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/**
* @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 };
}
if (variable.eslintExplicitGlobalComments) {
for (const comment of variable.eslintExplicitGlobalComments) {
yield {
type: "comment",
node: comment,
loc: astUtils.getNameLocationInGlobalDirectiveComment(
sourceCode,
comment,
variable.name
)
};
}
}
}
/**
* Find variables in a given scope and flag redeclared ones.
* @param {Scope} scope - An eslint-scope scope object.
* @returns {void}
* @private
*/
function findVariablesInScope(scope) {
for (const variable of scope.variables) {
const [
declaration,
...extraDeclarations
] = iterateDeclarations(variable);
if (extraDeclarations.length === 0) {
continue;
}
/*
* If the type of a declaration is different from the type of
* the first declaration, it shows the location of the first
* declaration.
*/
const detailMessageId = declaration.type === "builtin"
? "redeclaredAsBuiltin"
: "redeclaredBySyntax";
const data = { id: variable.name };
// Report extra declarations.
for (const { type, node, loc } of extraDeclarations) {
const messageId = type === declaration.type
? "redeclared"
: detailMessageId;
context.report({ node, loc, messageId, data });
}
}
}
/**
* Find variables in the current scope.
* @param {ASTNode} node The node of the current scope.
* @returns {void}
* @private
*/
function checkForBlock(node) {
const scope = context.getScope();
/*
* In ES5, some node type such as `BlockStatement` doesn't have that scope.
* `scope.block` is a different node in such a case.
*/
if (scope.block === node) {
findVariablesInScope(scope);
}
}
return {
Program() {
const scope = context.getScope();
findVariablesInScope(scope);
// Node.js or ES modules has a special scope.
if (
scope.type === "global" &&
scope.childScopes[0] &&
// The special scope's block is the Program node.
scope.block === scope.childScopes[0].block
) {
findVariablesInScope(scope.childScopes[0]);
}
},
FunctionDeclaration: checkForBlock,
FunctionExpression: checkForBlock,
ArrowFunctionExpression: checkForBlock,
BlockStatement: checkForBlock,
ForStatement: checkForBlock,
ForInStatement: checkForBlock,
ForOfStatement: checkForBlock,
SwitchStatement: checkForBlock
};
}
};
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