feat: support additional metadata for rule deprecations

[bmish]

Summary

This RFC suggests a format for storing additional information in rule metadata about rule deprecations and replacement rules, allowing automated documentation and website tooling to generate more informative deprecation notices.

Related Issues

• Change Request: Support additional rule metadata for deprecations eslint#18061

[ljharb]

This looks great!

[ljharb]

should an empty string be prohibited here, so that “not deprecated” is unambiguously false always?

[ljharb]

one of these properties should be required - so like { message } | { url } | { message, url }

[ljharb]

same here

[JoshuaKGoldberg]

LGTM, with the strong caveat that I've never reviewed an RFC as a member of the committer team before and thus should not be taken very seriously. 😄

Very excited about this one though! I think it'll be great for docs generation & helping folks migrate to new rules. 🚀

[JoshuaKGoldberg]

[Clarification] Are both "eslint-plugin-example" and "example" allowed?

[bmish]

By "shorthand property", I just mean that a string can be provided instead of the more detailed object format.

My intention was for the full plugin name to be provided here eslint-plugin-foo or @foo/eslint-plugin or whatever so there wouldn't be any ambiguity. Simply providing the plugin prefix foo doesn't necessarily tell us the full plugin name as there can be various formats...

[JoshuaKGoldberg]

[Praise] This is a really good demonstration of the proposed change and its benefits. (and also why eslint-doc-generator is great!)

[fasttime]

A typical ESLint deprecation notice includes the version of ESLint that introduced the deprecation, for example "ESLint v8.53.0" for the semi rule:

This rule was deprecated in ESLint v8.53.0. Please use the corresponding rule in @stylistic/eslint-plugin-js.

I think we want to keep that information, so we would need to store a deprecatedSince version key in meta.replacedBy.info or meta.replacedBy.note, depending on the name we choose, and then use it to generate the notice, if we want to automate that process.

[JoshuaKGoldberg]

[Question] Are there existing examples in the wild of rules that have stayed deprecated for a long time? I'm wondering if there really would be much pain from, say:

1. Adding meta.deprecated.replacedBy and marking meta.replacedBy as a @deprecated alias in ESLint v9
2. Removing meta.replacedBy in ESLint v10

The rest of the rule metadata I'd be much more hesitant to change. But this Sourcegraph search for replacedBy in lint/rule files shows only a little under 300 code results, with the occasional script.

[ljharb]

Given that i almost never do major bumps, all of the import, react, and jsx-a11y plugins have examples - but many are unlikely to be using replacedBy, since i only learned about it within the last year.

[bmish]

It sounds like @JoshuaKGoldberg has a preference for consolidating the properties, whereas @ljharb is neutral or slightly opposed? I'm open to hearing more opinions and still open to changing the proposal on this based on reviewer feedback.

It is true that a migration from meta.replacedBy to meta.deprecated.replacedBy would be a relatively lightweight and inconsequential migration, compared to more painful ESLint migrations or breaking changes we have performed in the past.

I fleshed out this section with some more pros and cons.

Interested to hear more feedback on this decision.

[ljharb]

I mean in general I prefer to avoid breaking changes - in particular because then, how will an eslint plugin support both eslint 9 and 10, given that RuleTester fails with unknown properties?

[JoshuaKGoldberg]

support both eslint 9 and 10

Another strategy could be to leave it @deprecated for two major versions instead of one. Just to give plguins more time to adopt. I'm personally not in favor of this as major versions don't drop very frequently.

given that RuleTester fails with unknown properties

You could write some quick code around the RuleTester usage that adds/deletes properties as needed. Given how rarely it is for plugins to support quite so long a list of backwards compatibility versions as yours, I imagine the total amount of community work there isn't very high.

I think this point also emphasizes how not-very-breaking this is compared to potential other schema changes. RuleTester failing with unknown properties only impacts the plugin being tested, right? So even if a few plugins such as eslint-plugin-import need to do a bit of hackery in tests, I think that'd be justified for the user benefit of a more understandable+unified property.

[bmish]

@nzakas @mdjermanovic I'm interested to hear if either of you have a preference between keeping the two existing properties or consolidating meta.replacedBy into meta.deprecated.replacedBy?

[mdjermanovic]

I'd prefer consolidating meta.replacedBy into meta.deprecated.replacedBy.

[nzakas]

👍 consolidating.

[JoshuaKGoldberg]

[Content] From eslint/eslint#18061 (comment):

The only other point that comes to mind for me is being able to specify options in the new rule. https://github.com/typescript-eslint/tslint-to-eslint-config -> https://github.com/typescript-eslint/tslint-to-eslint-config/blob/470d44de20beb7c7366de993edb8898d0766b8aa/docs/Architecture/Linters.md might be a good reference. Deprecated rules could map to multiple new ones, including specifying options and changed or missing functionality.

The "specifying options and changed or missing functionality" point might be relevant. How common is it that a rule deprecation points to a new rule with a particular option?

The only example that comes to mind for me is https://typescript-eslint.io/rules/no-type-alias. It's replaced by two rules:

• Behavior change, but recommended: https://typescript-eslint.io/rules/consistent-type-definitions with the default "interface" option
• Preserving the original behavior: https://eslint.org/docs/latest/rules/no-restricted-syntax, with an option like ["TypeAliasDeclaration"]

I personally don't think there's a need for to add functionality to the RFC for options (yet?). There are a lot of edge cases to account for and the message string is probably more than sufficient for most of them. But I think it'd be good to mention it as out of scope.

