[RFC] Add explicit context arg to graphql execution

[leebyron]

This BREAKING change introduces a new argument to the GraphQL execution API which is presented to resolution functions: context.

This solves a long-standing point of confusion about the correct way to represent authentication or a "viewer context" in which a query is executed.

Previously, we suggested that the rootValue contain any authentication tokens, however this led to awkward code:

resolve: (val, args, { rootValue: { authToken } }) { ... }

Which can now be written as:

resolve: (val, args, authToken) { ... }

The info object is still created and provided to resolution functions, and the rootValue is still provided within it, however it is now the fourth argument rather than the third.

[coveralls]

Coverage increased (+0.0004%) to 99.385% when pulling 188f8be on context into 43992e3 on master.

[freiksenet]

You probably meant

resolve: (val, args, { authToken }) { ... }

Right?

[freiksenet]

I like the change otherwise, it clears the slightly confusing "root value as context" pattern. Also destructuring in resolve became much easier.

[JeffRMoore]

I think its a good idea, not for the de-structuring sugar, but to give each value a single responsiblity.

[coveralls]

Coverage increased (+0.0003%) to 99.421% when pulling d7cc6f9 on context into 576b6a1 on master.

[joewood]

Stupid question: - why wasn't the argument added after the AST info rather than before to avoid the breaking change?

[leebyron]

The breaking change is undesirable, but the final state of the API is much better. The now-fourth info argument will only very rarely be accessed, and that also allows us some opportunities for future performance tuning.

[leggsimon]

Apologies if this a stupid question, pretty new to graphQL and am updating our versions. Just to clarify,
This

...
    technology: {
      type: Page,
      resolve: (root, _, { rootValue: { flags, backend = backendReal }}) =>
        backend(flags).capi.page(sources.technology.uuid)
    },
...

Now becomes

...
    technology: {
      type: Page,
      resolve: (root, _, { flags, backend = backendReal }) =>
        backend(flags).capi.page(sources.technology.uuid)
    },
...

Is that right?