Summary:
This PR add ability to check that the schema is able to execute some operations. It follows the second approach outlined in the issue.

It's worth noting that the validation depends on the queryValidation parameter of the @server directive, as the query is executed against the schema (with resolvers that don't actually do anything).

Given a the sample schema jsonplaceholder.graphql and two operations posts.graphql and empty.graphql, we get the output below.

# tc check jsonplaceholder.graphql --operations posts.graphql empty.graphql

N + 1: 1

Error: Validation Error
• Unknown field "userOd" on type "Post". Did you mean "userId", "user"? [examples/operations/posts.graphql, line 5 column 5]
• Unknown field "userAd" on type "Post". Did you mean "userId", "user"? [examples/operations/posts.graphql, line 6 column 5]
•  --> 1:1
  |
1 | 
  | ^---
  |
  = expected executable_definition [examples/operations/empty.graphql, line 1 column 1]

• jsonplaceholder.graphql

schema
  @server(port: 8000, graphiql: true, hostname: "0.0.0.0", queryValidation: true)
  @upstream(baseURL: "http://jsonplaceholder.typicode.com", httpCache: true) {
  query: Query
}

type Query {
  posts: [Post] @http(path: "/posts")
}

type User {
  id: Int!
  name: String!
  username: String!
  email: String!
  phone: String
  website: String
}

type Post {
  id: Int!
  userId: Int!
  title: String!
  body: String!
  user: User @http(path: "/users/{{value.userId}}")
}

• posts.graphql

query {
  posts {
    id
    body
    userOd
    userAd
  }
}

• empty.graphql: well, it's empty

Issue Reference(s):
Fixes #416

Build & Testing:

• I ran cargo test successfully.
• I have run ./lint.sh --mode=fix to fix all linting issues raised by ./lint.sh --mode=check.

Checklist:

• I have added relevant unit & integration tests.
• I have updated the documentation accordingly (if applicable).
• I have performed a self-review of my own code.

Fun fact:

I mistakenly deleted the branch, which closed the first PR I opened.

/claim #416