Add option to extend gatsby-config.js

[TidyIQ]

Summary

Add the ability to extend an existing gatsby-config.js. Any additional options added will overwrite the extended config options. Basically, the same implementation as "extends" in tsconfig.json.

Basic example

// gatsby-config.js

module.exports = {
  extends: "path/to/different/gatsby-config.js",
  ...overwrites
}

Motivation

I am creating an npm package that is essentially a template for Gatsby projects. Since it involves many plugins, gatsby-config.js needs to be modified for each project that uses the package. Currently the only options are to:

1. Force users to copy-paste the gatsby-config.js contents themselves
2. Clone from a repo

These are poor options as any time the npm package is updated and requires a change in gatsby-config.js (e.g. new plugins are added, settings are changed, plugins removed, etc.), the user has to manually apply the changes themselves to their own gatsby-config.js file.

With this proposed change, users would simply need to run npm update [package_name] and they would immediately receive the new up-to-date configuration file.

This works extremely well for packages such as Typescript and ESLint and it would be fantastic to have this feature in Gatsby.

[lannonbr]

Would Gatsby Themes possibly help with this? You can put a base config in the theme and then when you use a theme, the site's gatsby-config is merged with any gatsby-configs from other themes. As well, as you upgrade a theme, the gatsby-config in the theme updates with it so a consumer of the theme doesn't need to touch it.

Here's the docs for Themes: https://www.gatsbyjs.org/docs/themes/what-are-gatsby-themes

[TidyIQ]

Oh nice, that sounds perfect. I didn't know that was a thing. I'll look into it more, thanks!

[lannonbr]

Alright. I'm going to close this for now as this seems to be resolved

[AryanJ-NYC]

@lannonbr Any idea what I'm doing wrong here? I'm hoping to extend @narative/gatsby-theme-novela's use of gatsby-transformer-remark: https://github.com/AryanJ-NYC/webdev-coach-blog/blob/move-to-narrative/gatsby-config.js#L32.

The links still do not open as expected.

[lannonbr]

Let me open a new issue about this