case-style-ternaries: format nested ternaries in case style

[arthur-fontaine]

Clear and concise description of the problem

I find that nested ternaries are very difficult to read, even with the multiline-ternary rule enabled.

Example:

const animalName =
  pet.canBark() ?
    pet.isScary() ?
      'wolf'
    : 'dog'
  : pet.canMeow() ? 'cat'
  : 'probably a bunny';

Suggested solution

In their article, Prettier suggests to format the code above would be formatted as follows:

const animalName =
  pet.isScary() ? 'wolf'
  : pet.canBark() ? 'dog'
  : pet.canMeow() ? 'cat'
  : 'probably a bunny';

I find it more clear and readable.

This feature could be implemented with a new rule.

I think this is a stylistic issue in some point of view, but I am not sure this is a stylistic issue in the point of view of eslint-stylistic, so this issue is maybe out of concern...

Alternative

flatTernaryExpressions: true, option on indent can result to something similar, but does not refacto the logic. In fact, flatTernaryExpressions: true should be used with this rule to get the wanted result.

Validations

• Follow our Code of Conduct
• Read the Contributing Guide.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

Contributes

• If this feature request is accepted, I am willing to submit a PR to fix this issue

[kecrily]

I prefer to add it when it becomes Prettier's default behavior, just in case it doesn't end up being adopted. Of course if you want to add it, that's fine with me.