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348 lines
11 KiB
348 lines
11 KiB
/**
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* @fileoverview Rule to flag use of variables before they are defined
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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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// Helpers
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//------------------------------------------------------------------------------
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const SENTINEL_TYPE = /^(?:(?:Function|Class)(?:Declaration|Expression)|ArrowFunctionExpression|CatchClause|ImportDeclaration|ExportNamedDeclaration)$/u;
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const FOR_IN_OF_TYPE = /^For(?:In|Of)Statement$/u;
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/**
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* Parses a given value as options.
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* @param {any} options A value to parse.
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* @returns {Object} The parsed options.
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*/
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function parseOptions(options) {
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let functions = true;
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let classes = true;
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let variables = true;
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let allowNamedExports = false;
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if (typeof options === "string") {
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functions = (options !== "nofunc");
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} else if (typeof options === "object" && options !== null) {
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functions = options.functions !== false;
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classes = options.classes !== false;
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variables = options.variables !== false;
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allowNamedExports = !!options.allowNamedExports;
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}
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return { functions, classes, variables, allowNamedExports };
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}
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/**
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* Checks whether or not a given location is inside of the range of a given node.
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* @param {ASTNode} node An node to check.
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* @param {number} location A location to check.
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* @returns {boolean} `true` if the location is inside of the range of the node.
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*/
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function isInRange(node, location) {
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return node && node.range[0] <= location && location <= node.range[1];
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}
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/**
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* Checks whether or not a given location is inside of the range of a class static initializer.
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* Static initializers are static blocks and initializers of static fields.
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* @param {ASTNode} node `ClassBody` node to check static initializers.
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* @param {number} location A location to check.
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* @returns {boolean} `true` if the location is inside of a class static initializer.
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*/
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function isInClassStaticInitializerRange(node, location) {
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return node.body.some(classMember => (
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(
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classMember.type === "StaticBlock" &&
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isInRange(classMember, location)
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) ||
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(
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classMember.type === "PropertyDefinition" &&
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classMember.static &&
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classMember.value &&
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isInRange(classMember.value, location)
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)
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));
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}
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/**
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* Checks whether a given scope is the scope of a class static initializer.
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* Static initializers are static blocks and initializers of static fields.
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* @param {eslint-scope.Scope} scope A scope to check.
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* @returns {boolean} `true` if the scope is a class static initializer scope.
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*/
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function isClassStaticInitializerScope(scope) {
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if (scope.type === "class-static-block") {
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return true;
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}
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if (scope.type === "class-field-initializer") {
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// `scope.block` is PropertyDefinition#value node
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const propertyDefinition = scope.block.parent;
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return propertyDefinition.static;
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}
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return false;
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}
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/**
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* Checks whether a given reference is evaluated in an execution context
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* that isn't the one where the variable it refers to is defined.
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* Execution contexts are:
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* - top-level
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* - functions
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* - class field initializers (implicit functions)
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* - class static blocks (implicit functions)
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* Static class field initializers and class static blocks are automatically run during the class definition evaluation,
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* and therefore we'll consider them as a part of the parent execution context.
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* Example:
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*
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* const x = 1;
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*
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* x; // returns `false`
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* () => x; // returns `true`
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*
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* class C {
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* field = x; // returns `true`
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* static field = x; // returns `false`
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*
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* method() {
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* x; // returns `true`
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* }
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*
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* static method() {
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* x; // returns `true`
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* }
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*
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* static {
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* x; // returns `false`
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* }
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* }
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* @param {eslint-scope.Reference} reference A reference to check.
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* @returns {boolean} `true` if the reference is from a separate execution context.
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*/
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function isFromSeparateExecutionContext(reference) {
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const variable = reference.resolved;
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let scope = reference.from;
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// Scope#variableScope represents execution context
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while (variable.scope.variableScope !== scope.variableScope) {
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if (isClassStaticInitializerScope(scope.variableScope)) {
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scope = scope.variableScope.upper;
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} else {
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return true;
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}
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}
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return false;
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}
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/**
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* Checks whether or not a given reference is evaluated during the initialization of its variable.
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*
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* This returns `true` in the following cases:
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*
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* var a = a
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* var [a = a] = list
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* var {a = a} = obj
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* for (var a in a) {}
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* for (var a of a) {}
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* var C = class { [C]; };
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* var C = class { static foo = C; };
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* var C = class { static { foo = C; } };
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* class C extends C {}
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* class C extends (class { static foo = C; }) {}
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* class C { [C]; }
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* @param {Reference} reference A reference to check.
