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feat(eslint-plugin): add no-duplicate-type-constituents rule (typescript-eslint#5728)
* feat: add rule code * test: add test for rule * docs: add docs of new rule * refactor: make method definitions more concise * fix: change check option to ignore option * refactor: rename to type-constituents * refactor: use recursive type-node checker * fix: rename doc filename and test title * refactor: use removeRage instead of replaceText * refactor: narrows node comparison function argument type * fix: doc description * refactor: update hasComments logic * fix: remove cases that never occur * refactor: use type checker * fix: do not change fixer behavior with comments * fix: delete bracket with fixer * fix: fix test cases and meta data * refactor : also use ast node checker * refactor : organize test cases * fix: fix rule description * fix: modify Rule Details to match implementation * refactor: add uniq set in each case * refactor: delete type guard * refactor: add test case * refactor: delete unnecessary comparison logic * refactor: add test-case * feat: show which the previous type is duplicating * fix: use word constituents * fix: sample case * fix: lint message * fix: rule docs * fix: use === & !== * fix: No `noFormat` in test. * fix: correct examples * refactor: use `flatMap` * refactor: Do not use temporary `fixes` variable. * refactor: make type comparison lazy and use cache * refactor: no unnecessary loop in `fix` function. * refactor: get logic of tokens to be deleted * refactor: separate report function and solve fixer range problem * refactor: improved documentation. * fix: make additionalProperties false * fix: delete printing message {{duplicated}} * fix: do not abbreviate "unique" * refactor: reverse the key and value in cachedTypeMap to reduce the amount of calculation. * fix: reportLocation start * refactor: stop test generation and write tests naively. * refactor: Narrowing the type of options * Revert "refactor: Narrowing the type of options" This reverts commit a6b2382. * refactor: use Set instead of array
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‎packages/eslint-plugin/docs/rules/no-duplicate-type-constituents.md

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---
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description: 'Disallow duplicate constituents of union or intersection types.'
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---
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> 🛑 This file is source code, not the primary documentation location! 🛑
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>
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> See **https://typescript-eslint.io/rules/no-duplicate-type-constituents** for documentation.
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TypeScript supports types ("constituents") within union and intersection types being duplicates of each other.
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However, developers typically expect each constituent to be unique within its intersection or union.
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Duplicate values make the code overly verbose and generally reduce readability.
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## Rule Details
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This rule disallows duplicate union or intersection constituents.
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We consider types to be duplicate if they evaluate to the same result in the type system.
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For example, given `type A = string` and `type T = string | A`, this rule would flag that `A` is the same type as `string`.
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<!--tabs-->
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### ❌ Incorrect
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```ts
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type T1 = 'A' | 'A';
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type T2 = A | A | B;
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type T3 = { a: string } & { a: string };
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type T4 = [1, 2, 3] | [1, 2, 3];
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type StringA = string;
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type StringB = string;
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type T5 = StringA | StringB;
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```
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### ✅ Correct
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```ts
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type T1 = 'A' | 'B';
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type T2 = A | B | C;
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type T3 = { a: string } & { b: string };
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type T4 = [1, 2, 3] | [1, 2, 3, 4];
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type StringA = string;
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type NumberB = number;
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type T5 = StringA | NumberB;
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```
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## Options
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### `ignoreIntersections`
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When set to true, duplicate checks on intersection type constituents are ignored.
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### `ignoreUnions`
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When set to true, duplicate checks on union type constituents are ignored.

‎packages/eslint-plugin/src/configs/all.ts

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'no-dupe-class-members': 'off',
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'@typescript-eslint/no-dupe-class-members': 'error',
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'@typescript-eslint/no-duplicate-enum-values': 'error',
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'@typescript-eslint/no-duplicate-type-constituents': 'error',
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'@typescript-eslint/no-dynamic-delete': 'error',
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'no-empty-function': 'off',
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'@typescript-eslint/no-empty-function': 'error',

‎packages/eslint-plugin/src/rules/index.ts

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@@ -38,6 +38,7 @@ import noConfusingVoidExpression from './no-confusing-void-expression';
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import noDupeClassMembers from './no-dupe-class-members';
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import noDuplicateEnumValues from './no-duplicate-enum-values';
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import noDuplicateImports from './no-duplicate-imports';
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import noDuplicateTypeConstituents from './no-duplicate-type-constituents';
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import noDynamicDelete from './no-dynamic-delete';
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import noEmptyFunction from './no-empty-function';
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import noEmptyInterface from './no-empty-interface';
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'no-dupe-class-members': noDupeClassMembers,
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'no-duplicate-enum-values': noDuplicateEnumValues,
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'no-duplicate-imports': noDuplicateImports,
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'no-duplicate-type-constituents': noDuplicateTypeConstituents,
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'no-dynamic-delete': noDynamicDelete,
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'no-empty-function': noEmptyFunction,
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'no-empty-interface': noEmptyInterface,

