More verbose error on missing field

pkg/api/converter.go

@@ -141,11 +141,11 @@ func (c *Converter) convert(sv, dv reflect.Value) error {
 	case reflect.Struct:
 		for i := 0; i < dt.NumField(); i++ {
 			f := dv.Type().Field(i)
-			df := dv.FieldByName(f.Name)
 			sf := sv.FieldByName(f.Name)
-			if !df.IsValid() || !sf.IsValid() {
-				return fmt.Errorf("%v not present in source and dest.", f.Name)
+			if !sf.IsValid() {
+				return fmt.Errorf("%v not present in source %v for dest %v", f.Name, sv.Type(), dv.Type())
 			}
+			df := dv.Field(i)
 			if err := c.convert(sf, df); err != nil {
 				return err
 			}

pkg/api/converter_test.go

@@ -79,3 +79,32 @@ func TestConverter(t *testing.T) {
 		t.Errorf("unexpected non-error")
 	}
 }
+
+func anonymousEmptyTypeNamedA() interface{} {
+	type A struct{}
+	return &A{}
+}
+
+func TestCopyConvertor(t *testing.T) {
+	type A struct {
+		Bar string
+	}
+	type B struct {
+		Bar string
+	}
+	c := NewConverter()
+	err := c.Convert(anonymousEmptyTypeNamedA(), &A{})
+	if err == nil {
+		t.Errorf("unexpected non-error")
+	}
+
+	err = c.Convert(&A{}, anonymousEmptyTypeNamedA())
+	if err != nil {
+		t.Fatalf("unexpected error %v", err)
+	}
+
+	err = c.Convert(&B{}, &A{})
+	if err == nil {
+		t.Errorf("unexpected non-error")
+	}
+}