Add executeExchange for using an executable schema

[andyrichardson]

About

Exchange for executing queries locally using an executable schema.

This may be particularly useful for us when making example projects as we could mock responses here rather than implementing a server.

[kitten]

I think @mxstbr is already maintaining a package for that. We may just want to send a PR to update it a little https://github.com/mxstbr/urql-exchange-schema

[mxstbr]

Happy to merge that into core!

[andyrichardson]

Let me know what you want to do 👍

[changeset-bot]

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[kitten]

@JoviDeCroock @andyrichardson assuming we'll want to get this merged soon, but we'll only need some minor documentation for this after a rebase, and let's stick it into a new exchanges/execute package?

[andyrichardson]

@kitten Yeah I'm happy to sort that out but you're going to have to explain the monorepo to me.

The exchange is 61 lines, no new dependencies, and will be tree shaken if not in use. Do we want this exchange to be a standalone package in /exchanges?

Also, where do the docs for standalone packages go?

[kitten]

I think bundling an exchange would only make sense if a majority of users use it? Although, I can totally see an exchange being "moved" into core, when it crosses that threshold. For now, I'd play it safe. It looks like when execute is bundled (be that because it's bundled accidentally, or tree-shaking fails, or not an option, etc) it adds a lot of heft: apollographql/apollo-link#968

I've got some docs in the CONTRIBUTING.md guide that should help 👍 but happy to also pair on that or sth 👍 https://github.com/FormidableLabs/urql/blob/master/CONTRIBUTING.md#how-do-i-add-a-new-package

[andyrichardson]

@kitten thanks for the explanation - I've moved it to /exchanges

[leebenson]

FWIW, this exchange fixed an issue I was experiencing with https://github.com/mxstbr/urql-exchange-schema, in that queries via SSR were being executed once for each exchange.

So a typical set-up of:

exchanges: [
  dedupExchange,
  cacheExchange,
  ssr,
  schemaExchange(schema, { context }),
]

... would actually run the query four times.

This is a subtle bug that's easy to overlook, since the first query that's run is the one that winds up being rendered back to the client.

Just a heads-up @mxstbr in case it made sense to update your own package while waiting for this to merge.

[kitten]

To get this up-to-date we just need to make sure that the config files match (package.json fields, some are linted by the prepare script), tsconfig.json changes, creating an empty CHANGELOG, etc

[amyboyd]

To get this up-to-date we just need to make sure that the config files match (package.json fields, some are linted by the prepare script), tsconfig.json changes, creating an empty CHANGELOG, etc

The branch has been rebased on master and these files are matching the other extensions.

A few other misc changes -- see commit log.