Inspect non-error types to produce helpful error messages for failing resolvers (#1600)

Inspect non-error types to produce helpful error messages for failing resolvers (even though you should not throw literals, ever)

Author: kommander

src/execution/__tests__/abstract-promise-test.js

@@ -546,7 +546,7 @@ describe('Execute: Handles execution of abstract types with promises', () => {
   it('resolveType can be caught', async () => {
     const PetType = new GraphQLInterfaceType({
       name: 'Pet',
-      resolveType: () => Promise.reject('We are testing this error'),
+      resolveType: () => Promise.reject(new Error('We are testing this error')),
       fields: {
         name: { type: GraphQLString },
       },

src/execution/__tests__/executor-test.js

@@ -466,7 +466,7 @@ describe('Execute: Handles basic execution tasks', () => {
           path: ['syncError'],
         },
         {
-          message: 'Error getting syncRawError',
+          message: 'Unexpected error value: "Error getting syncRawError"',
           locations: [{ line: 5, column: 9 }],
           path: ['syncRawError'],
         },
@@ -491,12 +491,12 @@ describe('Execute: Handles basic execution tasks', () => {
           path: ['asyncReject'],
         },
         {
-          message: 'Error getting asyncRawReject',
+          message: 'Unexpected error value: "Error getting asyncRawReject"',
           locations: [{ line: 10, column: 9 }],
           path: ['asyncRawReject'],
         },
         {
-          message: '',
+          message: 'Unexpected error value: undefined',
           locations: [{ line: 11, column: 9 }],
           path: ['asyncEmptyReject'],
         },
@@ -506,7 +506,7 @@ describe('Execute: Handles basic execution tasks', () => {
           path: ['asyncError'],
         },
         {
-          message: 'Error getting asyncRawError',
+          message: 'Unexpected error value: "Error getting asyncRawError"',
           locations: [{ line: 13, column: 9 }],
           path: ['asyncRawError'],
         },

src/execution/execute.js

@@ -740,7 +740,10 @@ export function resolveFieldValueOrError<TSource>(
 // Sometimes a non-error is thrown, wrap it as an Error instance to ensure a
 // consistent Error interface.
 function asErrorInstance(error: mixed): Error {
-  return error instanceof Error ? error : new Error(error || undefined);
+  if (error instanceof Error) {
+    return error;
+  }
+  return new Error('Unexpected error value: ' + inspect(error));
 }
 
 // This is a small wrapper around completeValue which detects and logs errors