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Rule S1821: "switch" statements should not be nested (#241)
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‎README.md‎

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@@ -30,6 +30,7 @@ Code Smells, or maintainability issues, are raised for places of code which migh
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* Two branches in a conditional structure should not have exactly the same implementation ([`no-duplicated-branches`])
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* Functions should not have identical implementations ([`no-identical-functions`])
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* Boolean checks should not be inverted ([`no-inverted-boolean-check`]) (:wrench: *fixable*)
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* "switch" statements should not be nested ([`no-nested-switch`])
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* Template literals should not be nested ([`no-nested-template-literals`])
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* Boolean literals should not be redundant ([`no-redundant-boolean`])
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* Jump statements should not be redundant ([`no-redundant-jump`])
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[`no-identical-expressions`]: ./docs/rules/no-identical-expressions.md
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[`no-identical-functions`]: ./docs/rules/no-identical-functions.md
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[`no-inverted-boolean-check`]: ./docs/rules/no-inverted-boolean-check.md
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[`no-nested-switch`]: ./docs/rules/no-nested-switch.md
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[`no-nested-template-literals`]: ./docs/rules/no-nested-template-literals.md
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[`no-one-iteration-loop`]: ./docs/rules/no-one-iteration-loop.md
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[`no-redundant-boolean`]: ./docs/rules/no-redundant-boolean.md

‎docs/rules/no-nested-switch.md‎

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# no-nested-switch
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Nested `switch` structures are difficult to understand because you can easily confuse the cases of an inner `switch` as belonging to an outer statement. Therefore nested `switch` statements should be avoided.
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Specifically, you should structure your code to avoid the need for nested `switch` statements, but if you cannot, then consider moving the inner `switch` to another function.
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## Noncompliant Code Example
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```javascript
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function foo(n, m) {
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switch (n) {
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case 0:
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switch (m) { // Noncompliant; nested switch
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// ...
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}
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case 1:
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// ...
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default:
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// ...
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}
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}
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```
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## Compliant Solution
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```javascript
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function foo(n, m) {
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switch (n) {
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case 0:
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bar(m);
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case 1:
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// ...
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default:
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// ...
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}
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}
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function bar(m) {
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switch(m) {
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// ...
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}
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}
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```

‎ruling/snapshots/no-nested-switch‎

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src/react-native/Libraries/Renderer/ReactFabric-dev.js: 3913,9895,10737,10758
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src/react-native/Libraries/Renderer/ReactFabric-prod.js: 1452,3961
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src/react-native/Libraries/Renderer/ReactNativeRenderer-dev.js: 4292,10265,11107,11128
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src/react-native/Libraries/Renderer/ReactNativeRenderer-prod.js: 1668,4454
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src/react/packages/react-is/src/ReactIs.js: 32,40
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src/react/packages/react-reconciler/src/ReactFiber.js: 354
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src/react/packages/react-reconciler/src/ReactFiberCommitWork.js: 263
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src/react/packages/react-reconciler/src/ReactFiberHydrationContext.js: 140,161
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src/react/packages/react/src/ReactChildren.js: 124
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src/react/scripts/rollup/forks.js: 44,96
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src/react/scripts/rollup/packaging.js: 46

‎src/index.ts‎

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@@ -34,6 +34,7 @@ const sonarjsRules: [string, TSESLint.Linter.RuleLevel][] = [
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['no-identical-functions', 'error'],
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['no-identical-expressions', 'error'],
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['no-inverted-boolean-check', 'error'],
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['no-nested-switch', 'error'],
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['no-nested-template-literals', 'error'],
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['no-one-iteration-loop', 'error'],
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['no-redundant-boolean', 'error'],

‎src/rules/no-nested-switch.ts‎

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/*
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* eslint-plugin-sonarjs
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* Copyright (C) 2018-2021 SonarSource SA
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 3 of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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// https://jira.sonarsource.com/browse/RSPEC-1821
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import { TSESTree } from '@typescript-eslint/experimental-utils';
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import { Rule } from '../utils/types';
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const message = 'Refactor the code to eliminate this nested "switch".';
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const rule: Rule.RuleModule = {
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meta: {
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type: 'suggestion',
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},
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create(context: Rule.RuleContext) {
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return {
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'SwitchStatement SwitchStatement': (node: TSESTree.Node) => {
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const switchToken = context
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.getSourceCode()
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.getFirstToken(node, token => token.value === 'switch');
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context.report({
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message,
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loc: switchToken!.loc,
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});
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},
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};
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},
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};
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export = rule;

‎tests/rules/no-nested-switch.test.ts‎

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/*
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* eslint-plugin-sonarjs
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* Copyright (C) 2018-2021 SonarSource SA
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 3 of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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import { ruleTester } from '../rule-tester';
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import * as rule from '../../src/rules/no-nested-switch';
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const MESSAGE = 'Refactor the code to eliminate this nested "switch".';
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ruleTester.run('switch statements should not be nested', rule, {
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valid: [
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{
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code: `switch (x) {
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case 1: a; break;
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default: b;
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};`,
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},
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],
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invalid: [
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{
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code: `switch (x) {
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case 1: a; break;
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case 2:
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switch (y) {
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case 3: c; break;
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default: d;
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};
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break;
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default: b;
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}`,
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errors: [
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{
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message: MESSAGE,
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line: 4,
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endLine: 4,
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column: 11,
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endColumn: 17,
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},
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],
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},
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{
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code: `switch (x) {
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case 1: a; break;
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case 2: {
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switch (y) {
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case 3: c; break;
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default: d;
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};
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switch (z) {
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case 3: c; break;
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default: d;
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};
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break;
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}
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default: b;
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}`,
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errors: [
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{
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message: MESSAGE,
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line: 4,
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endLine: 4,
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column: 15,
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endColumn: 21,
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},
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{
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message: MESSAGE,
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line: 8,
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endLine: 8,
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column: 15,
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endColumn: 21,
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},
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],
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},
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{
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code: `switch (x) {
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case 1: a; break;
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case 2:
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switch (y) {
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case 3: c;
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default:
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switch (z) {
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case 4: d; break;
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default: e;
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}
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}
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break;
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default: b;
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}`,
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errors: [
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{
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message: MESSAGE,
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line: 4,
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endLine: 4,
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column: 15,
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endColumn: 21,
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},
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{
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message: MESSAGE,
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line: 7,
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endLine: 7,
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column: 19,
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endColumn: 25,
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},
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],
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},
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{
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code: `switch (x) {
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case 1: a;
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case 2: b;
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default:
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switch (y) {
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case 3: c;
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default: d;
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}
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}`,
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errors: [
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{
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message: MESSAGE,
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line: 5,
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endLine: 5,
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column: 15,
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endColumn: 21,
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},
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],
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},
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{
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code: `switch (x) {
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case 1:
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let isideFunction = () => {
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switch (y) {}
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}
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}`,
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errors: [
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{
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message: MESSAGE,
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line: 4,
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endLine: 4,
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column: 17,
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endColumn: 23,
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},
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],
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},
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],
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});

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