node/tools/eslint/lib/rules/no-shadow.js

/**
 * @fileoverview Rule to flag on declaring variables already declared in the outer scope
 * @author Ilya Volodin
 * @copyright 2013 Ilya Volodin. All rights reserved.
 */

"use strict";

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

module.exports = function(context) {

    /**
     * Checks if a variable is contained in the list of given scope variables.
     * @param {Object} variable The variable to check.
     * @param {Array} scopeVars The scope variables to look for.
     * @returns {boolean} Whether or not the variable is contains in the list of scope variables.
     */
    function isContainedInScopeVars(variable, scopeVars) {
        return scopeVars.some(function (scopeVar) {
            if (scopeVar.identifiers.length > 0) {
                return variable.name === scopeVar.name;
            }
            return false;
        });
    }

    /**
     * Checks if the given variables are shadowed in the given scope.
     * @param {Array} variables The variables to look for
     * @param {Object} scope The scope to be checked.
     * @returns {void}
     */
    function checkShadowsInScope(variables, scope) {
        variables.forEach(function (variable) {
            if (isContainedInScopeVars(variable, scope.variables) &&
                    // "arguments" is a special case that has no identifiers (#1759)
                    variable.identifiers.length > 0 &&

                    // function names are exempt
                    variable.defs.length && variable.defs[0].type !== "FunctionName"
            ) {
                context.report(variable.identifiers[0], "{{a}} is already declared in the upper scope.", {a: variable.name});
            }
        });
    }

    /**
     * Checks the current context for shadowed variables.
     * @returns {void}
     */
    function checkForShadows() {
        var scope = context.getScope(),
            variables = scope.variables;

        // iterate through the array of variables and find duplicates with the upper scope
        var upper = scope.upper;
        while (upper) {
            checkShadowsInScope(variables, upper);
            upper = upper.upper;
        }
    }

    return {
        "FunctionDeclaration": checkForShadows,
        "FunctionExpression": checkForShadows,
        "ArrowFunctionExpression": checkForShadows
    };

};