/**
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* @fileoverview Rule to flag when the same variable is declared more then once.
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* @author Ilya Volodin
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Requirements
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//------------------------------------------------------------------------------
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const astUtils = require("./utils/ast-utils");
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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type: "suggestion",
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docs: {
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description: "disallow variable redeclaration",
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category: "Best Practices",
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recommended: true,
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url: "https://eslint.org/docs/rules/no-redeclare"
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},
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messages: {
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redeclared: "'{{id}}' is already defined.",
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redeclaredAsBuiltin: "'{{id}}' is already defined as a built-in global variable.",
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redeclaredBySyntax: "'{{id}}' is already defined by a variable declaration."
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},
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schema: [
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{
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type: "object",
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properties: {
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builtinGlobals: { type: "boolean", default: true }
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},
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additionalProperties: false
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}
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]
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},
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create(context) {
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const options = {
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builtinGlobals: Boolean(
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context.options.length === 0 ||
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context.options[0].builtinGlobals
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)
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};
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const sourceCode = context.getSourceCode();
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/**
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* Iterate declarations of a given variable.
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* @param {escope.variable} variable The variable object to iterate declarations.
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* @returns {IterableIterator<{type:string,node:ASTNode,loc:SourceLocation}>} The declarations.
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*/
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function *iterateDeclarations(variable) {
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if (options.builtinGlobals && (
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variable.eslintImplicitGlobalSetting === "readonly" ||
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variable.eslintImplicitGlobalSetting === "writable"
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)) {
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yield { type: "builtin" };
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}
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for (const id of variable.identifiers) {
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yield { type: "syntax", node: id, loc: id.loc };
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}
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if (variable.eslintExplicitGlobalComments) {
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for (const comment of variable.eslintExplicitGlobalComments) {
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yield {
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type: "comment",
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node: comment,
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loc: astUtils.getNameLocationInGlobalDirectiveComment(
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sourceCode,
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comment,
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variable.name
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)
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};
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}
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}
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}
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/**
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* Find variables in a given scope and flag redeclared ones.
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* @param {Scope} scope - An eslint-scope scope object.
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* @returns {void}
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* @private
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*/
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function findVariablesInScope(scope) {
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for (const variable of scope.variables) {
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const [
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declaration,
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...extraDeclarations
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] = iterateDeclarations(variable);
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if (extraDeclarations.length === 0) {
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continue;
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}
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/*
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* If the type of a declaration is different from the type of
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* the first declaration, it shows the location of the first
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* declaration.
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*/
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const detailMessageId = declaration.type === "builtin"
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? "redeclaredAsBuiltin"
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: "redeclaredBySyntax";
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const data = { id: variable.name };
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// Report extra declarations.
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for (const { type, node, loc } of extraDeclarations) {
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const messageId = type === declaration.type
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? "redeclared"
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: detailMessageId;
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context.report({ node, loc, messageId, data });
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}
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}
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}
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/**
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* Find variables in the current scope.
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* @param {ASTNode} node The node of the current scope.
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* @returns {void}
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* @private
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*/
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function checkForBlock(node) {
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const scope = context.getScope();
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/*
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* In ES5, some node type such as `BlockStatement` doesn't have that scope.
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* `scope.block` is a different node in such a case.
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*/
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if (scope.block === node) {
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findVariablesInScope(scope);
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}
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}
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return {
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Program() {
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const scope = context.getScope();
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findVariablesInScope(scope);
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// Node.js or ES modules has a special scope.
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if (
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scope.type === "global" &&
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scope.childScopes[0] &&
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// The special scope's block is the Program node.
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scope.block === scope.childScopes[0].block
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) {
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findVariablesInScope(scope.childScopes[0]);
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}
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},
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FunctionDeclaration: checkForBlock,
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FunctionExpression: checkForBlock,
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ArrowFunctionExpression: checkForBlock,
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BlockStatement: checkForBlock,
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ForStatement: checkForBlock,
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ForInStatement: checkForBlock,
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ForOfStatement: checkForBlock,
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SwitchStatement: checkForBlock
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};
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}
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};
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