fix graphql#1277 ensure interface has at least 1 concrete type

Author: mattkrick

src/type/schema.js

@@ -8,6 +8,7 @@
  */
 
 import {
+  isAbstractType,
   isObjectType,
   isInterfaceType,
   isUnionType,
@@ -159,6 +160,8 @@ export class GraphQLSchema {
             this._implementations[iface.name] = [type];
           }
         });
+      } else if (isAbstractType(type) && !this._implementations[type.name]) {
+        this._implementations[type.name] = [];
       }
     });
   }

src/type/validate.js

@@ -257,6 +257,9 @@ function validateTypes(context: SchemaValidationContext): void {
     } else if (isInterfaceType(type)) {
       // Ensure fields are valid.
       validateFields(context, type);
+
+      // Ensure Interfaces include at least 1 concrete type.
+      validateInterfaces(context, type);
     } else if (isUnionType(type)) {
       // Ensure Unions include valid member types.
       validateUnionMembers(context, type);
@@ -355,6 +358,21 @@ function validateObjectInterfaces(
   });
 }
 
+function validateInterfaces(
+  context: SchemaValidationContext,
+  iface: GraphQLInterfaceType,
+): void {
+  const possibleTypes = context.schema.getPossibleTypes(iface);
+
+  if (possibleTypes.length === 0) {
+    context.reportError(
+      `No concrete types found for Interface type ${iface.name}. ` +
+        `If only referenced via abstraction, add concrete types to schema.types array`,
+      iface.astNode,
+    );
+  }
+}
+
 function validateObjectImplementsInterface(
   context: SchemaValidationContext,
   object: GraphQLObjectType,