinaryExpression node
|
91 | * @returns {Token} The operator token in the node
|
92 | */
|
93 | function getOperatorToken(node) {
|
94 | return sourceCode.getFirstTokenBetween(node.left, node.right, token => token.value === node.operator);
|
95 | }
|
96 |
|
97 | /**
|
98 | * Ensures that an assignment uses the shorthand form where possible.
|
99 | * @param {ASTNode} node An AssignmentExpression node.
|
100 | * @returns {void}
|
101 | */
|
102 | function verify(node) {
|
103 | if (node.operator !== "=" || node.right.type !== "BinaryExpression") {
|
104 | return;
|
105 | }
|
106 |
|
107 | const left = node.left;
|
108 | const expr = node.right;
|
109 | const operator = expr.operator;
|
110 |
|
111 | if (isCommutativeOperatorWithShorthand(operator) || isNonCommutativeOperatorWithShorthand(operator)) {
|
112 | if (astUtils.isSameReference(left, expr.left, true)) {
|
113 | context.report({
|
114 | node,
|
115 | messageId: "replaced",
|
116 | fix(fixer) {
|
117 | if (canBeFixed(left) && canBeFixed(expr.left)) {
|
118 | const equalsToken = getOperatorToken(node);
|
119 | const operatorToken = getOperatorToken(expr);
|
120 | const leftText = sourceCode.getText().slice(node.range[0], equalsToken.range[0]);
|
121 | const rightText = sourceCode.getText().slice(operatorToken.range[1], node.right.range[1]);
|
122 |
|
123 | // Check for comments that would be removed.
|
124 | if (sourceCode.commentsExistBetween(equalsToken, operatorToken)) {
|
125 | return null;
|
126 | }
|
127 |
|
128 | return fixer.replaceText(node, `${leftText}${expr.operator}=${rightText}`);
|
129 | }
|
130 | return null;
|
131 | }
|
132 | });
|
133 | } else if (astUtils.isSameReference(left, expr.right, true) && isCommutativeOperatorWithShorthand(operator)) {
|
134 |
|
135 | /*
|
136 | * This case can't be fixed safely.
|
137 | * If `a` and `b` both have custom valueOf() behavior, then fixing `a = b * a` to `a *= b` would
|
138 | * change the execution order of the valueOf() functions.
|
139 | */
|
140 | context.report({
|
141 | node,
|
142 | messageId: "replaced"
|
143 | });
|
144 | }
|
145 | }
|
146 | }
|
147 |
|
148 | /**
|
149 | * Warns if an assignment expression uses operator assignment shorthand.
|
150 | * @param {ASTNode} node An AssignmentExpression node.
|
151 | * @returns {void}
|
152 | */
|
153 | function prohibit(node) {
|
154 | if (node.operator !== "=" && !astUtils.isLogicalAssignmentOperator(node.operator)) {
|
155 | context.report({
|
156 | node,
|
157 | messageId: "unexpected",
|
158 | fix(fixer) {
|
159 | if (canBeFixed(node.left)) {
|
160 | const firstToken = sourceCode.getFirstToken(node);
|
161 | const operatorToken = getOperatorToken(node);
|
162 | const leftText = sourceCode.getText().slice(node.range[0], operatorToken.range[0]);
|
163 | const newOperator = node.operator.slice(0, -1);
|
164 | let rightText;
|
165 |
|
166 | // Check for comments that would be duplicated.
|
167 | if (sourceCode.commentsExistBetween(firstToken, operatorToken)) {
|
168 | return null;
|
169 | }
|
170 |
|
171 | // If this change would modify precedence (e.g. `foo *= bar + 1` => `foo = foo * (bar + 1)`), parenthesize the right side.
|
172 | if (
|
173 | astUtils.getPrecedence(node.right) <= astUtils.getPrecedence({ type: "BinaryExpression", operator: newOperator }) &&
|
174 | !astUtils.isParenthesised(sourceCode, node.right)
|
175 | ) {
|
176 | rightText = `${sourceCode.text.slice(operatorToken.range[1], node.right.range[0])}(${sourceCode.getText(node.right)})`;
|
177 | } else {
|
178 | const tokenAfterOperator = sourceCode.getTokenAfter(operatorToken, { includeComments: true });
|
179 | let rightTextPrefix = "";
|
180 |
|
181 | if (
|
182 | operatorToken.range[1] === tokenAfterOperator.range[0] &&
|
183 | !astUtils.canTokensBeAdjacent({ type: "Punctuator", value: newOperator }, tokenAfterOperator)
|
184 | ) {
|
185 | rightTextPrefix = " "; // foo+=+bar -> foo= foo+ +bar
|
186 | }
|
187 |
|
188 | rightText = `${rightTextPrefix}${sourceCode.text.slice(operatorToken.range[1], node.range[1])}`;
|
189 | }
|
190 |
|
191 | return fixer.replaceText(node, `${leftText}= ${leftText}${newOperator}${rightText}`);
|
192 | }
|
193 | return null;
|
194 | }
|
195 | });
|
196 | }
|
197 | }
|
198 |
|
199 | return {
|
200 | AssignmentExpression: context.options[0] !== "never" ? verify : prohibit
|
201 | };
|
202 |
|
203 | }
|
204 | };
|