Change Request: Export `WithExit` helper type from `@eslint/core`

[jaymarvelz]

Which packages would you like to change?

• @eslint/compat
• @eslint/config-array
• @eslint/config-helpers
• @eslint/core
• @eslint/mcp
• @eslint/migrate-config
• @eslint/object-schema
• @eslint/plugin-kit

What problem do you want to solve?

All ESLint languages — JavaScript, JSON, CSS, and Markdown — require handling both entry and exit visitors for AST nodes. Currently we have to reimplement a helper type like this in each language:

type WithExit<RuleVisitorType extends RuleVisitor> = {
  [Key in keyof RuleVisitorType as
    | Key
    | `${Key & string}:exit`]: RuleVisitorType[Key];
};

What do you think is the correct solution?

It would be useful for @eslint/core to export a WithExit helper type. This should eliminate repeated boilerplate across languages.

Participation

• I am willing to submit a pull request for this change.

Additional comments

No response

[fasttime]

Makes sense to me. @eslint/plugin-kit could be also a good fit for this type, but we already have language-independent helper types such as CustomRuleDefinitionType in @eslint/core, so it makes sense to add it there. I would like an opinion from anorher team member before marking as accepted.

[lumirlumir]

I'm personally +1 on adding the WithExit type to @eslint/core for now.

Types such as CustomRuleDefinitionType and CustomRuleTypeDefinitions are imported from @eslint/core, so having only WithExit in @eslint/plugin-kit feels inconsistent.

(Maybe in the future, if there's an opportunity to move all language plugin–related types to plugin-kit, it would make sense to move them then.)

---

Also, I find the name WithExit a bit unclear—would CustomRuleVisitorWithExit or a similar name be clearer and more consistent?
Since WithExit is always used with the RuleVisitor type, I think a clearer name would be helpful here. I’d welcome other opinions on the type name.

References:

• https://github.com/eslint/css/blob/main/src/types.ts#L49-L51
• https://github.com/eslint/markdown/blob/main/src/types.ts#L132-L134
• https://github.com/eslint/json/pull/172/files#diff-c54113cf61ec99691748a3890bfbeb00e10efb3f0a76f03a0fd9ec49072e410a

[DMartens]

I agree that we should provide the helper type (the suggestion came from one of my review comments).
I think this type should be in @eslint/core as languages can define their own phases and do not have to have an exit phase or may want to specify the phase in the selector in a different way.
Or an alternative would be to create a new package only for shared types for the different provided languages.