Fix Panic on Introspection of Schema using ToJSON

[dackroyd]

Introspection via ToJSON works differently when used via the Schema.ToJSON function than when making an introspection query from a client such as GraphiQL. In the later case, introspection uses the Schema's registered resolver, while in the former case, a resolvable.Schema is faked

Without the Meta being set on this resolvable.Schema (following the recent changes to address race conditions around the Meta schema), this resulted in a panic when using this form of schema introspection.

[dackroyd]

Fixes #327

[bmhatfield]

I was able to confirm that this PR resolves my issue by adding this fork as a remote and checking out this branch:

[bhatfield graphql-go]% git remote add dackroyd https://github.com/dackroyd/graphql-go.git
[bhatfield graphql-go]% git fetch dackroyd
remote: Enumerating objects: 9, done.
remote: Counting objects: 100% (9/9), done.
remote: Compressing objects: 100% (6/6), done.
remote: Total 9 (delta 3), reused 9 (delta 3), pack-reused 0
Unpacking objects: 100% (9/9), done.
From github.com:dackroyd/graphql-go
 * [new branch]      bug/fix-data-race-on-schema-parsing   -> dackroyd/bug/fix-data-race-on-schema-parsing
 * [new branch]      bug/fix-panic-on-introspection-tojson -> dackroyd/bug/fix-panic-on-introspection-tojson
 * [new branch]      experimental-lexer                    -> dackroyd/experimental-lexer
 * [new branch]      master                                -> dackroyd/master
 * [new branch]      new-resolvers                         -> dackroyd/new-resolvers
[bhatfield graphql-go]% git checkout dackroyd/bug/fix-panic-on-introspection-tojson
Note: checking out 'dackroyd/bug/fix-panic-on-introspection-tojson'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b <new-branch-name>

HEAD is now at e571531 Fix Panic on Introspection of Schema using ToJSON

[bmhatfield]

Out of curiosity, is there any particular reason why this hasn't been merged yet?

[dackroyd]

I assume that @pavelnikolov has not yet had time to revisit this since I made the corrections for schemas without resolvers

[pavelnikolov]

Thanks, Dave! It looks awesome! 🎉