I found some issues with directive definitions:
- I couldn't use `on FIELD_DEFINITION`, I believe because `FIELD` was parsed
first in `executableDirectiveLocation`. I've combined both
`executableDirectiveLocation` and `typetypeSystemDirectiveLocation` into one
function which can reorder them to ensure every directive location gets a fair
chance at parsing.
Not actually to do with directives, some literals weren't being parsed
correctly.
- The GraphQL spec defines list to be `[]` or `[Value]`, but empty literal lists
weren't being parsed correctly because of using `some` instead of `many`.
- The GraphQL spec defines objects to be `{}` or `{Name: Value}`, but empty
literal objects had the same issue.
ca0f0bd32d