no-underscore-dangle to check function params

[hnipps]

What rule do you want to change?
no-underscore-dangle

Does this change cause the rule to produce more or fewer warnings?
More warnings

How will the change be implemented? (New option, new default behavior, etc.)?
The updated rule will check if param Identifiers of FunctionDeclarations and ArrowFunctionExpressions have dangling underscores.

I suggest that underscore dangle in these situations is disallowed by default and can be configured using the same pattern as "allowAfterThis" and "allowAfterSuper".

Please provide some example code that this change will affect:

const test = (_arg) => { };
function myfunc(_arg) { };

What does the rule currently do for this code?
No error thrown.

What will the rule do after it's changed?
Throw an error because the function params have dangling underscores.

Are you willing to submit a pull request to implement this change?
Yes

[hnipps]

This update will help users migrating from TSLint to ESLint to reach feature parity because the TSLint variable-name rule already has the proposed feature.

[webOS101]

I would suggest this be configurable, as well, or, perhaps allow a single underscore in parameter names by default, given the common pattern of using _ for unused parameter.

[kaicataldo]

I agree that this seems like an oversight of the rule and support this change. I do think it needs to be put behind an option to avoid a breaking change (maybe allowFunctionParams: true by default) and that in addition to FunctionDeclarations and ArrowFunctionExpressions, I think it should also check FunctionExpressions.

[hnipps]

Is this still being evaluated? Or do we have a decision?

[kaicataldo]

I'll champion this. We still need support from two other team members before we can mark this as accepted.

[ron23]

I would love to see that as well. We're migrating from TSLint and would really like to keep the consistency. Thanks!

[anikethsaha]

Marking this as accepted as there are 3 +1 from team members.

I think allowFunctionParams might be a good approach and name which will be true by default as mentioned above