.config/coc/extensions/node_modules/coc-prettier/node_modules/eslint/lib/rules/no-unused-expressions.js

   1 /**
   2  * @fileoverview Flag expressions in statement position that do not side effect
   3  * @author Michael Ficarra
   4  */
   5 "use strict";
   6
   7 //------------------------------------------------------------------------------
   8 // Rule Definition
   9 //------------------------------------------------------------------------------
  10
  11 module.exports = {
  12     meta: {
  13         type: "suggestion",
  14
  15         docs: {
  16             description: "disallow unused expressions",
  17             category: "Best Practices",
  18             recommended: false,
  19             url: "https://eslint.org/docs/rules/no-unused-expressions"
  20         },
  21
  22         schema: [
  23             {
  24                 type: "object",
  25                 properties: {
  26                     allowShortCircuit: {
  27                         type: "boolean",
  28                         default: false
  29                     },
  30                     allowTernary: {
  31                         type: "boolean",
  32                         default: false
  33                     },
  34                     allowTaggedTemplates: {
  35                         type: "boolean",
  36                         default: false
  37                     }
  38                 },
  39                 additionalProperties: false
  40             }
  41         ]
  42     },
  43
  44     create(context) {
  45         const config = context.options[0] || {},
  46             allowShortCircuit = config.allowShortCircuit || false,
  47             allowTernary = config.allowTernary || false,
  48             allowTaggedTemplates = config.allowTaggedTemplates || false;
  49
  50         // eslint-disable-next-line jsdoc/require-description
  51         /**
  52          * @param {ASTNode} node any node
  53          * @returns {boolean} whether the given node structurally represents a directive
  54          */
  55         function looksLikeDirective(node) {
  56             return node.type === "ExpressionStatement" &&
  57                 node.expression.type === "Literal" && typeof node.expression.value === "string";
  58         }
  59
  60         // eslint-disable-next-line jsdoc/require-description
  61         /**
  62          * @param {Function} predicate ([a] -> Boolean) the function used to make the determination
  63          * @param {a[]} list the input list
  64          * @returns {a[]} the leading sequence of members in the given list that pass the given predicate
  65          */
  66         function takeWhile(predicate, list) {
  67             for (let i = 0; i < list.length; ++i) {
  68                 if (!predicate(list[i])) {
  69                     return list.slice(0, i);
  70                 }
  71             }
  72             return list.slice();
  73         }
  74
  75         // eslint-disable-next-line jsdoc/require-description
  76         /**
  77          * @param {ASTNode} node a Program or BlockStatement node
  78          * @returns {ASTNode[]} the leading sequence of directive nodes in the given node's body
  79          */
  80         function directives(node) {
  81             return takeWhile(looksLikeDirective, node.body);
  82         }
  83
  84         // eslint-disable-next-line jsdoc/require-description
  85         /**
  86          * @param {ASTNode} node any node
  87          * @param {ASTNode[]} ancestors the given node's ancestors
  88          * @returns {boolean} whether the given node is considered a directive in its current position
  89          */
  90         function isDirective(node, ancestors) {
  91             const parent = ancestors[ancestors.length - 1],
  92                 grandparent = ancestors[ancestors.length - 2];
  93
  94             return (parent.type === "Program" || parent.type === "BlockStatement" &&
  95                     (/Function/u.test(grandparent.type))) &&
  96                     directives(parent).indexOf(node) >= 0;
  97         }
  98
  99         /**
 100          * Determines whether or not a given node is a valid expression. Recurses on short circuit eval and ternary nodes if enabled by flags.
 101          * @param {ASTNode} node any node
 102          * @returns {boolean} whether the given node is a valid expression
 103          */
 104         function isValidExpression(node) {
 105             if (allowTernary) {
 106
 107                 // Recursive check for ternary and logical expressions
 108                 if (node.type === "ConditionalExpression") {
 109                     return isValidExpression(node.consequent) && isValidExpression(node.alternate);
 110                 }
 111             }
 112
 113             if (allowShortCircuit) {
 114                 if (node.type === "LogicalExpression") {
 115                     return isValidExpression(node.right);
 116                 }
 117             }
 118
 119             if (allowTaggedTemplates && node.type === "TaggedTemplateExpression") {
 120                 return true;
 121             }
 122
 123             return /^(?:Assignment|Call|New|Update|Yield|Await)Expression$/u.test(node.type) ||
 124                 (node.type === "UnaryExpression" && ["delete", "void"].indexOf(node.operator) >= 0);
 125         }
 126
 127         return {
 128             ExpressionStatement(node) {
 129                 if (!isValidExpression(node.expression) && !isDirective(node, context.getAncestors())) {
 130                     context.report({ node, message: "Expected an assignment or function call and instead saw an expression." });
 131                 }
 132             }
 133         };
 134
 135     }
 136 };