`fixable` property only necessary when `meta` is present

What did you expect to happen?

Per the docs:

Important: Without the fixable property, ESLint does not apply fixes even if the rule implements fix functions. Omit the fixable property if the rule is not fixable.

Based on this, I would expect a rule without any meta at all to also not be fixable.

What actually happened? Please include the actual, raw output from ESLint.

A rule without meta is successfully fixed when it has a fixer.

The docs are true, however, if there is a meta object of some sort (including an empty object); in such a case, an error will be reported that fixable is necessary if the rule attempts to add a fixer. But if there is no meta object at all, fixable is not necessary for fixes to be applied for the rule.

I am not expecting breaking changes to start preventing fixers without meta; I’d just expect the docs to mention that rules still without the recommended meta property at all are currently still fixable.

[nzakas]

Because we don’t guarantee fixes to be applied, I think we can fix this behavior to work as it was originally intended. The result of using a rule with a legacy fixer is that it will only warn and not fix, which I wouldn’t consider a breaking change.

The bigger question is why RuleTester isn’t testing for this already. That’s one of our primary ways of enforcing rule standards and I’m surprised there’s not a check in there.

Here’s what I would suggest as a path forward:

1. Make an announcement about this explaining that it is a bug and we know it will affect people.
2. Update RuleTester to check that meta.fixable is present whenever a fix is provided. Release this first without changing how rules actually work.
3. Fix the bug with how rule fixes are being applied in a subsequent release.

[mdjermanovic]

As clarified in today’s TSC meeting, steps 1-3 will apply to legacy (function) format as well.

Meaning that, as of v8.0.0, only rules that export meta.fixable (which implies that it’s a new-format rule, and that it exports meta) can be fixable. In v8.0.0, an error will be thrown during linting whenever a rule that doesn’t satisfy this condition produces a fix.