suggestion: option for variable-name rule to allow leading underscore only for unused params

[sethbrenith]

I'm just promoting a comment by @mohsen1 in this discussion into its own issue for visibility.

Can variable-name know about unused params? Most of us don't want to allow leading underscore elsewhere.

const _varName = 1; 
//    ~~~~~~~~       <-- this still needs to be a lint error
function foo(_: string, __: number, bar: boolean) {
  console.log('only interested in', bar);
}

[ajafff]

The latest version of the naming-convention rule in my package tslint-consistent-codestyle allows you to configure exactly what you want:
https://github.com/ajafff/tslint-consistent-codestyle/blob/master/docs/naming-convention.md#examples
The important part for you is

"naming-convention": [
  true,
  // forbid leading and trailing underscores and enforce camelCase on EVERY name. will be overridden by subtypes if needed
  {"type": "default", "format": "camelCase", "leadingUnderscore": "forbid", "trailingUnderscore": "forbid"},
  ...
  // allow leading underscores for unused parameters, because `tsc --noUnusedParameters` will not flag underscore prefixed parameters
  // all other rules (trailingUnderscore: forbid, format: camelCase) still apply
  {"type": "parameter", "modifiers": "unused", "leadingUnderscore": "allow"}
]

[sethbrenith]

Excellent, that's just what we were looking for! Thanks!

[adidahiya]

Thanks for the link @ajafff. I would like this functionality incorporated into the variable-name rule if possible, as an isolated enhancement separate from other features of the naming-convention rule.

[mgol]

This is now more important as in TypeScript 2.9 no-unused-variable is deprecated and if you switch to the compiler noUnusedLocals & noUnusedParameters options, leading underscores are a hint to the compiler that those params should be allowed to be unused. I'm making such changes to my code base but now the variable-name rule complains...

EDIT: Hmm, actually, it's already supported, see https://palantir.github.io/tslint/rules/variable-name/. Should this issue be closed?

[sethbrenith]

@mgol All I see at that link is "allow-leading-underscore". This suggestion was about allowing leading underscores only for unused variables (and still banning them elsewhere).

[mgol]

@sethbrenith Ah, sorry, I misinterpreted your request.

[aryzing]

@ajafff Since you're most familiar, Would you mind giving this PR a go?

@JoshuaKGoldberg given your participation in #3558, not sure if you're actively looking into this?

[JoshuaKGoldberg]

@aryzing no plans on my part to address this issue, but if you want to send a PR that'd be great! 😊

[pronebird]

Oh man it would be great to fix this. @ts-ignore-ing this is so messed up.

[JoshuaKGoldberg]

☠️ TSLint's time has come! ☠️

TSLint is no longer accepting most feature requests per #4534. See typescript-eslint.io for the new, shiny way to lint your TypeScript code with ESLint. ✨

It was a pleasure open sourcing with you all!

[JoshuaKGoldberg]

🤖 Beep boop! 👉 TSLint is deprecated 👈 (#4534) and you should switch to typescript-eslint! 🤖

🔒 This issue is being locked to prevent further unnecessary discussions. Thank you! 👋