introspection implements the spec defined in https://github.com/facebook/graphql/blob/master/spec/Section%204%20--%20Introspection.md#schema-introspection.

AddError is a convenience method for adding an error to the current response.

AddErrorf is a convenience method for adding an error to the current response.

ChainFieldMiddleware add chain by FieldMiddleware.

CollectAllFields returns a slice of all GraphQL field names that were selected for the current resolver context.

CollectFields returns the set of fields from an ast.SelectionSet where all collected fields satisfy at least one of the GraphQL types passed through satisfies.

This is just a convenient wrapper method for CollectFields.

Errors are intentionally serialized first based on the advice in https://github.com/facebook/graphql/commit/7b40390d48680b15cb93e02d46ac5eb249689876#diff-757cea6edf0288677a9eea4cfc801d87R107 and https://github.com/facebook/graphql/pull/384.