[@typescript-eslint/no-unused-vars] False positive for an interface used as a generic parameter on a function with a decorator. #2961

timecatalyst · 2021-01-21T19:01:41Z

Sorry, I know a lot of similar issues like this have been reported, but none of them appear to address my specific problem. I'm working in a fresh NestJS project (generated using @nestjs/cli) and for some reason the @Get() decorator is causing the linter to flag an interface as being unused.

I had originally reported the issue on the NestJS repo, but they suggested it may be a linter problem and to ask about it here (See my comment near the bottom: nestjs/nest#4684). I accept the possibility that I might just have something wrong in my configuration, but I can't for the life of me figure out what that may be.

I have tried restarting my IDE and the issue persists.
I have updated to the latest version of the packages.
I have read the FAQ and my problem is not listed.

Repro

{
  "rules": {
    "@typescript-eslint/interface-name-prefix": "off",
    "@typescript-eslint/explicit-function-return-type": "off",
    "@typescript-eslint/explicit-module-boundary-types": "off",
    "@typescript-eslint/no-explicit-any": "off",
  },
};

As I mentioned earlier, this is a brand new project generated freshly from the NestJS CLI. The only upgrade the @typescript-eslint libraries to the latest versions.

The linter generates a warning on the interface Foo at line 3, despite its use at line 10.

If I remove the @Get() decorator, or rewrite doSomething() to not use a Promise<>, the warning goes away.

 1 import { Controller, Get } from '@nestjs/common';
 2
 3 interface Foo {
 4   foo: string;
 5 }
 6
 7 @Controller('foo') 
 8 export class FooController {
 9   @Get()
10   async doSomething(): Promise<Foo> {
11     return Promise.resolve({ foo: 'bar' });
12   }
13 }

tsconfig.json:

{
  "compilerOptions": {
    "module": "commonjs",
    "declaration": true,
    "removeComments": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "allowSyntheticDefaultImports": true,
    "target": "es2017",
    "sourceMap": true,
    "outDir": "./dist",
    "baseUrl": "./",
    "incremental": true
  }
}

Expected Result

No warning should occur.

Actual Result

ESLint: 'Foo' is defined but never used.(@typescript-eslint/no-unused-vars)

Additional Info

None

Versions

package	version
`@typescript-eslint/eslint-plugin`	`4.14.0`
`@typescript-eslint/parser`	`4.14.0`
`TypeScript`	`4.0.5`
`ESLint`	`7.12.1`
`node`	`12.8.3`

The text was updated successfully, but these errors were encountered:

bradzacher · 2021-01-21T19:03:15Z

Same as #2941, #2942, #2945, #2947, #2950, #2957

timecatalyst · 2021-01-25T20:21:27Z

Sorry, but I'm still seeing the same problem after upgrading my libraries to v4.14.1. Same reproduction steps as before, a class method decorator combined with a generic return type. Here's a more minimalistic version that removes NestJS from the equation:

 1 interface Foo {
 2   foo: string;
 3 }
 4
 5 function MyDecorator() {
 6   return (target, propertyKey: string, descriptor: PropertyDescriptor) =>
 7     console.log('MyDecorator(): called');
 8 }
 9
10 export class FooController {
11   @MyDecorator()
12   async doSomething(): Promise<Foo> {
13     return Promise.resolve({ foo: 'foo' });
14   }
15 }

bradzacher · 2021-01-25T20:24:01Z

Nuke your node modules and reinstall.
Also restart your IDE.

This is fixed (I just tested your code against master)

timecatalyst · 2021-01-25T20:35:41Z

Yeah, I've nuked node modules and restarted my IDE several times to no avail. I suppose it's possible something might be conflicting with it, but I'm not sure what that would be at this point. Here are my deps:

 "dependencies": {
    "@nestjs/common": "^7.5.1",
    "@nestjs/core": "^7.5.1",
    "@nestjs/platform-express": "^7.5.1",
    "reflect-metadata": "^0.1.13",
    "rimraf": "^3.0.2",
    "rxjs": "^6.6.3"
  },
  "devDependencies": {
    "@nestjs/cli": "^7.5.1",
    "@nestjs/schematics": "^7.1.3",
    "@nestjs/testing": "^7.5.1",
    "@types/express": "^4.17.8",
    "@types/jest": "^26.0.15",
    "@types/node": "^14.14.6",
    "@types/supertest": "^2.0.10",
    "@typescript-eslint/eslint-plugin": "^4.14.1",
    "@typescript-eslint/parser": "^4.14.1",
    "eslint": "^7.18.0",
    "eslint-config-prettier": "7.1.0",
    "eslint-plugin-jsx-a11y": "^6.4.1",
    "eslint-plugin-prettier": "^3.1.4",
    "jest": "^26.6.3",
    "prettier": "^2.1.2",
    "supertest": "^6.0.0",
    "ts-jest": "^26.4.3",
    "ts-loader": "^8.0.14",
    "ts-node": "^9.1.1",
    "tsconfig-paths": "^3.9.0",
    "typescript": "^4.1.3"
  },

bradzacher · 2021-01-25T20:51:10Z

There may be multiple versions installed?
https://github.com/typescript-eslint/typescript-eslint/blob/master/docs/getting-started/linting/FAQ.md#how-do-i-check-to-see-what-versions-are-installed

Hard to say exactly - it all depends on your project setup.

timecatalyst · 2021-01-25T21:00:13Z

Looks like I'm on the right version. I'm going to try to build the project up from scratch and see where it gets me. I'll post back if I find anything. Thanks for the feedback.

