chore: move callback and object typedefs to a new types.d.ts

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🛠 Repo: Split type declarations into standalone .d.ts files #5347
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Creates a new lib/types.d.ts and moves every @callback and @typedef {Object} to it. A new tsconfig.json & tsc script can be run to verify that the types in that file can be type checked.

Does not yet validate types in .js files (#4154, #4228). You can preview those by switching tsconfig.json's allowJs to checkJs. I made sure there are no more "Cannot find name ..." errors but fixing the rest of the ~650+ will be a lot more work. Much of the code will be much easier to get type-safe when it's ported from manual function prototypes to classes (#5025). I also held off porting all the info from @types/mocha there to keep the changes minimal.

Does not yet try to pull in types or descriptions from @types/mocha. That would be a bigger change too.

Moves error constants from errors.js to error-constants.js to avoid circular dependency errors.

[voxpelli]

Why everything in one large .d.ts?

Also: You can try to use (still sometimes buggy) the @import to import instead of using typedef, eg:

/** @import { Foo } from './bar.js' */

[JoshuaKGoldberg]

Why everything in one large .d.ts?

I don't have preferences on where to organize types, since this feels like a transient "we'll clean things up over time anyway" kind of situation to me 😄. Do you have a preference for where things should go?

[JoshuaKGoldberg]

ping @voxpelli did you mean for #5351 (comment) to be a full review? I'm not clear on whether you're requesting changes and waiting on me, or just posting thoughts pending a full review?

[voxpelli]

@JoshuaKGoldberg Posting thoughts pending a full review, thanks for pinging and asking 🙏

[mark-wiemer]

Pretty good, requested a few changes :)

[Copilot]

Pull Request Overview

This PR centralizes JSDoc type definitions into a new lib/types.d.ts, moves error constants to lib/error-constants.js, and updates module files to import those typedefs. It also adds a tsconfig.json and GitHub Actions job to run tsc for type checking.

• Consolidated all @callback/@typedef declarations into types.d.ts
• Extracted error constants into lib/error-constants.js and updated imports
• Added a tsc script and workflow step for validating the new types

Reviewed Changes

Copilot reviewed 47 out of 47 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lib/reporters/base.js	Removed inline FullErrorStack typedef and added import from types.d.ts
lib/plugin-loader.js	Removed inline PluginDefinition and PluginLoaderOptions typedefs, added imports
lib/nodejs/worker.js	Removed inline BufferedEvent/MochaOptions typedefs, added imports and updated @param
lib/nodejs/serializer.js	Removed inline SerializedEvent/SerializedWorkerResult typedefs, added imports
lib/nodejs/reporters/parallel-buffered.js	Removed inline BufferedEvent typedef and added import
lib/nodejs/parallel-buffered-runner.js	Removed inline SigIntListener/FileRunner typedefs, added imports
lib/nodejs/buffered-worker-pool.js	Removed inline typedefs, added imports for WorkerPoolOptions, MochaOptions, results
lib/mocha.js	Removed many inline typedefs, added imports for DoneCB, fixtures, options, reporter types
lib/interfaces/tdd.js	Added Suite typedef import
lib/interfaces/qunit.js	Added Suite typedef import
lib/interfaces/common.js	Added Context and Mocha typedef imports
lib/interfaces/bdd.js	Added Suite typedef import
lib/errors.js	Removed inline constants, imported from error-constants.js, no longer exports constants
lib/error-constants.js	New file exporting all Mocha error constants
lib/context.js	Added Runnable typedef import
lib/cli/watch-run.js	Added typedef imports for FSWatcher, Mocha, BeforeWatchRun, FileCollectionOptions, etc.
lib/cli/run-option-metadata.js	Updated JSDoc {{string:string[]}} to Record<string,string[]>
lib/cli/run-helpers.js	Added imports for Mocha, MochaOptions, UnmatchedFile, Runner
lib/cli/collect-files.js	Switched error import to error-constants, added FileCollectionOptions/Response imports
.github/workflows/mocha.yml	Added tsc job to run the TypeScript compiler for validation

Comments suppressed due to low confidence (2)

lib/errors.js:418

• The constants object was removed from this module’s exports but is still documented under module:lib/errors. If backward compatibility is required, re-export constants here or update documentation to reflect the new location.

module.exports = {

lib/error-constants.js:4

• The @memberof module:lib/errors tag is misleading in this standalone file. Consider changing it to module:lib/error-constants or removing the @memberof directive.

* @memberof module:lib/errors

[mark-wiemer]

@JoshuaKGoldberg I'm good to merge this if you are