TSLint does not respect the underscore pattern for unused parameters

[pronebird]

Bug Report

• TSLint version: 5.12.1
• TypeScript version: 3.x
• Running TSLint via: CLI

Actual behavior

TSLint does not respect the underscore pattern for unused parameters.

p.s: The code below is stripped down a little to demonstrate the issue.

Take 1

Use unused parameters:

ipcRenderer.on(event, (unusedEvent: Electron.Event, newState: T) => fn(newState));

Get punched by TypeScript:

error TS6133: 'unusedEvent' is declared but its value is never read.

Take 2

Underscore the unused parameter

ipcRenderer.on(event, (_unusedEvent: Electron.Event, newState: T) => fn(newState));

Get praised by TypeScript:

$ tsc
✨ Done in 8.15s.

Take 3

Try linting the code that TypeScript is happy about:

ERROR: 297:28 variable-name variable name must be in lowerCamelCase, PascalCase or UPPER_CASE

Very cool.

with tslint.json configuration:

{
  "defaultSeverity": "error",
  "extends": [
    "tslint:latest",
    "tslint-config-prettier"
  ],
  "rules": {
    "max-classes-per-file": false,
    "object-literal-sort-keys": false
  }
}

Expected behaviour

TSLint should respect the underscore pattern for unused parameters.

[JoshuaKGoldberg]

Hi @pronebird! Have you tried using the allow-leading-underscore option? https://palantir.github.io/tslint/rules/variable-name/

[pronebird]

Hi @JoshuaKGoldberg!

Yep and it works, but I would like this pattern to be only allowed for unused parameters only. I think it makes sense because it's more of an exception. Normally we use camelCase.

[JoshuaKGoldberg]

Gotcha (and agreed). This is a duplicate of #3442, then. +1 for allowing this!

[pronebird]

Ah right, thanks! 👍