‎packages/eslint-plugin/src/rules/no-duplicate-type-constituents.ts

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import type { TSESTree } from '@typescript-eslint/utils';
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import { AST_NODE_TYPES } from '@typescript-eslint/utils';
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import type { Type } from 'typescript';
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import * as util from '../util';
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export type Options = [
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{
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ignoreIntersections?: boolean;
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ignoreUnions?: boolean;
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},
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];
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export type MessageIds = 'duplicate';
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const astIgnoreKeys = new Set(['range', 'loc', 'parent']);
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const isSameAstNode = (actualNode: unknown, expectedNode: unknown): boolean => {
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if (actualNode === expectedNode) {
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return true;
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}
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if (
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actualNode &&
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expectedNode &&
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typeof actualNode === 'object' &&
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typeof expectedNode === 'object'
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) {
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if (Array.isArray(actualNode) && Array.isArray(expectedNode)) {
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if (actualNode.length !== expectedNode.length) {
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return false;
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}
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return !actualNode.some(
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(nodeEle, index) => !isSameAstNode(nodeEle, expectedNode[index]),
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);
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}
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const actualNodeKeys = Object.keys(actualNode).filter(
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key => !astIgnoreKeys.has(key),
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);
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const expectedNodeKeys = Object.keys(expectedNode).filter(
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key => !astIgnoreKeys.has(key),
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);
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if (actualNodeKeys.length !== expectedNodeKeys.length) {
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return false;
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}
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if (
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actualNodeKeys.some(
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actualNodeKey =>
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!Object.prototype.hasOwnProperty.call(expectedNode, actualNodeKey),
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)
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) {
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return false;
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}
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if (
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actualNodeKeys.some(
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actualNodeKey =>
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!isSameAstNode(
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actualNode[actualNodeKey as keyof typeof actualNode],
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expectedNode[actualNodeKey as keyof typeof expectedNode],
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),
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)
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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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return false;
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};
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export default util.createRule<Options, MessageIds>({
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name: 'no-duplicate-type-constituents',
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meta: {
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type: 'suggestion',
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docs: {
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description:
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'Disallow duplicate constituents of union or intersection types',
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recommended: false,
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requiresTypeChecking: true,
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},
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fixable: 'code',
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messages: {
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duplicate: '{{type}} type constituent is duplicated with {{previous}}.',
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},
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schema: [
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{
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additionalProperties: false,
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type: 'object',
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properties: {
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ignoreIntersections: {
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type: 'boolean',
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},
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ignoreUnions: {
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type: 'boolean',
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},
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},
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},
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],
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},
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defaultOptions: [
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{
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ignoreIntersections: false,
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ignoreUnions: false,
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},
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],
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create(context, [{ ignoreIntersections, ignoreUnions }]) {
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const parserServices = util.getParserServices(context);
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const checker = parserServices.program.getTypeChecker();
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function checkDuplicate(
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node: TSESTree.TSIntersectionType | TSESTree.TSUnionType,
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): void {
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const cachedTypeMap: Map<Type, TSESTree.TypeNode> = new Map();
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node.types.reduce<TSESTree.TypeNode[]>(
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(uniqueConstituents, constituentNode) => {
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const duplicatedPreviousConstituentInAst = uniqueConstituents.find(
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ele => isSameAstNode(ele, constituentNode),
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);
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if (duplicatedPreviousConstituentInAst) {
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reportDuplicate(
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{
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duplicated: constituentNode,
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duplicatePrevious: duplicatedPreviousConstituentInAst,
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},
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node,
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);
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return uniqueConstituents;
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}
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const constituentNodeType = checker.getTypeAtLocation(
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parserServices.esTreeNodeToTSNodeMap.get(constituentNode),
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);
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const duplicatedPreviousConstituentInType =
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cachedTypeMap.get(constituentNodeType);
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if (duplicatedPreviousConstituentInType) {
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reportDuplicate(
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{
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duplicated: constituentNode,
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duplicatePrevious: duplicatedPreviousConstituentInType,
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},
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node,
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);
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return uniqueConstituents;
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}
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cachedTypeMap.set(constituentNodeType, constituentNode);
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return [...uniqueConstituents, constituentNode];
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},
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[],
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);
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}
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function reportDuplicate(
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duplicateConstituent: {
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duplicated: TSESTree.TypeNode;
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duplicatePrevious: TSESTree.TypeNode;
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},
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parentNode: TSESTree.TSIntersectionType | TSESTree.TSUnionType,
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): void {
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const sourceCode = context.getSourceCode();
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const beforeTokens = sourceCode.getTokensBefore(
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duplicateConstituent.duplicated,
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{ filter: token => token.value === '|' || token.value === '&' },
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);
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const beforeUnionOrIntersectionToken =
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beforeTokens[beforeTokens.length - 1];
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const bracketBeforeTokens = sourceCode.getTokensBetween(
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beforeUnionOrIntersectionToken,
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duplicateConstituent.duplicated,
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);
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const bracketAfterTokens = sourceCode.getTokensAfter(
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duplicateConstituent.duplicated,
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{ count: bracketBeforeTokens.length },
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);
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const reportLocation: TSESTree.SourceLocation = {
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start: duplicateConstituent.duplicated.loc.start,
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end:
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bracketAfterTokens.length > 0
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? bracketAfterTokens[bracketAfterTokens.length - 1].loc.end
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: duplicateConstituent.duplicated.loc.end,
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};
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context.report({
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data: {
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type:
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parentNode.type === AST_NODE_TYPES.TSIntersectionType
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? 'Intersection'
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: 'Union',
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previous: sourceCode.getText(duplicateConstituent.duplicatePrevious),
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},
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messageId: 'duplicate',
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node: duplicateConstituent.duplicated,
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loc: reportLocation,
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fix: fixer => {
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return [
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beforeUnionOrIntersectionToken,
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...bracketBeforeTokens,
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duplicateConstituent.duplicated,
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...bracketAfterTokens,
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].map(token => fixer.remove(token));
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},
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});
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}
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return {
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...(!ignoreIntersections && {
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TSIntersectionType: checkDuplicate,
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}),
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...(!ignoreUnions && {
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TSUnionType: checkDuplicate,
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}),
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};
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},
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});

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