[@typescript-eslint/no-unused-vars] does not work?

[AnderssonPeter]

• 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": {
     "no-unused-vars": "off",
     "@typescript-eslint/no-unused-vars": ["warn", { "vars": "all", "args": "all" }],
  }
}

@Injectable()
export class BackendCommunicationService {
    private keepRotating = false; <-- unused

    constructor(
        private logger: Logger, <-- unused
        private database: Database, <-- unused
        private http: HttpClient
    ) {}

tsconfig

{
  "compileOnSave": false,
  "compilerOptions": {
    "baseUrl": "./",
    "outDir": "./dist/out-tsc",
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "noImplicitOverride": true,
    "noPropertyAccessFromIndexSignature": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true,
    "sourceMap": true,
    "declaration": false,
    "downlevelIteration": true,
    "experimentalDecorators": true,
    "moduleResolution": "node",
    "importHelpers": true,
    "target": "es2021",
    "module": "es2020",
    "lib": [
      "es2021",
      "dom"
    ]
  },
  "angularCompilerOptions": {
    "enableI18nLegacyMessageIdFormat": false,
    "strictInjectionParameters": true,
    "strictInputAccessModifiers": true,
    "strictTemplates": true
  }
}

Expected Result

It should warn me about the unused fields/properties.

Actual Result

No warning is given

Additional Info

I'm using Angular 13, How do i generate a debug lint? (Normally I just run ng lint but it doesn't seem to have a debug flag

Versions

package	version
@typescript-eslint/eslint-plugin	5.13.0
@typescript-eslint/parser	5.13.0
TypeScript	4.5.5
ESLint	8.10.0
node	14.17.6

[JoshuaKGoldberg]

no-unused-vars is specifically for variables, not class properties. https://typescript-eslint.io/rules/no-unused-vars -> https://eslint.org/docs/rules/no-unused-vars

I think it'd be reasonable to add in a rule like no-unused-class-members that suggests removing private ones. Note that it'd have to be a suggestion rather than a fix (https://eslint.org/docs/developer-guide/working-with-rules): #4571 (comment).

#private members are completely safe to mark as unused because they are 100%, runtime enforced to be only accessible within the class they are defined.

However private members are not. They are accessible outside the class via instance['member'] (yes, that's valid and safe TS). And are ultimately just type-only sugar for a normal class member.

Which means we cannot statically detect the valid usages across module boundaries.

This is generally I would recommend using #private instead of private in all modern code.

In the meantime TypeScript's built-in noUnusedLocals setting can catch unused class members.

cc @bradzacher since I know you've worked around this area a bunch in the past.

[bradzacher]

Yeah we definitely could implement a private class member rule as suggested in #4571. It's probably a good idea so that we can further help people migrate off of the TS flag.

Though this definitely shouldn't be implemented within no-unused-vars - as you mention it's for variables, and properties aren't variables.

So I'll close this and tag #4571 as accepting PRs.

[ChristianHardy]

Greetings, I have an error using no-unused-vars @bradzacher can you give me a hand with this?

[JoshuaKGoldberg]

@ChristianHardy please don't post on closed, unrelated issues. That spams the thread and is not very discoverable for other folks who have your issue.

For info on the @typescript-eslint/no-unused-vars rule (hint: and how to configure it), please see https://typescript-eslint.io/rules/no-unused-vars.