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.

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.