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Commit 557a0d2

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JoshuaKGoldbergJoshuaKGoldberg
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feat: support TypeScript syntax in no-useless-constructor (#19535)
* feat: support TypeScript syntax in no-useless-constructor * Remove unnecessary // ... * re-ran trunk fmt * git checkout main -- docs/src/_data/further_reading_links.json * touch up node.value.body check * ...as well as test newline * Add meta.dialects, meta.language
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‎docs/src/rules/no-useless-constructor.md

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@@ -77,6 +77,44 @@ class D extends A {
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:::
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This rule additionally supports TypeScript type syntax.
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Examples of **incorrect** TypeScript code for this rule:
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::: incorrect
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```ts
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/* eslint no-useless-constructor: "error" */
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class A {
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public constructor() {}
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}
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```
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:::
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Examples of **correct** TypeScript code for this rule:
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::: correct
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```ts
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/* eslint no-useless-constructor: "error" */
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class A {
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protected constructor() {}
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}
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class B extends A {
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public constructor() {
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super();
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}
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}
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class C {
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constructor(@decorated param) {}
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}
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```
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## When Not To Use It
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If you don't want to be notified about unnecessary constructors, you can safely disable this rule.

‎lib/rules/no-useless-constructor.js

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+37-1Lines changed: 37 additions & 1 deletion
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@@ -10,6 +10,35 @@ const astUtils = require("./utils/ast-utils");
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// Helpers
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//------------------------------------------------------------------------------
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/**
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* Checks whether any of a method's parameters have a decorator or are a parameter property.
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* @param {ASTNode} node A method definition node.
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* @returns {boolean} `true` if any parameter had a decorator or is a parameter property.
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*/
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function hasDecoratorsOrParameterProperty(node) {
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return node.value.params.some(
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param =>
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param.decorators?.length || param.type === "TSParameterProperty",
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);
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}
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/**
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* Checks whether a node's accessibility makes it not useless.
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* @param {ASTNode} node A method definition node.
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* @returns {boolean} `true` if the node has a useful accessibility.
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*/
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function hasUsefulAccessibility(node) {
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switch (node.accessibility) {
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case "protected":
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case "private":
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return true;
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case "public":
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return !!node.parent.parent.superClass;
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default:
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return false;
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}
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}
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/**
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* Checks whether a given array of statements is a single call of `super`.
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* @param {ASTNode[]} body An array of statements to check.
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/** @type {import('../shared/types').Rule} */
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module.exports = {
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meta: {
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dialects: ["javascript", "typescript"],
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language: "javascript",
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type: "suggestion",
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docs: {
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* @returns {void}
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*/
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function checkForConstructor(node) {
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if (node.kind !== "constructor") {
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if (
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node.kind !== "constructor" ||
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node.value.type !== "FunctionExpression" ||
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hasDecoratorsOrParameterProperty(node) ||
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hasUsefulAccessibility(node)
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) {
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return;
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}
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‎tests/lib/rules/no-useless-constructor.js

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@@ -199,3 +199,169 @@ ruleTester.run("no-useless-constructor", rule, {
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},
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],
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});
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const ruleTesterTypeScript = new RuleTester({
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languageOptions: {
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parser: require("@typescript-eslint/parser"),
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},
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});
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ruleTesterTypeScript.run("no-useless-constructor", rule, {
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valid: [
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`
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declare class A {
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constructor();
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}
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`,
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`
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class A {
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constructor();
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}
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`,
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`
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abstract class A {
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constructor();
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}
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`,
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`
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class A {
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constructor(private name: string) {}
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}
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`,
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`
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class A {
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constructor(public name: string) {}
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}
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`,
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`
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class A {
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constructor(protected name: string) {}
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}
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`,
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`
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class A {
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private constructor() {}
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}
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`,
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`
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class A {
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protected constructor() {}
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}
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`,
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`
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class A extends B {
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public constructor() {}
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}
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`,
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`
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class A extends B {
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public constructor() {
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super();
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}
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}
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`,
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`
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class A extends B {
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protected constructor(foo, bar) {
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super(bar);
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}
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}
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`,
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`
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class A extends B {
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private constructor(foo, bar) {
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super(bar);
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}
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}
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`,
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`
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class A extends B {
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public constructor(foo) {
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super(foo);
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}
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}
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`,
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`
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class A extends B {
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public constructor(foo) {}
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}
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`,
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`
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class A {
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constructor(foo);
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}
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`,
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`
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class A {
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constructor(@Foo foo) {}
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}
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`,
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`
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class A {
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constructor(@Foo foo: string) {}
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}
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`,
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`
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class A extends Object {
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constructor(@Foo foo: string) {
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super(foo);
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}
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}
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`,
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`
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class A extends Object {
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constructor(foo: string, @Bar() bar) {
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super(foo, bar);
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}
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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: `
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class A {
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constructor() {}
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}
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`,
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errors: [
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{
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messageId: "noUselessConstructor",
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suggestions: [
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{
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messageId: "removeConstructor",
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output: `
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class A {
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${" "}
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}
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`,
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},
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],
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type: "MethodDefinition",
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},
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],
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},
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{
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code: `
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class A {
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public constructor() {}
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}
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`,
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errors: [
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{
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messageId: "noUselessConstructor",
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suggestions: [
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{
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messageId: "removeConstructor",
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output: `
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class A {
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${" "}
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}
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`,
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},
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],
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type: "MethodDefinition",
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},
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],
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},
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],
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});

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