[RFC][LSP] Pluggable schema loading

Hi all,

Here at FB we have some schema extensions that live in a separate file and are applied during the build. While this is not particularly relevant for GraphiQL, we really want to have this as part of the LSP. Therefore I propose the following:

• In the configuration of the LSP (.graphqlrc), the user can specify the following:
  • (required) a package that provides two functions: async init() and async getSchema(). The latter returns the latest GraphQLSchema. Hopefully this can work in a similar way to babel plugins or webpack loaders.
  • (optional) arguments that are provided to the init function, before the getSchema function is called for the first time.
  • (optional) a glob relative to the .graphqlrc that triggers the schema to be reloaded on file change.

With this, I believe we can provide a very flexible schema loading experience. The first schema loaders we implement should probably be: a file schema loader to provide the current LSP experience and an introspection query schema loader to make it work with GraphiQL.

[acao]

The interface that the typescript language service uses for adding LSP plugins is interesting, and is designed to work in browsers, vscode, monaco, etc https://github.com/microsoft/TypeScript/wiki/Writing-a-Language-Service-Plugin

We could do something similar with -interface, or possibly a layer on top of it designed for greater parity with existing vscode-<language>-languageservice implementations

[acao]

Also, I wouldn’t rule out alternative schema loading patterns, even alternative protocols being more readily supported for graphiql-1.0.0-alpha if that matters. for example, using wss to locally (or over the wire?) transmit json-rpc from a language server. so hopefully we can be a good reference implementation of these possibilities