328 lines
11 KiB
JavaScript
328 lines
11 KiB
JavaScript
/**
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* @fileoverview Rule to require or disallow yoda comparisons
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* @author Nicholas C. Zakas
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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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* Determines whether an operator is a comparison operator.
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* @param {string} operator The operator to check.
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* @returns {boolean} Whether or not it is a comparison operator.
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*/
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function isComparisonOperator(operator) {
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return (/^(==|===|!=|!==|<|>|<=|>=)$/u).test(operator);
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}
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/**
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* Determines whether an operator is an equality operator.
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* @param {string} operator The operator to check.
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* @returns {boolean} Whether or not it is an equality operator.
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*/
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function isEqualityOperator(operator) {
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return (/^(==|===)$/u).test(operator);
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}
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/**
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* Determines whether an operator is one used in a range test.
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* Allowed operators are `<` and `<=`.
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* @param {string} operator The operator to check.
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* @returns {boolean} Whether the operator is used in range tests.
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*/
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function isRangeTestOperator(operator) {
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return ["<", "<="].indexOf(operator) >= 0;
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}
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/**
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* Determines whether a non-Literal node is a negative number that should be
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* treated as if it were a single Literal node.
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* @param {ASTNode} node Node to test.
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* @returns {boolean} True if the node is a negative number that looks like a
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* real literal and should be treated as such.
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*/
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function looksLikeLiteral(node) {
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return (node.type === "UnaryExpression" &&
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node.operator === "-" &&
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node.prefix &&
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node.argument.type === "Literal" &&
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typeof node.argument.value === "number");
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}
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/**
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* Attempts to derive a Literal node from nodes that are treated like literals.
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* @param {ASTNode} node Node to normalize.
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* @param {number} [defaultValue] The default value to be returned if the node
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* is not a Literal.
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* @returns {ASTNode} One of the following options.
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* 1. The original node if the node is already a Literal
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* 2. A normalized Literal node with the negative number as the value if the
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* node represents a negative number literal.
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* 3. The Literal node which has the `defaultValue` argument if it exists.
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* 4. Otherwise `null`.
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*/
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function getNormalizedLiteral(node, defaultValue) {
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if (node.type === "Literal") {
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return node;
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}
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if (looksLikeLiteral(node)) {
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return {
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type: "Literal",
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value: -node.argument.value,
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raw: `-${node.argument.value}`
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};
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}
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if (defaultValue) {
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return {
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type: "Literal",
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value: defaultValue,
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raw: String(defaultValue)
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};
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}
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return null;
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}
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/**
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* Checks whether two expressions reference the same value. For example:
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* a = a
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* a.b = a.b
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* a[0] = a[0]
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* a['b'] = a['b']
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* @param {ASTNode} a Left side of the comparison.
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* @param {ASTNode} b Right side of the comparison.
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* @returns {boolean} True if both sides match and reference the same value.
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*/
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function same(a, b) {
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if (a.type !== b.type) {
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return false;
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}
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switch (a.type) {
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case "Identifier":
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return a.name === b.name;
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case "Literal":
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return a.value === b.value;
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case "MemberExpression": {
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const nameA = astUtils.getStaticPropertyName(a);
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// x.y = x["y"]
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if (nameA !== null) {
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return (
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same(a.object, b.object) &&
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nameA === astUtils.getStaticPropertyName(b)
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);
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}
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/*
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* x[0] = x[0]
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* x[y] = x[y]
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* x.y = x.y
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*/
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return (
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a.computed === b.computed &&
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same(a.object, b.object) &&
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same(a.property, b.property)
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);
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}
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case "ThisExpression":
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return true;
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default:
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return false;
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}
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}
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//------------------------------------------------------------------------------
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// Rule Definition
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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 \"Yoda\" conditions",
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category: "Best Practices",
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recommended: false,
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url: "https://eslint.org/docs/rules/yoda"
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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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type: "object",
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properties: {
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exceptRange: {
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type: "boolean",
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default: false
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},
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onlyEquality: {
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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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],
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fixable: "code",
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messages: {
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expected: "Expected literal to be on the {{expectedSide}} side of {{operator}}."
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}
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},
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create(context) {
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// Default to "never" (!always) if no option
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const always = (context.options[0] === "always");
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const exceptRange = (context.options[1] && context.options[1].exceptRange);
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const onlyEquality = (context.options[1] && context.options[1].onlyEquality);
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const sourceCode = context.getSourceCode();
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/**
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* Determines whether node represents a range test.
