feat: additional rule metadata for deprecations

designs/2024-deprecated-rule-metadata/README.md

@@ -0,0 +1,281 @@
+- Repo: eslint/eslint
+- Start Date: 2024-02-20
+- RFC PR: <https://github.com/eslint/rfcs/pull/124>
+- Authors: [bmish](https://github.com/bmish), [DMartens](https://github.com/DMartens)
+
+# Support additional metadata for rule deprecations
+
+## Summary
+
+<!-- One-paragraph explanation of the feature. -->
+
+This RFC suggests a format for storing additional information in rule metadata about rule deprecations and replacement rules, allowing tooling (e.g. documentation generators) to generate more informative deprecation notices.
+
+## Motivation
+
+<!-- Why are we doing this? What use cases does it support? What is the expected
+outcome? -->
+
+There are long-time [rule meta properties](https://eslint.org/docs/latest/extend/custom-rules#rule-structure) `meta.deprecated` and `meta.replacedBy` that have been intended to document when rules are deprecated and what their replacement rule(s) are. For the most part, usage would look something like this:
+
+```js
+module.exports = { meta: { deprecated: true, replacedBy: ['replacement-rule-name'] } };
+```
+
+These properties are often used for generating plugin/rule documentation websites and in documentation tooling like [eslint-doc-generator](https://github.com/bmish/eslint-doc-generator).
+
+But there are some limitations to this current format:
+
+- Simply providing the replacement rule name as a string doesn't yield much context/explanation of the replacement/deprecation. That means documentation tooling / websites and code editors can only generate limited information to present about the situation.
+- Some rules provide the replacement rule name with the plugin prefix as in `prefix/rule-name` while others just provide it as `rule-name`, which can result in ambiguity about whether the replacement rule is in the same plugin, a different third-party plugin, or ESLint core. And for third-party plugins, there's no easy way to automatically determine where their documentation is located or how to link to them.
+
+## Detailed Design
+
+<!--
+   This is the bulk of the RFC.
+
+   Explain the design with enough detail that someone familiar with ESLint
+   can implement it by reading this document. Please get into specifics
+   of your approach, corner cases, and examples of how the change will be
+   used. Be sure to define any new terms in this section.
+-->
+
+We propose to extend `meta.deprecated` rule property schemas to reduce ambiguity and allow additional key details to be represented, described below using TypeScript types for clarity:
+
+```ts
+type RuleMeta = {
+  deprecated?:
+    | boolean // Existing boolean option, backwards compatible.
+    | string // Shorthand property for general deprecation message, such as why the deprecation occurred. Empty strings are forbidden as they are falsy.
+    | DeprecatedInfo // Proposed extension
+
+  /** @deprecated */
+  replacedBy?: string[] // Deprecate the top-level property and "move" into the "deprecated" object
+};
+
+/* At least one property is required */
+type DeprecateInfo = {
+  info?: Message
+  replacedBy?: (string|ReplacedByInfo)[] // An empty array explicitly states that there is no replacement
+}
+
+/* At least one property is required */
+type ReplacedByInfo = {
+  plugin?: string | Specifier // name should be "eslint" if the replacemenet is an ESLint core rule. Omit the property if the replacement is in the same plugin
+  rule?: string | Specifier
+  info?: string | Message
+  kind?: ReplacementKind // Defaults to "moved" if missing
+  deprecatedSince?: Version // Helps users gauge when to migrate and useful for documentation
+  availableUntil?: Version | null // The estimated version when the rule is removed (probably the next major version). null means the rule is "frozen" (will be available but will not be changed)
+}
+
+type Message = {
+  message: string // General message presented to the user. Content depends on the property (e.g. for the key rule why the rule is deprecated or for info how to replace the rule)
+  url:            // URL to more information about this deprecation in general.
+}
+
+type Specifier = {
+  name: string // Name of the rule / configuration / ...
+  url: string // URL to more information about this deprecation in general.
+}
+
+type ReplacementKind =
+  'moved' |  // The rule has moved to another plugin if plugin is set, otherwise the rule is renamed in the same plugin
+  'merged' | // The rule merged with another rule
+  'option'   // The current rule behavior is available as an option in the replacement rule
+
+/* Version string of the package containing the rule */
+type Version = string
+```
+
+The `meta.replacedBy` property is moved into the `meta.deprecated` property as `meta.replacedBy` requires `meta.deprecated` to be set.
+The reason for this is that a rule logically must be marked as deprecated to be replaced by another rule which it currently can be.
