Use error ctor for syntax errors rather than mutation

Fixes issue where syntax errors were reported with poor messages.

src/error/GraphQLError.js

@@ -10,58 +10,64 @@
 
 import { getLocation } from '../language';
 import type { Node } from '../language/ast';
+import type { Source } from '../language/source';
 
 
 export class GraphQLError extends Error {
   message: string;
   stack: string;
   nodes: ?Array<Node>;
-  source: any;
-  positions: any;
+  source: Source;
+  positions: Array<number>;
   locations: any;
 
   constructor(
     message: string,
     // A flow bug keeps us from declaring nodes as an array of Node
     nodes?: Array<any/* Node */>,
-    stack?: ?string
+    stack?: ?string,
+    source?: Source,
+    positions?: Array<number>
   ) {
     super(message);
     this.message = message;
+
     Object.defineProperty(this, 'stack', { value: stack || message });
     Object.defineProperty(this, 'nodes', { value: nodes });
-  }
-}
 
-// Note: flow does not yet know about Object.defineProperty with `get`.
-Object.defineProperty(GraphQLError.prototype, 'source', ({
-  get() {
-    var nodes = this.nodes;
-    if (nodes && nodes.length > 0) {
-      var node = nodes[0];
-      return node && node.loc && node.loc.source;
-    }
-  }
-}: any));
+    // Note: flow does not yet know about Object.defineProperty with `get`.
+    Object.defineProperty(this, 'source', ({
+      get() {
+        if (source) {
+          return source;
+        }
+        if (nodes && nodes.length > 0) {
+          var node = nodes[0];
+          return node && node.loc && node.loc.source;
+        }
+      }
+    }: any));
 
-Object.defineProperty(GraphQLError.prototype, 'positions', ({
-  get() {
-    var nodes = this.nodes;
-    if (nodes) {
-      var positions = nodes.map(node => node.loc && node.loc.start);
-      if (positions.some(p => p)) {
-        return positions;
+    Object.defineProperty(this, 'positions', ({
+      get() {
+        if (positions) {
+          return positions;
+        }
+        if (nodes) {
+          var nodePositions = nodes.map(node => node.loc && node.loc.start);
+          if (nodePositions.some(p => p)) {
+            return nodePositions;
+          }
+        }
       }
-    }
-  }
-}: any));
+    }: any));
 
-Object.defineProperty(GraphQLError.prototype, 'locations', ({
-  get() {
-    var positions = this.positions;
-    var source = this.source;
-    if (positions && source) {
-      return positions.map(pos => getLocation(source, pos));
-    }
+    Object.defineProperty(this, 'locations', ({
+      get() {
+        if (this.positions && this.source) {
+          return this.positions.map(pos => getLocation(this.source, pos));
+        }
+      }
+    }: any));
   }
-}: any));
+}

src/error/syntaxError.js

@@ -24,12 +24,12 @@ export function syntaxError(
   var location = getLocation(source, position);
   var error = new GraphQLError(
     `Syntax Error ${source.name} (${location.line}:${location.column}) ` +
-    description + '\n\n' + highlightSourceAtLocation(source, location)
+    description + '\n\n' + highlightSourceAtLocation(source, location),
+    undefined,
+    undefined,
+    source,
+    [ position ]
   );
-  error.nodes = null;
-  error.positions = [ position ];
-  error.locations = [ location ];
-  error.source = source;
   return error;
 }
 

src/language/__tests__/parser.js

@@ -47,6 +47,27 @@ describe('Parser', () => {
 
   it('parse provides useful errors', () => {
 
+    var caughtError;
+    try {
+      parse('{');
+    } catch (error) {
+      caughtError = error;
+    }
+
+    expect(caughtError.message).to.equal(
+      `Syntax Error GraphQL (1:2) Expected Name, found EOF
+
+1: {
+    ^
+`
+    );
+
+    expect(caughtError.positions).to.deep.equal([ 1 ]);
+
+    expect(caughtError.locations).to.deep.equal([
+      { line: 1, column: 2 }
+    ]);
+
     expect(
       () => parse(
 `{ ...MissingOn }