% yarn list @typescript-eslint/eslint-plugin @typescript-eslint/parser
yarn list v1.22.10
warning Filtering by arguments is deprecated. Please use the pattern option instead.
├─ @typescript-eslint/eslint-plugin@4.14.1
└─ @typescript-eslint/parser@4.14.1
✨  Done in 0.33s.

timecatalyst · 2021-01-25T21:43:57Z

Okay, I rebuild the project with just typescript and linting:

package.json:
{
  "name": "eslint-test",
  "version": "0.0.1",
  "description": "",
  "author": "",
  "private": true,
  "license": "UNLICENSED",
  "scripts": {},
  "dependencies": {},
  "devDependencies": {
    "@types/node": "^14.14.22",
    "@typescript-eslint/eslint-plugin": "^4.14.1",
    "@typescript-eslint/parser": "^4.14.1",
    "eslint": "^7.18.0",
    "eslint-config-prettier": "^7.2.0",
    "eslint-plugin-prettier": "^3.3.1",
    "prettier": "^2.2.1",
    "ts-loader": "^8.0.14",
    "ts-node": "^9.1.1",
    "tsconfig-paths": "^3.9.0",
    "typescript": "^4.1.3"
  }
}

tsconfig.json:
{
  "compilerOptions": {
    "module": "commonjs",
    "declaration": true,
    "removeComments": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "allowSyntheticDefaultImports": true,
    "target": "es2017",
    "sourceMap": true,
    "outDir": "./dist",
    "baseUrl": "./",
    "incremental": true
  }
}

I have a single index.ts containing the same test code from before.

Using only the above files, I did not receive a warning on interface Foo. But, when I added in the .eslintrc.js file from the NestJS repo, the warning reappeared. I did some digging and found that removing plugin:@typescript-eslint/recommended from the extends array makes the warning disappear (along with other legitimate no-unused-vars warnings). I suspect there may be some invalid usage going on. Here's the eslintrc:

module.exports = {
  parser: '@typescript-eslint/parser',
  parserOptions: {
    project: 'tsconfig.json',
    sourceType: 'module',
  },
  plugins: ['@typescript-eslint/eslint-plugin'],
  extends: [
    'plugin:@typescript-eslint/eslint-recommended',
    'plugin:@typescript-eslint/recommended',
    'plugin:@typescript-eslint/recommended-requiring-type-checking',
    'prettier/@typescript-eslint',
    'plugin:prettier/recommended',
  ],
  root: true,
  env: {
    node: true,
    jest: true,
  },
  ignorePatterns: ['.eslintrc.js'],
  rules: {
    '@typescript-eslint/interface-name-prefix': 'off',
    '@typescript-eslint/explicit-function-return-type': 'off',
    '@typescript-eslint/explicit-module-boundary-types': 'off',
    '@typescript-eslint/no-explicit-any': 'off',
  },
};

timecatalyst · 2021-01-26T21:30:03Z

@bradzacher I think I found the culprit: "emitDecoratorMetadata": true, in tsconfig.json. If I remove that key, or set the value to false, the linter error disappears.

bradzacher · 2021-01-26T21:31:12Z

See #2972

timecatalyst added package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin triage Waiting for team members to take a look labels Jan 21, 2021

bradzacher closed this as completed Jan 21, 2021

bradzacher added duplicate This issue or pull request already exists and removed triage Waiting for team members to take a look labels Jan 21, 2021

This was referenced Jan 22, 2021

[no-use-before-define] no-use-before-define rule reports an wrong error for class method #2965

Closed

Getting no-unused-vars on constructor parameters after upgrading to the latest version of typescript and eslint #2971

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[@typescript-eslint/no-unused-vars] False positive for an interface used as a generic parameter on a function with a decorator. #2961

[@typescript-eslint/no-unused-vars] False positive for an interface used as a generic parameter on a function with a decorator. #2961

timecatalyst commented Jan 21, 2021 •

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timecatalyst commented Jan 25, 2021

timecatalyst commented Jan 26, 2021

bradzacher commented Jan 26, 2021

[@typescript-eslint/no-unused-vars] False positive for an interface used as a generic parameter on a function with a decorator. #2961

[@typescript-eslint/no-unused-vars] False positive for an interface used as a generic parameter on a function with a decorator. #2961

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timecatalyst commented Jan 21, 2021 • edited Loading

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