+
+### Example
+Real-world example of how this could be used based on the situation in <https://github.com/eslint/eslint/issues/18053>:
+
+```js
+// lib/rules/semi.js
+module.exports = {
+  meta: {
+    deprecated: {
+      message: 'Stylistic rules are being moved out of ESLint core.',
+      url: 'https://eslint.org/blog/2023/10/deprecating-formatting-rules/',
+      replacedBy: [
+        {
+          plugin: {
+          name: '@stylistic/js',
+          url: 'https://eslint.style/',
+        },
+        rule: 'https://eslint.style/rules/js/semi',
+        },
+      ],
+    },
+  },
+};
+```
+
+
+This data could be used by documentation websites and tooling like [eslint-doc-generator](https://github.com/bmish/eslint-doc-generator) to generate notices and links like:
+
+> semi (deprecated) \
+> Replaced by [semi](https://eslint.style/rules/js/semi) from [@stylistic/js](https://eslint.style/). \
+> Use the `foo` option on the new rule to achieve the same behavior as before. [Read more](https://example.com/how-to-migrate-to-the-new-semi-rule). \
+> Stylistic rules are being moved out of ESLint core. [Read more](https://eslint.org/blog/2023/10/deprecating-formatting-rules/).
+
+We can also support the same `meta.deprecated` and `meta.replacedBy` properties on configurations and processors (the other kinds of objects exported by ESLint plugins), replacing `rule` with `config` or `processor` as needed. This would be part of the effort to standardize documentation properties in <https://github.com/eslint/eslint/issues/17842>.
+
+### Shorthand
+The shorthand for the properties `plugin`, `rule` and `info` is just a string representing either the `name`/`message` or the `url` based on its content.
+If it starts with a protocol (e.g. `https://`) the property should be interpreted as if only the `url` property is set, otherwise it should be interpreted as `name`/`message` property.
+This shorthand also applies for the existing `meta.deprecated` which then applies for the `meta.deprecated.info` properties.
+Some examples:
+```js
+{ meta: { deprecated: { plugin: 'https://eslint.style' } } }   // <=> { meta: { deprecated: { plugin: { url: 'https://eslint.style' } } } }
+{ meta: { deprecated: { plugin: '@eslint-stylistic/js' } } }   // <=> { meta: { deprecated: { plugin: { name: '@eslint-stylistic/js' } } } }
+{ meta: { deprecated: 'https://eslint.style/guide/migration' } // <=> { meta: { deprecated: { info: { url: 'https://eslint.style/guide/migration' } } } }
+```
+
+### Changes
+In terms of actual changes inside ESLint needed for this:
+
+- Mention the new schema in the [custom rule documentation](https://eslint.org/docs/latest/extend/custom-rules#rule-structure)
+- Ensure these properties are allowed on configurations, parsers and processors
+- Add any additional information to these properties in core rules as desired (such as in <https://github.com/eslint/eslint/issues/18053>)
+- Update ESLint's website generator to take into account the additional information for rule doc deprecation notices
+- Update [LintResult.usedDeprecatedRules](https://github.com/eslint/eslint/blob/0f5df509a4bc00cff2c62b90fab184bdf0231322/lib/eslint/eslint.js#L197-L211)
+
+External changes:
+
+- Update the [types](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/b77d83e019025017b06953907cb77f35e4231714/types/eslint/index.d.ts#L734) in @types/eslint
+- Update the [types](https://github.com/typescript-eslint/typescript-eslint/blob/82cb9dd580f62644ed988fd2bf27f519177a60bd/packages/utils/src/ts-eslint/Rule.ts#L70) in @typescript-eslint/eslint
+- Update eslint-doc-generator to handle the new information: <https://github.com/bmish/eslint-doc-generator/issues/512>
+- Update the metadata for the most common plugins
+- Consider implementing an [eslint-plugin-eslint-plugin](https://github.com/eslint-community/eslint-plugin-eslint-plugin) rule to encourage more complete deprecation information to be stored in these properties
+
+## Documentation
+
+<!--
+    How will this RFC be documented? Does it need a formal announcement
+    on the ESLint blog to explain the motivation?
+-->
+
+We don't necessarily need a formal announcement for this. The aforementioned changes to the rule documentation page and types should be sufficient.
+
+However, this update could be covered in a blog post about general rule documentation best practices, if anyone ever has an interest in writing something like that.
+
+## Drawbacks
+
+<!--
+    Why should we *not* do this? Consider why adding this into ESLint
+    might not benefit the project or the community. Attempt to think
+    about any opposing viewpoints that reviewers might bring up.