Another alternative that could be mentioned is storing a conversion function, the way tslint-to-eslint-config does. That in theory could be useful for users who want to get exact conversions... but again, I think is unnecessary work and best to just leave as out of scope.

[bmish]

These are great callouts. I added a note about these. I do agree we can probably skip these for now in favor of just using message, but open to adding them now or later if someone wants to champion them.

[nzakas]

I'd prefer to explicitly not encourage discussion of replacements options as part of a rule's meta data. These are subject to change, and keeping that information in sync with a rule in a different repo is a maintenance headache. The source of truth should be in the replacement rule's docs -- the only job of the deprecated rule meta information is to successfully get users from the deprecated rule to the new rule's docs. Whether and which options to use should be found there.

[bmish]

This is an open design question. If we stick with two separate properties, what does it mean for meta.deprecated to be false or omitted but meta.replacedBy to contain a value? It seems implied that a rule that has replacements would be deprecated, but it might not be explicitly marked as so which is concerning.

[nzakas]

Perhaps this is an opportunity for a RuleTester check?

[JoshuaKGoldberg]

Thinking from the perspective of types: this is tough to represent precisely in TypeScript. Either...

• ... the types are straightforward ({ deprecated?: boolean; replacedBy?: ReplaceBy }) and allow not-good situations ({ replacedBy: [...] })
• ... the types are something more complex such as a union of objects, and are more difficult to understand

Complex types are generally a symptom of complex code ideas. Which I think is true here. It's not intuitive to answer these questions.

Not saying that TypeScript specifically is a reason to do anything 😄 - just that its type system is a good way to sniff out conceptual complexity.

[nzakas]

Overall this LGTM. Just left a few notes on various things, but overall I think this is a well-thought-out proposal that could be implemented without disruption.

[nzakas]

I think meta.replacedBy[].meta is a bit confusing. It seems like the purpose of this meta is really to provide additional info about the replacement. Perhaps note or info would be a more appropriate name?

[mdjermanovic]

info sounds good to me.

[nzakas]

Perhaps this is an opportunity for a RuleTester check?

[nzakas]

I'd prefer to explicitly not encourage discussion of replacements options as part of a rule's meta data. These are subject to change, and keeping that information in sync with a rule in a different repo is a maintenance headache. The source of truth should be in the replacement rule's docs -- the only job of the deprecated rule meta information is to successfully get users from the deprecated rule to the new rule's docs. Whether and which options to use should be found there.

[mdjermanovic]

Would we keep the same type of the usedDeprecatedRules property on LintResult objects that are returned from ESLint APIs and passed to formatters?

Currently, it's:

usedDeprecatedRules ({ ruleId: string; replacedBy: string[] }[])

If we keep the same type, then we'd need to update the code that generates this property. If we change the type so that replacedBy is returned as-is (array of strings or an object) from rule meta, then it could be considered as a breaking change.

[aladdin-add]

@bmish there are a few more comments here. :)

[mdjermanovic]

@bmish just to check, are you still working on this?

[nzakas]

@bmish Just checking in. Are you still working on this?

[nzakas]

@bmish there are some outstanding comments to address. Are you still interested in finishing this RFC?

[bmish]

I'd like to finish it up but it might be a while until I find some time.

[nzakas]

@bmish can you give us a rough timeframe so we can know when to follow up?

[nzakas]

@bmish it's been a month since the last ping. Do you have a timeframe for when you plan on finishing this up?

[nzakas]

Hi everyone - we're looking for someone who's interested in this RFC to pick it up and push it over the finish line. If you're interested, please leave a comment here.

[DMartens]

I'm interested in finishing this.
I'm in favor of only using the deprecated key as there is a strict relationship between deprecated and replacedBy and
checking whether the legacy form is used is simple: if (rule.meta.deprecated || "replacedBy" in rule.meta).
With that and the notes from others it would like this:

type RuleMeta = {
	deprecated?: {
		replacedBy?: ...
		plugin?: string | { name?: string, url?: string } // Question: Should it be required that the name is its id on npm? or allow other registries such as jsr. Also worth documenting is if it should be set if it is from the same plugin
		rule?: string | { name?: string, url?: string }
		info?: string | { message?: string, url?: string } // Originally "meta"

		// Additions
		deprecatedSince?: string // Version string since when the rule is deprecated
		availableUntil?: null | string // Version or date when the rule will be removed or null if the rule is frozen
	}
}

Another thing worth mentioning is we could get rid of requiring one property (either url or name) in the object forms if the shorthand string should be interpreted smartly: if it starts with a protocol (e.g. https:// it is shorthand for the url and otherwise for message or name. Then the object forms would require both properties to be set.

[nzakas]

@DMartens I'd say put all of those thoughts into the RFC and we can go from there.

[fasttime]

@DMartens Thanks for picking up the work on this RFC. Feel free to open a new pull request as you probably don't have write access to the source repo here.

[nzakas]

@DMartens are you still interested in picking this up?

[DMartens]

Sorry, I wanted to proofread it the next day and forgot. Anyways the proposal is continued in #124.

[nzakas]

No worries. We'll close this and continue the discussion on #124.