Add `commentPattern` option to `no-fallthrough` rule

What version of ESLint are you using? 2.5.3 What rule do you want to change? no-fallthrough What code should be flagged as incorrect with this change?

/*eslint no-fallback: ["error", { "commentPattern": "break[\\s\\w]*omitted" }]*/
switch(foo) {
    case 0: a();
    /* fallthrough */
    default: c();
}

What happens when the rule is applied to this code now? Errors: Expected a 'break' statement before 'case'. Expected a 'break' statement before 'default'.

It seems useful to be able to customize the comment pattern for intentional fallthrough (default pattern for now is /falls?\s?through/i), especially when one tends to write comments in a language other than english. Consider:

/*eslint no-fallback: ["error", { "commentPattern": "break" }]*/
switch (foo) {
    case 0: a();
    // break пропущен умышленно!
    case 1: b();
}

[ilyavolodin]

I guess it makes sense for no-empty and no-empty-function to accept any comment vs. no-fallthrough. I would be OK with adding a new option to both no-fallthrough and no-default-case to accept RegEx.

[nzakas]

Okay, we will use this issue to track no-fallthrough. Please open a separate issue for no-default-case.