5/n - Add erroring on seeing relayFieldErrors

Reviewed By: tyao1

Differential Revision: D51944692

fbshipit-source-id: ef0afb0cecbf87228ec2aec283a9754d52b028d1

packages/relay-runtime/util/handlePotentialSnapshotErrors.js

@@ -18,6 +18,7 @@ import type {
   RelayResolverErrors,
 } from '../store/RelayStoreTypes';
 
+import {RelayFieldError} from '../store/RelayErrorTrie';
 import RelayFeatureFlags from './RelayFeatureFlags';
 
 function handlePotentialSnapshotErrors(
@@ -34,7 +35,10 @@ function handlePotentialSnapshotErrors(
       error: resolverError.error,
     });
   }
-  if (RelayFeatureFlags.ENABLE_FIELD_ERROR_HANDLING) {
+  if (
+    RelayFeatureFlags.ENABLE_FIELD_ERROR_HANDLING &&
+    errorResponseFields != null
+  ) {
     if (errorResponseFields != null) {
       for (const fieldError of errorResponseFields) {
         const {path, owner, error} = fieldError;
@@ -47,6 +51,13 @@ function handlePotentialSnapshotErrors(
         });
       }
     }
+
+    if (RelayFeatureFlags.ENABLE_FIELD_ERROR_HANDLING_THROW_BY_DEFAULT) {
+      throw new RelayFieldError(
+        `Relay: Unexpected response payload - this object includes an errors property in which you can access the underlying errors`,
+        errorResponseFields.map(({path, owner, error}) => error),
+      );
+    }
   }
 
   if (missingRequiredFields != null) {