Draft: Schema validation Wip

This Wip MR aims to prove out schema validation according to spec

It is designed to be rewritten, ideally with a strategy that makes as few passes over the document as possible.

Will fix rubocops after rewriting it.

• 5.1 Documents
  • 5.1.1 Executable definitions
• 5.2 Operations
  • 5.2.1 Named operation defs
  • 5.2.2 Anonymous operation defs
  • 5.2.3 Subscription operation defs
• 5.3 Fields
  • 5.3.1 Field selections
  • 5.3.2 Field selection merging
  • 5.3.3 Leaf field selections
• 5.4 Arguments
  • 5.4.1 Argument names
  • 5.4.2 Argument uniqueness
    • 5.4.2.1 Required Args
• 5.5 Fragments
  • 5.5.1 Fragment Declarations
    • 5.5.1.1 Fragment name uniqueness
    • 5.5.1.2 Fragment spread type existence
    • 5.5.1.3 Fragments on composite types
    • 5.5.1.4 Fragments must be used
  • 5.5.2 Fragment spreads
    • 5.5.2.1 Fragment spread target defined
    • 5.5.2.2 Fragment spreads must not form cycles
    • 5.5.2.3 Fragment spread is possible
      • 5.5.2.3.1 Object spreads in object scope
      • 5.5.2.3.2 Abstract spreads in object scope
      • 5.5.2.3.3 Object spreads in abstract scope
      • 5.5.2.3.4 Abstract spreads in abstract scope
• 5.6 Values
  • 5.6.1 values of correct type
  • 5.6.2 Input object field names
  • 5.6.3 Input object field uniqueness
  • 5.6.4 Input object required fields
• 5.7 Directives
  • 5.7.1 Directives are defined
  • 5.7.2 Directives are in valid locations
  • 5.7.3 Directives are unique per location
• 5.8 Variables
  • 5.8.1 Variable uniqueness
  • 5.8.2 Variables are input types
  • 5.8.3 All variable uses defined
  • 5.8.4 All variables used
  • 5.8.5 All variable usages are allowed.