Cache client schema exe function, and include test for unreferenced i…

…nterface

src/utilities/__tests__/buildClientSchema.js

@@ -223,6 +223,36 @@ describe('Type System: build schema from introspection', () => {
     await testSchema(schema);
   });
 
+  it('builds a schema with an implicit interface', async () => {
+    const friendlyType = new GraphQLInterfaceType({
+      name: 'Friendly',
+      resolveType: () => null,
+      fields: () => ({
+        bestFriend: {
+          type: friendlyType,
+          description: 'The best friend of this friendly thing'
+        }
+      })
+    });
+    const dogType = new GraphQLObjectType({
+      name: 'Dog',
+      interfaces: [ friendlyType ],
+      fields: () => ({
+        bestFriend: { type: dogType }
+      })
+    });
+    const schema = new GraphQLSchema({
+      query: new GraphQLObjectType({
+        name: 'WithInterface',
+        fields: {
+          dog: { type: dogType }
+        }
+      })
+    });
+
+    await testSchema(schema);
+  });
+
   it('builds a schema with a union', async () => {
     const dogType = new GraphQLObjectType({
       name: 'Dog',

src/utilities/buildClientSchema.js

@@ -235,9 +235,7 @@ export function buildClientSchema(
       name: interfaceIntrospection.name,
       description: interfaceIntrospection.description,
       fields: () => buildFieldDefMap(interfaceIntrospection),
-      resolveType: () => {
-        throw new Error('Client Schema cannot be used for execution.');
-      }
+      resolveType: cannotExecuteClientSchema,
     });
   }
 
@@ -248,9 +246,7 @@ export function buildClientSchema(
       name: unionIntrospection.name,
       description: unionIntrospection.description,
       types: unionIntrospection.possibleTypes.map(getObjectType),
-      resolveType: () => {
-        throw new Error('Client Schema cannot be used for execution.');
-      }
+      resolveType: cannotExecuteClientSchema,
     });
   }
 
@@ -290,9 +286,7 @@ export function buildClientSchema(
         deprecationReason: fieldIntrospection.deprecationReason,
         type: getOutputType(fieldIntrospection.type),
         args: buildInputValueDefMap(fieldIntrospection.args),
-        resolve: () => {
-          throw new Error('Client Schema cannot be used for execution.');
-        },
+        resolve: cannotExecuteClientSchema,
       })
     );
   }
@@ -377,3 +371,7 @@ export function buildClientSchema(
     directives,
   });
 }
+
+function cannotExecuteClientSchema() {
+  throw new Error('Client Schema cannot be used for execution.');
+}