TypeScript type mismatch with Joi (and testing plugins)

[webstackdev]

Since TS support for gatsby-* files landed in 4.9, I've been refactoring my core Gatsby files to take advantage of it. I've run into a problem involving types for the pluginOptionsSchema gatsby-node API method.

I think at one point the TS types for Joi (validation library) were out of sync as that project moved out of the @Hapi namespace. The gatsby-plugin-utils has a modified set of types and re-exports the Joi object, along with a testPluginOptionsSchema function.

I have some functionality that I implemented in a Joi extension so that it was easier to use template-d error messages. I need the Joi types for CustomHelpers, Extension, andExtensionFactory which aren't exported from the hard-code version of Joi types in gatsby-plugin-utils (which removes the Joi namespace from the typings). The type is available on Joi e.g. Joi.ExtensionFactory from the joi package, but the two sets of typings (Joi's and gatsby-plugin-utils) have gotten out of sync. The Joi interface for ValidationError has an _original: any key, where the gatsby-plugin-utils version has an _object: any key instead so I get type errors.

My interim solution is a local copy of gatsby-plugin-utils with modified typings. I think the right solution is to modify the Gatsby typings:

import { Joi } from 'joi'
export interface PluginOptionsSchemaArgs {
  Joi: Joi.Root
}

Another possibility is to move packages/gatsby-plugin-util/src/joi.ts to either packages/gatsby/src/bootstrap/load-plugins/ or packages/gatsby/src/joi-schemas/ in an appropriate file, and modify the type of the exported Joi object to Joi.Root. That way there's a central place to manage typings and extensions to the Joi object used in plugin options validation.

I'd be happy to push a PR through but opened a discussion because I'm not sure the best route to go. There was some work on plugin option validation to use dot env vars in gatsby-config, but it doesn't seem like that work went anywhere and might be reasonably stripped out (note from @mxstbr October 2021 that the functionality was being considered). So I don't think the reason for providing a custom Gatsby-specific type for the Joi object used in plugin option schema validation may still even be relevant.

On a tenuously related note:

I plan to create a plugin with a few additional Joi validation testing methods in it. I'm not sure if it'll be useful to a wider audience, but it had me thinking about Gatsby testing plugins generally. I'll end up with a name like gatsby-plugin-testing-joi in a vendor namespace. There's lots of variations on the second slug segment for Gatsby plugins now; a testing one is a suggestion I'd add (e.g. gatsby-testing-joi). A Jest plugin seems like it could provide drop-in Jest config with all of the piddly files built in and reasonable defaults.

[moonmeister]

Hey @webstackdev, Some history:

In this commit I un-copied the custom types cause I didn't think we needed them. Max redid it in a later commit. If I remember correctly it was something to do with Joi's typing for external async validations which we explicitly wanted to support. Ah, I found it, here's the discussion where we revert the change and the reason why.

I'm not sure the status of the dotenv() stuff you mentioned, but if we can find a way to not copy all the Joi types out to modify one thing then a PR would be great!