.config/coc/extensions/node_modules/coc-prettier/node_modules/eslint/lib/rules/no-unneeded-ternary.js

   1 /**
   2  * @fileoverview Rule to flag no-unneeded-ternary
   3  * @author Gyandeep Singh
   4  */
   5
   6 "use strict";
   7
   8 const astUtils = require("./utils/ast-utils");
   9
  10 // Operators that always result in a boolean value
  11 const BOOLEAN_OPERATORS = new Set(["==", "===", "!=", "!==", ">", ">=", "<", "<=", "in", "instanceof"]);
  12 const OPERATOR_INVERSES = {
  13     "==": "!=",
  14     "!=": "==",
  15     "===": "!==",
  16     "!==": "==="
  17
  18     // Operators like < and >= are not true inverses, since both will return false with NaN.
  19 };
  20 const OR_PRECEDENCE = astUtils.getPrecedence({ type: "LogicalExpression", operator: "||" });
  21
  22 //------------------------------------------------------------------------------
  23 // Rule Definition
  24 //------------------------------------------------------------------------------
  25
  26 module.exports = {
  27     meta: {
  28         type: "suggestion",
  29
  30         docs: {
  31             description: "disallow ternary operators when simpler alternatives exist",
  32             category: "Stylistic Issues",
  33             recommended: false,
  34             url: "https://eslint.org/docs/rules/no-unneeded-ternary"
  35         },
  36
  37         schema: [
  38             {
  39                 type: "object",
  40                 properties: {
  41                     defaultAssignment: {
  42                         type: "boolean",
  43                         default: true
  44                     }
  45                 },
  46                 additionalProperties: false
  47             }
  48         ],
  49
  50         fixable: "code"
  51     },
  52
  53     create(context) {
  54         const options = context.options[0] || {};
  55         const defaultAssignment = options.defaultAssignment !== false;
  56         const sourceCode = context.getSourceCode();
  57
  58         /**
  59          * Test if the node is a boolean literal
  60          * @param {ASTNode} node The node to report.
  61          * @returns {boolean} True if the its a boolean literal
  62          * @private
  63          */
  64         function isBooleanLiteral(node) {
  65             return node.type === "Literal" && typeof node.value === "boolean";
  66         }
  67
  68         /**
  69          * Creates an expression that represents the boolean inverse of the expression represented by the original node
  70          * @param {ASTNode} node A node representing an expression
  71          * @returns {string} A string representing an inverted expression
  72          */
  73         function invertExpression(node) {
  74             if (node.type === "BinaryExpression" && Object.prototype.hasOwnProperty.call(OPERATOR_INVERSES, node.operator)) {
  75                 const operatorToken = sourceCode.getFirstTokenBetween(
  76                     node.left,
  77                     node.right,
  78                     token => token.value === node.operator
  79                 );
  80                 const text = sourceCode.getText();
  81
  82                 return text.slice(node.range[0],
  83                     operatorToken.range[0]) + OPERATOR_INVERSES[node.operator] + text.slice(operatorToken.range[1], node.range[1]);
  84             }
  85
  86             if (astUtils.getPrecedence(node) < astUtils.getPrecedence({ type: "UnaryExpression" })) {
  87                 return `!(${astUtils.getParenthesisedText(sourceCode, node)})`;
  88             }
  89             return `!${astUtils.getParenthesisedText(sourceCode, node)}`;
  90         }
  91
  92         /**
  93          * Tests if a given node always evaluates to a boolean value
  94          * @param {ASTNode} node An expression node
  95          * @returns {boolean} True if it is determined that the node will always evaluate to a boolean value
  96          */
  97         function isBooleanExpression(node) {
  98             return node.type === "BinaryExpression" && BOOLEAN_OPERATORS.has(node.operator) ||
  99                 node.type === "UnaryExpression" && node.operator === "!";
 100         }
 101
 102         /**
 103          * Test if the node matches the pattern id ? id : expression
 104          * @param {ASTNode} node The ConditionalExpression to check.
 105          * @returns {boolean} True if the pattern is matched, and false otherwise
 106          * @private
 107          */
 108         function matchesDefaultAssignment(node) {
 109             return node.test.type === "Identifier" &&
 110                    node.consequent.type === "Identifier" &&
 111                    node.test.name === node.consequent.name;
 112         }
 113
 114         return {
 115
 116             ConditionalExpression(node) {
 117                 if (isBooleanLiteral(node.alternate) && isBooleanLiteral(node.consequent)) {
 118                     context.report({
 119                         node,
 120                         loc: node.consequent.loc.start,
 121                         message: "Unnecessary use of boolean literals in conditional expression.",
 122                         fix(fixer) {
 123                             if (node.consequent.value === node.alternate.value) {
 124
 125                                 // Replace `foo ? true : true` with just `true`, but don't replace `foo() ? true : true`
 126                                 return node.test.type === "Identifier" ? fixer.replaceText(node, node.consequent.value.toString()) : null;
 127                             }
 128                             if (node.alternate.value) {
 129
 130                                 // Replace `foo() ? false : true` with `!(foo())`
 131                                 return fixer.replaceText(node, invertExpression(node.test));
 132                             }
 133
 134                             // Replace `foo ? true : false` with `foo` if `foo` is guaranteed to be a boolean, or `!!foo` otherwise.
 135
 136                             return fixer.replaceText(node, isBooleanExpression(node.test) ? astUtils.getParenthesisedText(sourceCode, node.test) : `!${invertExpression(node.test)}`);
 137                         }
 138                     });
 139                 } else if (!defaultAssignment && matchesDefaultAssignment(node)) {
 140                     context.report({
 141                         node,
 142                         loc: node.consequent.loc.start,
 143                         message: "Unnecessary use of conditional expression for default assignment.",
 144                         fix: fixer => {
 145                             const shouldParenthesizeAlternate = (
 146                                 astUtils.getPrecedence(node.alternate) < OR_PRECEDENCE &&
 147                                 !astUtils.isParenthesised(sourceCode, node.alternate)
 148                             );
 149                             const alternateText = shouldParenthesizeAlternate
 150                                 ? `(${sourceCode.getText(node.alternate)})`
 151                                 : astUtils.getParenthesisedText(sourceCode, node.alternate);
 152                             const testText = astUtils.getParenthesisedText(sourceCode, node.test);
 153
 154                             return fixer.replaceText(node, `${testText} || ${alternateText}`);
 155                         }
 156                     });
 157                 }
 158             }
 159         };
 160     }
 161 };