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* @returns {boolean} `true` if the reference is evaluated during the initialization.
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*/
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function isEvaluatedDuringInitialization(reference) {
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if (isFromSeparateExecutionContext(reference)) {
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/*
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* Even if the reference appears in the initializer, it isn't evaluated during the initialization.
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* For example, `const x = () => x;` is valid.
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*/
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return false;
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}
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const location = reference.identifier.range[1];
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const definition = reference.resolved.defs[0];
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if (definition.type === "ClassName") {
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// `ClassDeclaration` or `ClassExpression`
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const classDefinition = definition.node;
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return (
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isInRange(classDefinition, location) &&
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/*
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* Class binding is initialized before running static initializers.
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* For example, `class C { static foo = C; static { bar = C; } }` is valid.
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*/
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!isInClassStaticInitializerRange(classDefinition.body, location)
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);
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}
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let node = definition.name.parent;
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while (node) {
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if (node.type === "VariableDeclarator") {
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if (isInRange(node.init, location)) {
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return true;
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}
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if (FOR_IN_OF_TYPE.test(node.parent.parent.type) &&
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isInRange(node.parent.parent.right, location)
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) {
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return true;
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}
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break;
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} else if (node.type === "AssignmentPattern") {
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if (isInRange(node.right, location)) {
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return true;
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}
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} else if (SENTINEL_TYPE.test(node.type)) {
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break;
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}
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node = node.parent;
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}
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return false;
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}
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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/** @type {import('../shared/types').Rule} */
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module.exports = {
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meta: {
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type: "problem",
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docs: {
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description: "Disallow the use of variables before they are defined",
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recommended: false,
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url: "https://eslint.org/docs/latest/rules/no-use-before-define"
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},
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schema: [
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{
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oneOf: [
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{
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enum: ["nofunc"]
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},
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{
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type: "object",
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properties: {
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functions: { type: "boolean" },
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classes: { type: "boolean" },
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variables: { type: "boolean" },
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allowNamedExports: { type: "boolean" }
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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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],
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messages: {
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usedBeforeDefined: "'{{name}}' was used before it was defined."
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}
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},
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create(context) {
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const options = parseOptions(context.options[0]);
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const sourceCode = context.sourceCode;
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/**
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* Determines whether a given reference should be checked.
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*
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* Returns `false` if the reference is:
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* - initialization's (e.g., `let a = 1`).
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* - referring to an undefined variable (i.e., if it's an unresolved reference).
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* - referring to a variable that is defined, but not in the given source code
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* (e.g., global environment variable or `arguments` in functions).
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* - allowed by options.
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* @param {eslint-scope.Reference} reference The reference
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* @returns {boolean} `true` if the reference should be checked
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*/
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function shouldCheck(reference) {
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if (reference.init) {
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return false;
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}
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const { identifier } = reference;
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if (
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options.allowNamedExports &&
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identifier.parent.type === "ExportSpecifier" &&
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identifier.parent.local === identifier
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) {
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return false;
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}
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const variable = reference.resolved;
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if (!variable || variable.defs.length === 0) {
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return false;
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}
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const definitionType = variable.defs[0].type;
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if (!options.functions && definitionType === "FunctionName") {
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return false;
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}
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if (
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(
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!options.variables && definitionType === "Variable" ||
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!options.classes && definitionType === "ClassName"
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) &&
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// don't skip checking the reference if it's in the same execution context, because of TDZ
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isFromSeparateExecutionContext(reference)
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) {
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return false;
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}
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return true;
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}
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/**
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* Finds and validates all references in a given scope and its child scopes.
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* @param {eslint-scope.Scope} scope The scope object.
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* @returns {void}
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*/
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function checkReferencesInScope(scope) {
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scope.references.filter(shouldCheck).forEach(reference => {
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const variable = reference.resolved;
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const definitionIdentifier = variable.defs[0].name;
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if (
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reference.identifier.range[1] < definitionIdentifier.range[1] ||
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isEvaluatedDuringInitialization(reference)
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) {
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context.report({
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node: reference.identifier,
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messageId: "usedBeforeDefined",
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data: reference.identifier
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});
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}
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});
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scope.childScopes.forEach(checkReferencesInScope);
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}
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return {
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Program(node) {
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checkReferencesInScope(sourceCode.getScope(node));
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}
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};
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}
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};
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