no-redeclare.js

/**
 * @fileoverview Rule to flag when the same variable is declared more then once.
 * @author Ilya Volodin
 */

"use strict";

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

const astUtils = require("./utils/ast-utils");

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

module.exports = {
    meta: {
        type: "suggestion",

        docs: {
            description: "disallow variable redeclaration",
            category: "Best Practices",
            recommended: true,
            url: "https://eslint.org/docs/rules/no-redeclare"
        },

        messages: {
            redeclared: "'{{id}}' is already defined.",
            redeclaredAsBuiltin: "'{{id}}' is already defined as a built-in global variable.",
            redeclaredBySyntax: "'{{id}}' is already defined by a variable declaration."
        },

        schema: [
            {
                type: "object",
                properties: {
                    builtinGlobals: { type: "boolean", default: true }
                },
                additionalProperties: false
            }
        ]
    },

    create(context) {
        const options = {
            builtinGlobals: Boolean(
                context.options.length === 0 ||
                context.options[0].builtinGlobals
            )
        };
        const sourceCode = context.getSourceCode();

        /**
         * Iterate declarations of a given variable.
         * @param {escope.variable} variable The variable object to iterate declarations.
         * @returns {IterableIterator<{type:string,node:ASTNode,loc:SourceLocation}>} The declarations.
         */
        function *iterateDeclarations(variable) {
            if (options.builtinGlobals && (
                variable.eslintImplicitGlobalSetting === "readonly" ||
                variable.eslintImplicitGlobalSetting === "writable"
            )) {
                yield { type: "builtin" };
            }

            for (const id of variable.identifiers) {
                yield { type: "syntax", node: id, loc: id.loc };
            }