ResourceNames() should prohibit unnamed arguments

resource.Builder should prohibit empty resource names (the error is from
the wrong place) so that commands that work on multiple resources but
not resource types can properly limit errors.

pkg/kubectl/resource/builder.go

@@ -212,6 +212,10 @@ func (b *Builder) ResourceNames(resource string, names ...string) *Builder {
 			b.resourceTuples = append(b.resourceTuples, tuple)
 			continue
 		}
+		if len(resource) == 0 {
+			b.errs = append(b.errs, fmt.Errorf("the argument %q must be RESOURCE/NAME", name))
+			continue
+		}
 
 		// Use the given default type to create a resource tuple
 		b.resourceTuples = append(b.resourceTuples, resourceTuple{Resource: resource, Name: name})

pkg/kubectl/resource/builder_test.go

@@ -626,6 +626,28 @@ func TestResourceNames(t *testing.T) {
 	}
 }
 
+func TestResourceNamesWithoutResource(t *testing.T) {
+	pods, svc := testData()
+	b := NewBuilder(testapi.Default.RESTMapper(), api.Scheme, fakeClientWith("", t, map[string]string{
+		"/namespaces/test/pods/foo":     runtime.EncodeOrDie(testapi.Default.Codec(), &pods.Items[0]),
+		"/namespaces/test/services/baz": runtime.EncodeOrDie(testapi.Default.Codec(), &svc.Items[0]),
+	}), testapi.Default.Codec()).
+		NamespaceParam("test")
+
+	test := &testVisitor{}
+
+	if b.Do().Err() == nil {
+		t.Errorf("unexpected non-error")
+	}
+
+	b.ResourceNames("", "foo", "services/baz")
+
+	err := b.Do().Visit(test.Handle)
+	if err == nil || !strings.Contains(err.Error(), "must be RESOURCE/NAME") {
+		t.Fatalf("unexpected response: %v", err)
+	}
+}
+
 func TestResourceByNameWithoutRequireObject(t *testing.T) {
 	b := NewBuilder(testapi.Default.RESTMapper(), api.Scheme, fakeClientWith("", t, map[string]string{}), testapi.Default.Codec()).
 		NamespaceParam("test")