Split schema parsing

[dackroyd]

Allow the schema definition parsing to be applied independently of making it executable.

This enables multiple executable schemas to be created from a single schema parse. This also gives access to the AST without attaching the resolver immediately.

The change in type for SchemaOpt isn't strictly a 100% backward compatible change. It should however be non-breaking for typical cases. Breakages may exist if usages define their own equivalent type from func(*graphql.Schema).

[pavelnikolov]

Allow the schema definition parsing to be applied independently of making it executable.

This also gives access to the AST without attaching the resolver immediately.

This is already available if you pass nil for the resolver, isn't it? It's documented in the ParseSchema comment.

[dackroyd]

This is already available if you pass nil for the resolver, isn't it? It's documented in the ParseSchema comment.

It's possible to parse a schema without a resolver, yes. That result cannot then be attached to a resolver later on, without re-parsing the schema from scratch, however.

By splitting the phases, it becomes possible to parse the schema and access the AST without immediately attaching a resolver, and being able to use the already parsed schema to create any number of executable schemas. These may use identical resolvers and schema options, or use different ones.

An example case might be to apply strict depth and query length limits on a publicly exposed schema, whilst allowing larger limits to the same schema when exposed internally and/or behind authentication.