Do not enforce query @directive locations.

Since SchemaDirectiveVisitor cannot visit query types, we should not throw
an exception if a SchemaDirectiveVisitor fails to implement a visitor
method for a query type location.

Fixes #680.

src/schemaVisitor.ts

@@ -62,6 +62,11 @@ export abstract class SchemaVisitor {
       return false;
     }
 
+    if (this === SchemaVisitor) {
+      // The SchemaVisitor class implements every visitor method.
+      return true;
+    }
+
     const stub = SchemaVisitor.prototype[methodName];
     if (method === stub) {
       // If this.prototype[methodName] was just inherited from SchemaVisitor,
@@ -642,7 +647,8 @@ export class SchemaDirectiveVisitor extends SchemaVisitor {
 
       each(decl.locations, loc => {
         const visitorMethodName = directiveLocationToVisitorMethodName(loc);
-        if (! visitorClass.implementsVisitorMethod(visitorMethodName)) {
+        if (SchemaVisitor.implementsVisitorMethod(visitorMethodName) &&
+            ! visitorClass.implementsVisitorMethod(visitorMethodName)) {
           // While visitor subclasses may implement extra visitor methods,
           // it's definitely a mistake if the GraphQLDirective declares itself
           // applicable to certain schema locations, and the visitor subclass

src/test/testDirectives.ts

@@ -1233,4 +1233,30 @@ describe('@directives', () => {
       Human
     );
   });
+
+  it('does not enforce query directive locations (issue #680)', () => {
+    const visited = new Set<GraphQLObjectType>();
+    const schema = makeExecutableSchema({
+      typeDefs: `
+      directive @hasScope(scope: [String]) on QUERY | FIELD
+
+      type Query @hasScope {
+        oyez: String
+      }`,
+
+      schemaDirectives: {
+        hasScope: class extends SchemaDirectiveVisitor {
+          public visitObject(object: GraphQLObjectType) {
+            assert.strictEqual(object.name, 'Query');
+            visited.add(object);
+          }
+        }
+      }
+    });
+
+    assert.strictEqual(visited.size, 1);
+    visited.forEach(object => {
+      assert.strictEqual(schema.getType('Query'), object);
+    });
+  });
 });