eslint/lib/rules/no-shadow.js

   1 /**
   2  * @fileoverview Rule to flag on declaring variables already declared in the outer scope
   3  * @author Ilya Volodin
   4  */
   5
   6 "use strict";
   7
   8 //------------------------------------------------------------------------------
   9 // Requirements
  10 //------------------------------------------------------------------------------
  11
  12 const astUtils = require("./utils/ast-utils");
  13
  14 //------------------------------------------------------------------------------
  15 // Rule Definition
  16 //------------------------------------------------------------------------------
  17
  18 module.exports = {
  19     meta: {
  20         type: "suggestion",
  21
  22         docs: {
  23             description: "disallow variable declarations from shadowing variables declared in the outer scope",
  24             category: "Variables",
  25             recommended: false,
  26             url: "https://eslint.org/docs/rules/no-shadow"
  27         },
  28
  29         schema: [
  30             {
  31                 type: "object",
  32                 properties: {
  33                     builtinGlobals: { type: "boolean", default: false },
  34                     hoist: { enum: ["all", "functions", "never"], default: "functions" },
  35                     allow: {
  36                         type: "array",
  37                         items: {
  38                             type: "string"
  39                         }
  40                     }
  41                 },
  42                 additionalProperties: false
  43             }
  44         ],
  45
  46         messages: {
  47             noShadow: "'{{name}}' is already declared in the upper scope."
  48         }
  49     },
  50
  51     create(context) {
  52
  53         const options = {
  54             builtinGlobals: context.options[0] && context.options[0].builtinGlobals,
  55             hoist: (context.options[0] && context.options[0].hoist) || "functions",
  56             allow: (context.options[0] && context.options[0].allow) || []
  57         };
  58
  59         /**
  60          * Check if variable name is allowed.
  61          * @param  {ASTNode} variable The variable to check.
  62          * @returns {boolean} Whether or not the variable name is allowed.
  63          */
  64         function isAllowed(variable) {
  65             return options.allow.indexOf(variable.name) !== -1;
  66         }
  67
  68         /**
  69          * Checks if a variable of the class name in the class scope of ClassDeclaration.
  70          *
  71          * ClassDeclaration creates two variables of its name into its outer scope and its class scope.
  72          * So we should ignore the variable in the class scope.
  73          * @param {Object} variable The variable to check.
  74          * @returns {boolean} Whether or not the variable of the class name in the class scope of ClassDeclaration.
  75          */
  76         function isDuplicatedClassNameVariable(variable) {
  77             const block = variable.scope.block;
  78
  79             return block.type === "ClassDeclaration" && block.id === variable.identifiers[0];
  80         }
  81
  82         /**
  83          * Checks if a variable is inside the initializer of scopeVar.
  84          *
  85          * To avoid reporting at declarations such as `var a = function a() {};`.
  86          * But it should report `var a = function(a) {};` or `var a = function() { function a() {} };`.
  87          * @param {Object} variable The variable to check.
  88          * @param {Object} scopeVar The scope variable to look for.
  89          * @returns {boolean} Whether or not the variable is inside initializer of scopeVar.
  90          */
  91         function isOnInitializer(variable, scopeVar) {
  92             const outerScope = scopeVar.scope;
  93             const outerDef = scopeVar.defs[0];
  94             const outer = outerDef && outerDef.parent && outerDef.parent.range;
  95             const innerScope = variable.scope;
  96             const innerDef = variable.defs[0];
  97             const inner = innerDef && innerDef.name.range;
  98
  99             return (
 100                 outer &&
 101                 inner &&
 102                 outer[0] < inner[0] &&
 103                 inner[1] < outer[1] &&
 104                 ((innerDef.type === "FunctionName" && innerDef.node.type === "FunctionExpression") || innerDef.node.type === "ClassExpression") &&
 105                 outerScope === innerScope.upper
 106             );
 107         }
 108
 109         /**
 110          * Get a range of a variable's identifier node.
 111          * @param {Object} variable The variable to get.
 112          * @returns {Array|undefined} The range of the variable's identifier node.
 113          */
 114         function getNameRange(variable) {
 115             const def = variable.defs[0];
 116
 117             return def && def.name.range;
 118         }
 119
 120         /**
 121          * Checks if a variable is in TDZ of scopeVar.
 122          * @param {Object} variable The variable to check.
 123          * @param {Object} scopeVar The variable of TDZ.
 124          * @returns {boolean} Whether or not the variable is in TDZ of scopeVar.
 125          */
 126         function isInTdz(variable, scopeVar) {
 127             const outerDef = scopeVar.defs[0];
 128             const inner = getNameRange(variable);
 129             const outer = getNameRange(scopeVar);
 130
 131             return (
 132                 inner &&
 133                 outer &&
 134                 inner[1] < outer[0] &&
 135
 136                 // Excepts FunctionDeclaration if is {"hoist":"function"}.
 137                 (options.hoist !== "functions" || !outerDef || outerDef.node.type !== "FunctionDeclaration")
 138             );
 139         }
 140
 141         /**
 142          * Checks the current context for shadowed variables.
 143          * @param {Scope} scope Fixme
 144          * @returns {void}
 145          */
 146         function checkForShadows(scope) {
 147             const variables = scope.variables;
 148
 149             for (let i = 0; i < variables.length; ++i) {
 150                 const variable = variables[i];
 151
 152                 // Skips "arguments" or variables of a class name in the class scope of ClassDeclaration.
 153                 if (variable.identifiers.length === 0 ||
 154                     isDuplicatedClassNameVariable(variable) ||
 155                     isAllowed(variable)
 156                 ) {
 157                     continue;
 158                 }
 159
 160                 // Gets shadowed variable.
 161                 const shadowed = astUtils.getVariableByName(scope.upper, variable.name);
 162
 163                 if (shadowed &&
 164                     (shadowed.identifiers.length > 0 || (options.builtinGlobals && "writeable" in shadowed)) &&
 165                     !isOnInitializer(variable, shadowed) &&
 166                     !(options.hoist !== "all" && isInTdz(variable, shadowed))
 167                 ) {
 168                     context.report({
 169                         node: variable.identifiers[0],
 170                         messageId: "noShadow",
 171                         data: variable
 172                     });
 173                 }
 174             }
 175         }
 176
 177         return {
 178             "Program:exit"() {
 179                 const globalScope = context.getScope();
 180                 const stack = globalScope.childScopes.slice();
 181
 182                 while (stack.length) {
 183                     const scope = stack.pop();
 184
 185                     stack.push(...scope.childScopes);
 186                     checkForShadows(scope);
 187                 }
 188             }
 189         };
 190
 191     }
 192 };