137 lines
4.9 KiB
JavaScript
137 lines
4.9 KiB
JavaScript
/**
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* @fileoverview Flag expressions in statement position that do not side effect
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* @author Michael Ficarra
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*/
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"use strict";
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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: "disallow unused expressions",
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category: "Best Practices",
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recommended: false,
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url: "https://eslint.org/docs/rules/no-unused-expressions"
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},
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schema: [
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{
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type: "object",
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properties: {
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allowShortCircuit: {
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type: "boolean",
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default: false
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},
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allowTernary: {
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type: "boolean",
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default: false
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},
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allowTaggedTemplates: {
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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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},
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create(context) {
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const config = context.options[0] || {},
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allowShortCircuit = config.allowShortCircuit || false,
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allowTernary = config.allowTernary || false,
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allowTaggedTemplates = config.allowTaggedTemplates || false;
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// eslint-disable-next-line jsdoc/require-description
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/**
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* @param {ASTNode} node any node
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* @returns {boolean} whether the given node structurally represents a directive
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*/
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function looksLikeDirective(node) {
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return node.type === "ExpressionStatement" &&
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node.expression.type === "Literal" && typeof node.expression.value === "string";
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}
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// eslint-disable-next-line jsdoc/require-description
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/**
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* @param {Function} predicate ([a] -> Boolean) the function used to make the determination
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* @param {a[]} list the input list
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* @returns {a[]} the leading sequence of members in the given list that pass the given predicate
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*/
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function takeWhile(predicate, list) {
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for (let i = 0; i < list.length; ++i) {
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if (!predicate(list[i])) {
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return list.slice(0, i);
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}
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}
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return list.slice();
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}
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// eslint-disable-next-line jsdoc/require-description
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/**
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* @param {ASTNode} node a Program or BlockStatement node
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* @returns {ASTNode[]} the leading sequence of directive nodes in the given node's body
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*/
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function directives(node) {
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return takeWhile(looksLikeDirective, node.body);
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}
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// eslint-disable-next-line jsdoc/require-description
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/**
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* @param {ASTNode} node any node
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* @param {ASTNode[]} ancestors the given node's ancestors
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* @returns {boolean} whether the given node is considered a directive in its current position
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*/
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function isDirective(node, ancestors) {
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const parent = ancestors[ancestors.length - 1],
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grandparent = ancestors[ancestors.length - 2];
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return (parent.type === "Program" || parent.type === "BlockStatement" &&
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(/Function/u.test(grandparent.type))) &&
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directives(parent).indexOf(node) >= 0;
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}
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/**
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* Determines whether or not a given node is a valid expression. Recurses on short circuit eval and ternary nodes if enabled by flags.
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* @param {ASTNode} node any node
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* @returns {boolean} whether the given node is a valid expression
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*/
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function isValidExpression(node) {
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if (allowTernary) {
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// Recursive check for ternary and logical expressions
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if (node.type === "ConditionalExpression") {
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return isValidExpression(node.consequent) && isValidExpression(node.alternate);
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}
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}
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if (allowShortCircuit) {
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if (node.type === "LogicalExpression") {
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return isValidExpression(node.right);
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}
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}
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if (allowTaggedTemplates && node.type === "TaggedTemplateExpression") {
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return true;
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}
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return /^(?:Assignment|Call|New|Update|Yield|Await)Expression$/u.test(node.type) ||
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(node.type === "UnaryExpression" && ["delete", "void"].indexOf(node.operator) >= 0);
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}
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return {
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ExpressionStatement(node) {
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if (!isValidExpression(node.expression) && !isDirective(node, context.getAncestors())) {
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context.report({ node, message: "Expected an assignment or function call and instead saw an expression." });
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}
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}
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};
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}
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};
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