Summary

ShallowTypeRefCollector (introduced with FastBuilder in #4196) performs
shallow scans of types and directives to collect GraphQLTypeReference objects
for later replacement. In three places it called scanArgumentType(arg) on a
GraphQLArgument but never called scanAppliedDirectives(arg.getAppliedDirectives()).
It also had no handling to descend into GraphQLEnumValueDefinition objects to
scan their applied directives.

The result: when FastBuilder is used with programmatically-constructed types
carrying GraphQLTypeReference objects in applied directive argument types on
field arguments, enum values, or directive definition arguments, those references
are never resolved. The AppliedDirectiveArgumentsAreValid validator then sees a
GraphQLTypeReference where it expects a real input type and throws:

InvalidSchemaException: Invalid argument 'x' for applied directive of name 'y'

(This does not manifest when types are built via FastSchemaGenerator + SDL,
because SchemaGeneratorHelper.buildInputType resolves types at construction
time. It manifests when FastBuilder is used directly with programmatically-built
types.)

Changes

Three locations in ShallowTypeRefCollector fixed:

• handleObjectType / handleInterfaceType — added
  scanAppliedDirectives(arg.getAppliedDirectives()) inside the field-argument
  loop of both methods, alongside the existing scanArgumentType(arg) call.

• handleTypeDef — added handleEnumType() which iterates over
  GraphQLEnumValueDefinition values and scans their applied directives. (Applied
  directives on the enum type itself were already covered by the existing
  GraphQLDirectiveContainer branch.)

• handleDirective — added scanAppliedDirectives(argument.getAppliedDirectives())
  inside the directive-argument loop alongside the existing scanArgumentType call.

Adds four regression tests in FastBuilderTest covering all three fix locations:
applied directive on object type field argument, interface field argument, enum
value, and directive definition argument.

Related

Bug in the FastBuilder / ShallowTypeRefCollector introduced in #4196.