chore(gatsby-source-contentful): move to pluginOptionsSchema

[mxstbr]

Based on the pluginOptionsSchema support added in #27242 this adds a pluginOptionsSchema to gatsby-source-contentful based on the already-existing Joi schema and custom option validation this plugin has.

[pvdz]

I assume this is because there's an early return, but since this isn't a .ts file, I'm not sure?

[abhiaiyer91]

For external fro Joi API doc https://github.com/sideway/joi/blob/master/API.md#anyexternalmethod-description

which can either return a replacement value, undefined to indicate no change, or throw an error.

[abhiaiyer91]

This looks good to me! whats the deal with test suite errors tho?

[mxstbr]

I haven't deleted any of the existing tests for the previous custom validation step yet. 😬

[mxstbr]

I cleaned up the error message to make it clearer, this should be ready to ship as a first MVP! 👍

[mfrachet]

Now that we can rely on https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-plugin-utils/src/test-plugin-options-schema.ts maybe it can be a good idea to write tests and provide examples of the way to use it in a concrete case?

[abhiaiyer91]

Do we need to wrap exports with the experimental flag?

[mxstbr]

maybe it can be a good idea to write tests and provide examples of the way to use it in a concrete case?

Yes for sure! 👍

Do we need to wrap exports with the experimental flag?

Yes we should unfortunately because the "does Node API exist" check throws an error in the current version of gatsby. See #27370.

[wardpeet]

Nice work! Looks good to me!