Errors thrown from resolvers have the execution path

This path is also passed in the `info` object to resolvers.
This information is useful for ease of debugging and more detailed logging.

Author: Slava

src/__tests__/starWarsIntrospection-test.js

@@ -205,6 +205,13 @@ describe('Star Wars Introspection Tests', () => {
                 kind: 'LIST'
               }
             },
+            {
+              name: 'secretBackstory',
+              type: {
+                name: 'String',
+                kind: 'SCALAR'
+              }
+            },
             {
               name: 'primaryFunction',
               type: {
@@ -284,6 +291,14 @@ describe('Star Wars Introspection Tests', () => {
                 }
               }
             },
+            {
+              name: 'secretBackstory',
+              type: {
+                name: 'String',
+                kind: 'SCALAR',
+                ofType: null
+              }
+            },
             {
               name: 'primaryFunction',
               type: {

src/__tests__/starWarsQuery-test.js

@@ -364,4 +364,80 @@ describe('Star Wars Query Tests', () => {
       expect(result).to.deep.equal({ data: expected });
     });
   });
+
+  describe('Reporting errors raised in resolvers', () => {
+    it('Correctly reports error on accessing secretBackstory', async () => {
+      const query = `
+        query HeroNameQuery {
+          hero {
+            name
+            secretBackstory
+          }
+        }
+      `;
+      const expected = {
+        hero: {
+          name: 'R2-D2',
+          secretBackstory: null
+        }
+      };
+      const expectedErrors = [ 'secretBackstory is secret.' ];
+      const result = await graphql(StarWarsSchema, query);
+      expect(result.data).to.deep.equal(expected);
+      expect(result.errors.map(e => e.message)).to.deep.equal(expectedErrors);
+      expect(
+        result.errors.map(e => e.originalError.executionPath)).to.deep.equal(
+          [ [ 'hero', 'secretBackstory' ] ]);
+    });
+
+    it('Correctly reports error on accessing secretBackstory in a list', async () => {
+      const query = `
+        query HeroNameQuery {
+          hero {
+            name
+            friends {
+              name
+              secretBackstory
+            }
+          }
+        }
+      `;
+      const expected = {
+        hero: {
+          name: 'R2-D2',
+          friends: [
+            {
+              name: 'Luke Skywalker',
+              secretBackstory: null,
+            },
+            {
+              name: 'Han Solo',
+              secretBackstory: null,
+            },
+            {
+              name: 'Leia Organa',
+              secretBackstory: null,
+            },
+          ]
+        }
+      };
+      const expectedErrors = [
+        'secretBackstory is secret.',
+        'secretBackstory is secret.',
+        'secretBackstory is secret.',
+      ];
+      const result = await graphql(StarWarsSchema, query);
+      expect(result.data).to.deep.equal(expected);
+      expect(result.errors.map(e => e.message)).to.deep.equal(expectedErrors);
+      expect(
+        result.errors.map(e => e.originalError.executionPath)
+      ).to.deep.equal(
+        [
+          [ 'hero', 'friends', 0, 'secretBackstory' ],
+          [ 'hero', 'friends', 1, 'secretBackstory' ],
+          [ 'hero', 'friends', 2, 'secretBackstory' ],
+        ]);
+    });
+
+  });
 });

src/__tests__/starWarsSchema.js

@@ -102,6 +102,7 @@ const episodeEnum = new GraphQLEnumType({
  *     name: String
  *     friends: [Character]
  *     appearsIn: [Episode]
+ *     secretBackstory: String
  *   }
  */
 const characterInterface = new GraphQLInterfaceType({
@@ -125,6 +126,10 @@ const characterInterface = new GraphQLInterfaceType({
       type: new GraphQLList(episodeEnum),
       description: 'Which movies they appear in.',
     },
+    secretBackstory: {
+      type: GraphQLString,
+      description: 'All secrets about their past.',
+    },
   }),
   resolveType: character => {
     return getHuman(character.id) ? humanType : droidType;
@@ -140,6 +145,7 @@ const characterInterface = new GraphQLInterfaceType({
  *     name: String
  *     friends: [Character]
  *     appearsIn: [Episode]
+ *     secretBackstory: String
  *   }
  */
 const humanType = new GraphQLObjectType({
@@ -168,6 +174,13 @@ const humanType = new GraphQLObjectType({
       type: GraphQLString,
       description: 'The home planet of the human, or null if unknown.',
     },
+    secretBackstory: {
+      type: GraphQLString,
+      description: 'Where are they from and how they came to be who they are.',
+      resolve: () => {
+        throw new Error('secretBackstory is secret.');
+      },
+    },
   }),
   interfaces: [ characterInterface ]
 });
@@ -181,6 +194,7 @@ const humanType = new GraphQLObjectType({
  *     name: String
  *     friends: [Character]
  *     appearsIn: [Episode]
+ *     secretBackstory: String
  *     primaryFunction: String
  *   }
  */
@@ -206,6 +220,13 @@ const droidType = new GraphQLObjectType({
       type: new GraphQLList(episodeEnum),
       description: 'Which movies they appear in.',
     },
+    secretBackstory: {
+      type: GraphQLString,
+      description: 'Construction date and the name of the designer.',
+      resolve: () => {
+        throw new Error('secretBackstory is secret.');
+      },
+    },
     primaryFunction: {
       type: GraphQLString,
       description: 'The primary function of the droid.',

src/error/PathedError.js

@@ -0,0 +1,28 @@
+/* @flow */
+/**
+ *  Copyright (c) 2015, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+
+export class PathedError extends Error {
+  message: string;
+  stack: string;
+  executionPath: Array<string | number>;
+
+  constructor(
+    message: string,
+    stack?: ?string,
+    executionPath: Array<string | number>
+  ) {
+    super(message);
+    this.message = message;
+    this.executionPath = executionPath;
+
+    Object.defineProperty(this, 'stack', { value: stack || message });
+  }
+}

src/error/index.js

@@ -9,6 +9,7 @@
  */
 
 export { GraphQLError } from './GraphQLError';
+export { PathedError } from './PathedError';
 export { syntaxError } from './syntaxError';
 export { locatedError } from './locatedError';
 export { formatError } from './formatError';

src/error/locatedError.js

@@ -9,6 +9,7 @@
  */
 
 import { GraphQLError } from './GraphQLError';
+import { PathedError } from './PathedError';
 
 
 /**
@@ -17,7 +18,7 @@ import { GraphQLError } from './GraphQLError';
  * document responsible for the original Error.
  */
 export function locatedError(
-  originalError: ?Error,
+  originalError: ?PathedError,
   nodes: Array<any>
 ): GraphQLError {
   const message = originalError ?