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* A range test is a "between" test like `(0 <= x && x < 1)` or an "outside"
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* test like `(x < 0 || 1 <= x)`. It must be wrapped in parentheses, and
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* both operators must be `<` or `<=`. Finally, the literal on the left side
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* must be less than or equal to the literal on the right side so that the
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* test makes any sense.
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* @param {ASTNode} node LogicalExpression node to test.
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* @returns {boolean} Whether node is a range test.
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*/
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function isRangeTest(node) {
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const left = node.left,
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right = node.right;
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/**
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* Determines whether node is of the form `0 <= x && x < 1`.
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* @returns {boolean} Whether node is a "between" range test.
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*/
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function isBetweenTest() {
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let leftLiteral, rightLiteral;
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return (node.operator === "&&" &&
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(leftLiteral = getNormalizedLiteral(left.left)) &&
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(rightLiteral = getNormalizedLiteral(right.right, Number.POSITIVE_INFINITY)) &&
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leftLiteral.value <= rightLiteral.value &&
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same(left.right, right.left));
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}
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/**
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* Determines whether node is of the form `x < 0 || 1 <= x`.
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* @returns {boolean} Whether node is an "outside" range test.
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*/
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function isOutsideTest() {
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let leftLiteral, rightLiteral;
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return (node.operator === "||" &&
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(leftLiteral = getNormalizedLiteral(left.right, Number.NEGATIVE_INFINITY)) &&
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(rightLiteral = getNormalizedLiteral(right.left)) &&
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leftLiteral.value <= rightLiteral.value &&
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same(left.left, right.right));
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}
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/**
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* Determines whether node is wrapped in parentheses.
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* @returns {boolean} Whether node is preceded immediately by an open
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* paren token and followed immediately by a close
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* paren token.
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*/
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function isParenWrapped() {
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return astUtils.isParenthesised(sourceCode, node);
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}
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return (node.type === "LogicalExpression" &&
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left.type === "BinaryExpression" &&
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right.type === "BinaryExpression" &&
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isRangeTestOperator(left.operator) &&
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isRangeTestOperator(right.operator) &&
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(isBetweenTest() || isOutsideTest()) &&
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isParenWrapped());
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}
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const OPERATOR_FLIP_MAP = {
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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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">=": "<="
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};
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/**
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* Returns a string representation of a BinaryExpression node with its sides/operator flipped around.
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* @param {ASTNode} node The BinaryExpression node
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* @returns {string} A string representation of the node with the sides and operator flipped
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*/
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function getFlippedString(node) {
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const tokenBefore = sourceCode.getTokenBefore(node);
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const operatorToken = sourceCode.getFirstTokenBetween(node.left, node.right, token => token.value === node.operator);
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const textBeforeOperator = sourceCode.getText().slice(sourceCode.getTokenBefore(operatorToken).range[1], operatorToken.range[0]);
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const textAfterOperator = sourceCode.getText().slice(operatorToken.range[1], sourceCode.getTokenAfter(operatorToken).range[0]);
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const leftText = sourceCode.getText().slice(node.range[0], sourceCode.getTokenBefore(operatorToken).range[1]);
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const firstRightToken = sourceCode.getTokenAfter(operatorToken);
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const rightText = sourceCode.getText().slice(firstRightToken.range[0], node.range[1]);
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let prefix = "";
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if (tokenBefore && tokenBefore.range[1] === node.range[0] &&
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!astUtils.canTokensBeAdjacent(tokenBefore, firstRightToken)) {
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prefix = " ";
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}
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return prefix + rightText + textBeforeOperator + OPERATOR_FLIP_MAP[operatorToken.value] + textAfterOperator + leftText;
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}
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//--------------------------------------------------------------------------
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// Public
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//--------------------------------------------------------------------------
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return {
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BinaryExpression(node) {
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const expectedLiteral = always ? node.left : node.right;
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const expectedNonLiteral = always ? node.right : node.left;
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// If `expectedLiteral` is not a literal, and `expectedNonLiteral` is a literal, raise an error.
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if (
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(expectedNonLiteral.type === "Literal" || looksLikeLiteral(expectedNonLiteral)) &&
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!(expectedLiteral.type === "Literal" || looksLikeLiteral(expectedLiteral)) &&
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!(!isEqualityOperator(node.operator) && onlyEquality) &&
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isComparisonOperator(node.operator) &&
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!(exceptRange && isRangeTest(context.getAncestors().pop()))
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) {
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context.report({
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node,
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messageId: "expected",
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data: {
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operator: node.operator,
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expectedSide: always ? "left" : "right"
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},
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fix: fixer => fixer.replaceText(node, getFlippedString(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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};
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