+
+    Any change has potential downsides, including increased maintenance
+    burden, incompatibility with other tools, breaking existing user
+    experience, etc. Try to identify as many potential problems with
+    implementing this RFC as possible.
+-->
+
+There are some limited [backwards compatibility](#backwards-compatibility-analysis) concerns for third-party tooling.
+
+## Backwards Compatibility Analysis
+
+<!--
+    How does this change affect existing ESLint users? Will any behavior
+    change for them? If so, how are you going to minimize the disruption
+    to existing users?
+-->
+
+Existing rules will continue to be backwards-compatible with the new format.
+
+Changing the format of these properties mainly affects third-party documentation tooling and websites that use this information, and not ESLint users nor ESLint plugins directly.
+
+For the most part, the new `meta.deprecated` format should be backwards-compatible, as code is often written to check simply for a truthy value inside of `meta.deprecated`, e.g. `if (rule.meta.deprecated) { /* ... */ }`, which will continue to work as expected. The code needs to be updated if:
+- it checks specifically for the boolean `true` value in `meta.deprecated`
+- it checks for whether the rule is deprecated by checking for a non-empty `meta.replacedBy`
+- retrieves rule names from `meta.replacedBy`
+
+Overall, a limited number of third-party tools that might be affected, and these should be trivial to fix when impacts are discovered.
+
+We do not need to consider this to be a breaking change in terms of [ESLint's semantic versioning policy](https://github.com/eslint/eslint#semantic-versioning-policy).
+
+## Alternatives
+
+<!--
+    What other designs did you consider? Why did you decide against those?
+
+    This section should also include prior art, such as whether similar
+    projects have already implemented a similar feature.
+-->
+
+### Do nothing
+
+This would leave the current `meta.deprecated` and `meta.replacedBy` properties as they are, which would continue to be ambiguous and limited in the information they can provide.
+
+### Create a new property
+
+Create a new property, e.g. `meta.deprecation`,
+
+## Open Questions
+
+<!--
+    This section is optional, but is suggested for a first draft.
+
+    What parts of this proposal are you unclear about? What do you
+    need to know before you can finalize this RFC?
+
+    List the questions that you'd like reviewers to focus on. When
+    you've received the answers and updated the design to reflect them,
+    you can remove this section.
+-->
+
+1. Is there additional deprecation information we'd like to represent? Note that additional information can always be added later, but it's good to consider any possible needs now.
+2. Should `meta.deprecated.plugin.id` accommodate different package registries (e.g. [jsr](https://jsr.io/) with `jsr:eslint-plugin-example`)
+3. Should the exact regular expression for the shorthand which decides whether it is a description or URL be specified?
+4. Should the shorthand also be applied for the string form of the `meta.deprecated` property?
+5. Which "extension points" (rules, processors, configurations, parsers, formatters) shold be supported?
+6. Should the `rule` key be dependent on the "extension point" (e.g. `processor` for processors) or renamed (e.g. ``) so that it is the same property name for all?
+
+## Help Needed
+
+<!--
+    This section is optional.
+
+    Are you able to implement this RFC on your own? If not, what kind
+    of help would you need from the team?
+-->
+
+I should be able to handle the minimal changes needed in ESLint core, and can kick off some of the changes needed in community projects.
+
+## Frequently Asked Questions
+
+- Why not provide a property to describe how to migrate to the replacement rule which requires an option to be set?
+  - The options of the replacement rule could change and it is unlikely that a deprecated rules gets updated to accommodate the change
+
+<!--
+    This section is optional but suggested.
+
+    Try to anticipate points of clarification that might be needed by
+    the people reviewing this RFC. Include those questions and answers
+    in this section.
+-->
+
+## Related Discussions
+
+<!--
+    This section is optional but suggested.
+
+    If there is an issue, pull request, or other URL that provides useful
+    context for this proposal, please include those links here.
+-->
+
+- [The original RFC](https://github.com/eslint/rfcs/pull/116)
+- [The issue triggering this RFC](https://github.com/eslint/eslint/issues/18061)
+- Inspirations
+  - <https://github.com/jsx-eslint/eslint-plugin-react/pull/3469#discussion_r1002316631>
+  - <https://github.com/eslint/eslint/issues/5774#issuecomment-220640368>
+- Related
+  - <https://github.com/eslint/eslint/issues/17842>
+  - <https://github.com/eslint/eslint/issues/18694>
+  - <https://github.com/eslint/eslint/issues/18053>